diff --git a/README.md b/README.md
index ddd81af..571a881 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,7 @@ You can find information and documentation [on the official web page](https://ww
 
 ## Legal
 
-Copyright (C) 2021-2023 Orastron Srl unipersonale.
+Copyright (C) 2021-2024 Orastron Srl unipersonale.
 
 Authors: Stefano D'Angelo, Paolo Marrone.
 
diff --git a/THANKS.md b/THANKS.md
index 517f199..9fcb4cb 100644
--- a/THANKS.md
+++ b/THANKS.md
@@ -1,5 +1,8 @@
 We wish to thank and give credit to:
-- the adopters of this software, of which at the moment we can only publicly mention our friends at [Elk Audio](https://www.elk.audio/);
+- the adopters of this software, of which at the moment we can publicly mention, in alphabetical order:
+  - [Elk Audio](https://www.elk.audio/);
+  - [Faselunare](http://faselunare.com/);
+- Kevin Molcard for finding compilation warnings that needed fixing in Brickworks 1.0.0;
 - users participating to [this thread on the KVR Audio forum](https://www.kvraudio.com/forum/viewtopic.php?f=33&t=589519) for providing useful feedback;
 - [Mads Kjeldgaard](https://madskjeldgaard.dk/) for publishing [instructions to build for the Daisy Seed and uploading the firmware](https://madskjeldgaard.dk/posts/daisy-setup/);
 - [Hereket](https://hereket.github.io/) for providing instructions on [how to build an Android app without Android Studio or Gradle](https://hereket.github.io/posts/android_from_command_line/);
diff --git a/include/bw_ap1.h b/include/bw_ap1.h
index 9fdf5e9..002a890 100644
--- a/include/bw_ap1.h
+++ b/include/bw_ap1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order allpass filter (90° shift at cutoff, approaching 180° shift
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_ap1_reset_state_multi()</code> and updated C++
@@ -149,7 +154,7 @@ static inline void bw_ap1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_ap1_update_coeffs_ctrl()
  *  ```>>> */
@@ -263,8 +268,8 @@ static inline char bw_ap1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_ap1_state`.
@@ -317,7 +322,7 @@ struct bw_ap1_state {
 
 static inline void bw_ap1_init(
 		bw_ap1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_lp1_init(&coeffs->lp1_coeffs);
 
@@ -333,7 +338,7 @@ static inline void bw_ap1_init(
 static inline void bw_ap1_set_sample_rate(
 		bw_ap1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -349,7 +354,7 @@ static inline void bw_ap1_set_sample_rate(
 
 static inline void bw_ap1_reset_coeffs(
 		bw_ap1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_set_sample_rate);
 
@@ -367,10 +372,10 @@ static inline float bw_ap1_reset_state(
 		const bw_ap1_coeffs * BW_RESTRICT coeffs,
 		bw_ap1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float lp = bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, x_0);
@@ -394,18 +399,18 @@ static inline void bw_ap1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_ap1_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -414,12 +419,12 @@ static inline void bw_ap1_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_ap1_update_coeffs_ctrl(
 		bw_ap1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
 
@@ -431,7 +436,7 @@ static inline void bw_ap1_update_coeffs_ctrl(
 
 static inline void bw_ap1_update_coeffs_audio(
 		bw_ap1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
 
@@ -445,10 +450,10 @@ static inline float bw_ap1_process1(
 		const bw_ap1_coeffs * BW_RESTRICT coeffs,
 		bw_ap1_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -469,14 +474,14 @@ static inline void bw_ap1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_ap1_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -497,17 +502,17 @@ static inline void bw_ap1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -528,7 +533,7 @@ static inline void bw_ap1_process_multi(
 static inline void bw_ap1_set_cutoff(
 		bw_ap1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -543,7 +548,7 @@ static inline void bw_ap1_set_cutoff(
 static inline void bw_ap1_set_prewarp_at_cutoff(
 		bw_ap1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_init);
 
@@ -556,7 +561,7 @@ static inline void bw_ap1_set_prewarp_at_cutoff(
 static inline void bw_ap1_set_prewarp_freq(
 		bw_ap1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -570,7 +575,7 @@ static inline void bw_ap1_set_prewarp_freq(
 
 static inline char bw_ap1_coeffs_is_valid(
 		const bw_ap1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ap1_coeffs"))
@@ -585,17 +590,17 @@ static inline char bw_ap1_coeffs_is_valid(
 static inline char bw_ap1_state_is_valid(
 		const bw_ap1_coeffs * BW_RESTRICT coeffs,
 		const bw_ap1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_ap1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : NULL, &state->lp1_state);
+	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_ap2.h b/include/bw_ap2.h
index b9ed2db..2b257ad 100644
--- a/include/bw_ap2.h
+++ b/include/bw_ap2.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order allpass filter (180° shift at cutoff, approaching 360° shift
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_ap2_reset_state_multi()</code> and updated C++
@@ -146,7 +151,7 @@ static inline void bw_ap2_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_ap2_update_coeffs_ctrl()
  *  ```>>> */
@@ -272,8 +277,8 @@ static inline char bw_ap2_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_ap2_state`.
@@ -326,7 +331,7 @@ struct bw_ap2_state {
 
 static inline void bw_ap2_init(
 		bw_ap2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->svf_coeffs);
 
@@ -342,7 +347,7 @@ static inline void bw_ap2_init(
 static inline void bw_ap2_set_sample_rate(
 		bw_ap2_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -358,7 +363,7 @@ static inline void bw_ap2_set_sample_rate(
 
 static inline void bw_ap2_reset_coeffs(
 		bw_ap2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_set_sample_rate);
 
@@ -376,10 +381,10 @@ static inline float bw_ap2_reset_state(
 		const bw_ap2_coeffs * BW_RESTRICT coeffs,
 		bw_ap2_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float lp, bp, hp;
@@ -405,18 +410,18 @@ static inline void bw_ap2_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_ap2_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -425,12 +430,12 @@ static inline void bw_ap2_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_ap2_update_coeffs_ctrl(
 		bw_ap2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
 
@@ -442,7 +447,7 @@ static inline void bw_ap2_update_coeffs_ctrl(
 
 static inline void bw_ap2_update_coeffs_audio(
 		bw_ap2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
 
@@ -456,10 +461,10 @@ static inline float bw_ap2_process1(
 		const bw_ap2_coeffs * BW_RESTRICT coeffs,
 		bw_ap2_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -482,14 +487,14 @@ static inline void bw_ap2_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_ap2_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -510,17 +515,17 @@ static inline void bw_ap2_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -541,7 +546,7 @@ static inline void bw_ap2_process_multi(
 static inline void bw_ap2_set_cutoff(
 		bw_ap2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -556,7 +561,7 @@ static inline void bw_ap2_set_cutoff(
 static inline void bw_ap2_set_Q(
 		bw_ap2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -571,7 +576,7 @@ static inline void bw_ap2_set_Q(
 static inline void bw_ap2_set_prewarp_at_cutoff(
 		bw_ap2_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_init);
 
@@ -584,7 +589,7 @@ static inline void bw_ap2_set_prewarp_at_cutoff(
 static inline void bw_ap2_set_prewarp_freq(
 		bw_ap2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ap2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ap2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -598,7 +603,7 @@ static inline void bw_ap2_set_prewarp_freq(
 
 static inline char bw_ap2_coeffs_is_valid(
 		const bw_ap2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ap2_coeffs"))
@@ -613,17 +618,17 @@ static inline char bw_ap2_coeffs_is_valid(
 static inline char bw_ap2_state_is_valid(
 		const bw_ap2_coeffs * BW_RESTRICT coeffs,
 		const bw_ap2_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_ap2_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : NULL, &state->svf_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : BW_NULL, &state->svf_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_balance.h b/include/bw_balance.h
index b742157..8f8d801 100644
--- a/include/bw_balance.h
+++ b/include/bw_balance.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole }}}
  *  description {{{
  *    Stereo balance.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li><code>bw_balance_process()</code> and
@@ -229,7 +234,7 @@ struct bw_balance_coeffs {
 
 static inline void bw_balance_init(
 		bw_balance_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_gain_init(&coeffs->l_coeffs);
 	bw_gain_init(&coeffs->r_coeffs);
@@ -246,7 +251,7 @@ static inline void bw_balance_init(
 static inline void bw_balance_set_sample_rate(
 		bw_balance_coeffs * BW_RESTRICT coeffs,
 		float                           sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -273,7 +278,7 @@ static inline void bw_balance_do_update_coeffs(
 
 static inline void bw_balance_reset_coeffs(
 		bw_balance_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_set_sample_rate);
 
@@ -290,7 +295,7 @@ static inline void bw_balance_reset_coeffs(
 
 static inline void bw_balance_update_coeffs_ctrl(
 		bw_balance_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_reset_coeffs);
 
@@ -304,7 +309,7 @@ static inline void bw_balance_update_coeffs_ctrl(
 
 static inline void bw_balance_update_coeffs_audio(
 		bw_balance_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_reset_coeffs);
 
@@ -321,7 +326,7 @@ static inline void bw_balance_process1(
 		float                                 x_r,
 		float * BW_RESTRICT                   y_l,
 		float * BW_RESTRICT                   y_r) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x_l));
@@ -344,15 +349,15 @@ static inline void bw_balance_process(
 		float *                         y_l,
 		float *                         y_r,
 		size_t                          n_samples){
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_l != NULL);
+	BW_ASSERT(x_l != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_l, n_samples));
-	BW_ASSERT(x_r != NULL);
+	BW_ASSERT(x_r != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_r, n_samples));
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 
 	bw_balance_update_coeffs_ctrl(coeffs);
@@ -375,13 +380,13 @@ static inline void bw_balance_process_multi(
 		float * const *                 y_r,
 		size_t                          n_channels,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_l != NULL);
-	BW_ASSERT(x_r != NULL);
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(x_l != BW_NULL);
+	BW_ASSERT(x_r != BW_NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
@@ -408,7 +413,7 @@ static inline void bw_balance_process_multi(
 static inline void bw_balance_set_balance(
 		bw_balance_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_balance_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_balance_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -422,7 +427,7 @@ static inline void bw_balance_set_balance(
 
 static inline char bw_balance_coeffs_is_valid(
 		const bw_balance_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_balance_coeffs"))
diff --git a/include/bw_bd_reduce.h b/include/bw_bd_reduce.h
index 5d46607..95b0fef 100644
--- a/include/bw_bd_reduce.h
+++ b/include/bw_bd_reduce.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Bit depth reducer.
@@ -31,6 +31,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_bd_reduce_set_sample_rate()</code>.</li>
@@ -225,7 +230,7 @@ struct bw_bd_reduce_coeffs {
 
 static inline void bw_bd_reduce_init(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->bit_depth = 16;
 
@@ -240,7 +245,7 @@ static inline void bw_bd_reduce_init(
 static inline void bw_bd_reduce_set_sample_rate(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -267,7 +272,7 @@ static inline void bw_bd_reduce_do_update_coeffs_ctrl(
 
 static inline void bw_bd_reduce_reset_coeffs(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_set_sample_rate);
 
@@ -283,7 +288,7 @@ static inline void bw_bd_reduce_reset_coeffs(
 
 static inline void bw_bd_reduce_update_coeffs_ctrl(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
 
@@ -295,7 +300,7 @@ static inline void bw_bd_reduce_update_coeffs_ctrl(
 
 static inline void bw_bd_reduce_update_coeffs_audio(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
 
@@ -305,7 +310,7 @@ static inline void bw_bd_reduce_update_coeffs_audio(
 static inline float bw_bd_reduce_process1(
 		const bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
 		float                                   x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -324,12 +329,12 @@ static inline void bw_bd_reduce_process(
 		const float *                     x,
 		float *                           y,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_bd_reduce_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++)
@@ -346,11 +351,11 @@ static inline void bw_bd_reduce_process_multi(
 		float * const *                   y,
 		size_t                            n_channels,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -369,7 +374,7 @@ static inline void bw_bd_reduce_process_multi(
 static inline void bw_bd_reduce_set_bit_depth(
 		bw_bd_reduce_coeffs * BW_RESTRICT coeffs,
 		char                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_bd_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_bd_reduce_coeffs_state_init);
 	BW_ASSERT(value >= 1 && value <= 64);
@@ -382,7 +387,7 @@ static inline void bw_bd_reduce_set_bit_depth(
 
 static inline char bw_bd_reduce_coeffs_is_valid(
 		const bw_bd_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_bd_reduce_coeffs"))
diff --git a/include/bw_buf.h b/include/bw_buf.h
index 6c298e6..c8d5c10 100644
--- a/include/bw_buf.h
+++ b/include/bw_buf.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Common operations on buffers.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Now using <code>size_t</code> instead of
@@ -240,7 +245,7 @@ static inline void bw_buf_fill(
 		float * BW_RESTRICT dest,
 		size_t              n_elems) {
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = k;
@@ -252,9 +257,9 @@ static inline void bw_buf_neg(
 		const float * src,
 		float *       dest,
 		size_t        n_elems) {
-	BW_ASSERT(src != NULL);
+	BW_ASSERT(src != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src, n_elems));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = -src[i];
@@ -267,10 +272,10 @@ static inline void bw_buf_add(
 		float         k,
 		float *       dest,
 		size_t        n_elems) {
-	BW_ASSERT(src != NULL);
+	BW_ASSERT(src != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src, n_elems));
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = k + src[i];
@@ -283,10 +288,10 @@ static inline void bw_buf_scale(
 		float         k,
 		float *       dest,
 		size_t        n_elems) {
-	BW_ASSERT(src != NULL);
+	BW_ASSERT(src != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src, n_elems));
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = k * src[i];
@@ -299,11 +304,11 @@ static inline void bw_buf_mix(
 		const float * src2,
 		float *       dest,
 		size_t        n_elems) {
-	BW_ASSERT(src1 != NULL);
+	BW_ASSERT(src1 != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src1, n_elems));
-	BW_ASSERT(src2 != NULL);
+	BW_ASSERT(src2 != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src2, n_elems));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = src1[i] + src2[i];
@@ -316,11 +321,11 @@ static inline void bw_buf_mul(
 		const float * src2,
 		float *       dest,
 		size_t        n_elems) {
-	BW_ASSERT(src1 != NULL);
+	BW_ASSERT(src1 != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src1, n_elems));
-	BW_ASSERT(src2 != NULL);
+	BW_ASSERT(src2 != BW_NULL);
 	BW_ASSERT_DEEP(!bw_has_nan(src2, n_elems));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 
 	for (size_t i = 0; i < n_elems; i++)
 		dest[i] = src1[i] * src2[i];
@@ -334,7 +339,7 @@ static inline void bw_buf_fill_multi(
 		size_t                                  n_channels,
 		size_t                                  n_elems) {
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -350,8 +355,8 @@ static inline void bw_buf_neg_multi(
 		float * const *       dest,
 		size_t                n_channels,
 		size_t                n_elems) {
-	BW_ASSERT(src != NULL);
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(src != BW_NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -368,9 +373,9 @@ static inline void bw_buf_add_multi(
 		float * const *       dest,
 		size_t                n_channels,
 		size_t                n_elems) {
-	BW_ASSERT(src != NULL);
+	BW_ASSERT(src != BW_NULL);
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -387,9 +392,9 @@ static inline void bw_buf_scale_multi(
 		float * const *       dest,
 		size_t                n_channels,
 		size_t                n_elems) {
-	BW_ASSERT(src != NULL);
+	BW_ASSERT(src != BW_NULL);
 	BW_ASSERT(!bw_is_nan(k));
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -406,9 +411,9 @@ static inline void bw_buf_mix_multi(
 		float * const *       dest,
 		size_t                n_channels,
 		size_t                n_elems) {
-	BW_ASSERT(src1 != NULL);
-	BW_ASSERT(src2 != NULL);
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(src1 != BW_NULL);
+	BW_ASSERT(src2 != BW_NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -425,9 +430,9 @@ static inline void bw_buf_mul_multi(
 		float * const *       dest,
 		size_t                n_channels,
 		size_t                n_elems) {
-	BW_ASSERT(src1 != NULL);
-	BW_ASSERT(src2 != NULL);
-	BW_ASSERT(dest != NULL);
+	BW_ASSERT(src1 != BW_NULL);
+	BW_ASSERT(src2 != BW_NULL);
+	BW_ASSERT(dest != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
diff --git a/include/bw_cab.h b/include/bw_cab.h
index fe6032c..ac39f42 100644
--- a/include/bw_cab.h
+++ b/include/bw_cab.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -109,7 +109,7 @@ static inline void bw_cab_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_cab_update_coeffs_ctrl()
  *  ```>>> */
@@ -222,7 +222,7 @@ static inline char bw_cab_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed (`state`
  *    is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
@@ -285,7 +285,7 @@ struct bw_cab_state {
 
 static inline void bw_cab_init(
 		bw_cab_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->lp_coeffs);
 	bw_svf_init(&coeffs->hp_coeffs);
@@ -313,7 +313,7 @@ static inline void bw_cab_init(
 static inline void bw_cab_set_sample_rate(
 		bw_cab_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -334,7 +334,7 @@ static inline void bw_cab_set_sample_rate(
 
 static inline void bw_cab_reset_coeffs(
 		bw_cab_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_set_sample_rate);
 
@@ -357,10 +357,10 @@ static inline float bw_cab_reset_state(
 		const bw_cab_coeffs * BW_RESTRICT coeffs,
 		bw_cab_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float v_lp, v_hp, v_bp;
@@ -392,18 +392,18 @@ static inline void bw_cab_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_cab_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -412,12 +412,12 @@ static inline void bw_cab_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_cab_update_coeffs_ctrl(
 		bw_cab_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
 
@@ -434,7 +434,7 @@ static inline void bw_cab_update_coeffs_ctrl(
 
 static inline void bw_cab_update_coeffs_audio(
 		bw_cab_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
 
@@ -453,10 +453,10 @@ static inline float bw_cab_process1(
 		const bw_cab_coeffs * BW_RESTRICT coeffs,
 		bw_cab_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -485,14 +485,14 @@ static inline void bw_cab_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_cab_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -513,17 +513,17 @@ static inline void bw_cab_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -544,7 +544,7 @@ static inline void bw_cab_process_multi(
 static inline void bw_cab_set_cutoff_low(
 		bw_cab_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -561,7 +561,7 @@ static inline void bw_cab_set_cutoff_low(
 static inline void bw_cab_set_cutoff_high(
 		bw_cab_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -578,7 +578,7 @@ static inline void bw_cab_set_cutoff_high(
 static inline void bw_cab_set_tone(
 		bw_cab_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_cab_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_cab_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -593,7 +593,7 @@ static inline void bw_cab_set_tone(
 
 static inline char bw_cab_coeffs_is_valid(
 		const bw_cab_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_cab_coeffs"))
@@ -613,20 +613,20 @@ static inline char bw_cab_coeffs_is_valid(
 static inline char bw_cab_state_is_valid(
 		const bw_cab_coeffs * BW_RESTRICT coeffs,
 		const bw_cab_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_cab_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->lp_coeffs : NULL, &state->lp_state)
-		&& bw_svf_state_is_valid(coeffs ? &coeffs->hp_coeffs : NULL, &state->hp_state)
-		&& bw_svf_state_is_valid(coeffs ? &coeffs->bpl_coeffs : NULL, &state->bpl_state)
-		&& bw_svf_state_is_valid(coeffs ? &coeffs->bph_coeffs : NULL, &state->bph_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->lp_coeffs : BW_NULL, &state->lp_state)
+		&& bw_svf_state_is_valid(coeffs ? &coeffs->hp_coeffs : BW_NULL, &state->hp_state)
+		&& bw_svf_state_is_valid(coeffs ? &coeffs->bpl_coeffs : BW_NULL, &state->bpl_state)
+		&& bw_svf_state_is_valid(coeffs ? &coeffs->bph_coeffs : BW_NULL, &state->bph_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_chorus.h b/include/bw_chorus.h
index b265c5e..dc229ec 100644
--- a/include/bw_chorus.h
+++ b/include/bw_chorus.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_buf bw_comb bw_common bw_delay bw_gain bw_math bw_one_pole bw_osc_sin
  *    bw_phase_gen
@@ -36,6 +36,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial value argument in
@@ -178,7 +183,7 @@ static inline void bw_chorus_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    If parameter `coeff_fb`  has value `-1.f` or `1.f`, then `x_0` must only
  *    contain `0.f`.
@@ -335,8 +340,8 @@ static inline char bw_chorus_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_chorus_state`.
@@ -407,7 +412,7 @@ struct bw_chorus_state {
 static inline void bw_chorus_init(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          max_delay) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT(bw_is_finite(max_delay));
 	BW_ASSERT(max_delay >= 0.f);
 
@@ -428,7 +433,7 @@ static inline void bw_chorus_init(
 static inline void bw_chorus_set_sample_rate(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -445,7 +450,7 @@ static inline void bw_chorus_set_sample_rate(
 
 static inline size_t bw_chorus_mem_req(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_set_sample_rate);
 
@@ -456,11 +461,11 @@ static inline void bw_chorus_mem_set(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs,
 		bw_chorus_state * BW_RESTRICT        state,
 		void * BW_RESTRICT                   mem) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_set_sample_rate);
-	BW_ASSERT(state != NULL);
-	BW_ASSERT(mem != NULL);
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT(mem != BW_NULL);
 
 	bw_comb_mem_set(&coeffs->comb_coeffs, &state->comb_state, mem);
 
@@ -476,7 +481,7 @@ static inline void bw_chorus_mem_set(
 
 static inline void bw_chorus_reset_coeffs(
 		bw_chorus_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_set_sample_rate);
 
@@ -499,10 +504,10 @@ static inline float bw_chorus_reset_state(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs,
 		bw_chorus_state * BW_RESTRICT        state,
 		float                                x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_chorus_state_state_mem_set);
 	BW_ASSERT(bw_is_finite(x_0));
@@ -528,18 +533,18 @@ static inline void bw_chorus_reset_state_multi(
 		const float *                                     x_0,
 		float *                                           y_0,
 		size_t                                            n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_chorus_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -548,12 +553,12 @@ static inline void bw_chorus_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_chorus_update_coeffs_ctrl(
 		bw_chorus_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
 
@@ -566,7 +571,7 @@ static inline void bw_chorus_update_coeffs_ctrl(
 
 static inline void bw_chorus_update_coeffs_audio(
 		bw_chorus_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
 
@@ -586,10 +591,10 @@ static inline float bw_chorus_process1(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs,
 		bw_chorus_state * BW_RESTRICT        state,
 		float                                x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_chorus_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
@@ -611,15 +616,15 @@ static inline void bw_chorus_process(
 		const float *                  x,
 		float *                        y,
 		size_t                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_chorus_state_state_reset_state);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_chorus_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -641,17 +646,17 @@ static inline void bw_chorus_process_multi(
 		float * const *                                   y,
 		size_t                                            n_channels,
 		size_t                                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -672,7 +677,7 @@ static inline void bw_chorus_process_multi(
 static inline void bw_chorus_set_rate(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -686,7 +691,7 @@ static inline void bw_chorus_set_rate(
 static inline void bw_chorus_set_delay(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -701,7 +706,7 @@ static inline void bw_chorus_set_delay(
 static inline void bw_chorus_set_amount(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -712,7 +717,7 @@ static inline void bw_chorus_set_amount(
 static inline void bw_chorus_set_coeff_x(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -726,7 +731,7 @@ static inline void bw_chorus_set_coeff_x(
 static inline void bw_chorus_set_coeff_mod(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -740,7 +745,7 @@ static inline void bw_chorus_set_coeff_mod(
 static inline void bw_chorus_set_coeff_fb(
 		bw_chorus_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_chorus_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_chorus_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -754,7 +759,7 @@ static inline void bw_chorus_set_coeff_fb(
 
 static inline char bw_chorus_coeffs_is_valid(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_chorus_coeffs"))
@@ -782,7 +787,7 @@ static inline char bw_chorus_coeffs_is_valid(
 static inline char bw_chorus_state_is_valid(
 		const bw_chorus_coeffs * BW_RESTRICT coeffs,
 		const bw_chorus_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_chorus_state"))
@@ -790,11 +795,11 @@ static inline char bw_chorus_state_is_valid(
 	if (state->state < bw_chorus_state_state_mem_set || state->state > bw_chorus_state_state_reset_state)
 		return 0;
 
-	if (state->state >= bw_chorus_state_state_reset_state && coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (state->state >= bw_chorus_state_state_reset_state && coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_comb_state_is_valid(coeffs ? &coeffs->comb_coeffs : NULL, &state->comb_state);
+	return bw_comb_state_is_valid(coeffs ? &coeffs->comb_coeffs : BW_NULL, &state->comb_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_clip.h b/include/bw_clip.h
index 1a3e22f..11b6958 100644
--- a/include/bw_clip.h
+++ b/include/bw_clip.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Antialiased hard clipper with parametric bias and gain
@@ -45,6 +45,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Changed default value for gain compensation to off.</li>
@@ -153,7 +158,7 @@ static inline void bw_clip_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_clip_update_coeffs_ctrl()
  *  ```>>> */
@@ -275,8 +280,8 @@ static inline char bw_clip_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_clip_state`.
@@ -342,7 +347,7 @@ struct bw_clip_state {
 
 static inline void bw_clip_init(
 		bw_clip_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -363,7 +368,7 @@ static inline void bw_clip_init(
 static inline void bw_clip_set_sample_rate(
 		bw_clip_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -395,7 +400,7 @@ static inline void bw_clip_do_update_coeffs(
 
 static inline void bw_clip_reset_coeffs(
 		bw_clip_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_set_sample_rate);
 
@@ -415,10 +420,10 @@ static inline float bw_clip_reset_state(
 		const bw_clip_coeffs * BW_RESTRICT coeffs,
 		bw_clip_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float x = bw_one_pole_get_y_z1(&coeffs->smooth_gain_state) * x_0 + bw_one_pole_get_y_z1(&coeffs->smooth_bias_state);
@@ -447,18 +452,18 @@ static inline void bw_clip_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_clip_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -467,12 +472,12 @@ static inline void bw_clip_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_clip_update_coeffs_ctrl(
 		bw_clip_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
 
@@ -481,7 +486,7 @@ static inline void bw_clip_update_coeffs_ctrl(
 
 static inline void bw_clip_update_coeffs_audio(
 		bw_clip_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
 
@@ -495,10 +500,10 @@ static inline float bw_clip_process1(
 		const bw_clip_coeffs * BW_RESTRICT coeffs,
 		bw_clip_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -523,10 +528,10 @@ static inline float bw_clip_process1_comp(
 		const bw_clip_coeffs * BW_RESTRICT coeffs,
 		bw_clip_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -546,14 +551,14 @@ static inline void bw_clip_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->gain_compensation)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -579,17 +584,17 @@ static inline void bw_clip_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -616,7 +621,7 @@ static inline void bw_clip_process_multi(
 static inline void bw_clip_set_bias(
 		bw_clip_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -631,7 +636,7 @@ static inline void bw_clip_set_bias(
 static inline void bw_clip_set_gain(
 		bw_clip_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -646,7 +651,7 @@ static inline void bw_clip_set_gain(
 static inline void bw_clip_set_gain_compensation(
 		bw_clip_coeffs * BW_RESTRICT coeffs,
 		char                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_clip_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_clip_coeffs_state_init);
 
@@ -658,7 +663,7 @@ static inline void bw_clip_set_gain_compensation(
 
 static inline char bw_clip_coeffs_is_valid(
 		const bw_clip_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_clip_coeffs"))
@@ -695,13 +700,13 @@ static inline char bw_clip_coeffs_is_valid(
 static inline char bw_clip_state_is_valid(
 		const bw_clip_coeffs * BW_RESTRICT coeffs,
 		const bw_clip_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_clip_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_comb.h b/include/bw_comb.h
index ac1cde2..6602b1f 100644
--- a/include/bw_comb.h
+++ b/include/bw_comb.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_buf bw_common bw_delay bw_gain bw_math bw_one_pole
  *  }}}
@@ -37,6 +37,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial value argument in
@@ -179,7 +184,7 @@ static inline void bw_comb_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    If parameter `coeff_fb`  has value `-1.f` or `1.f`, then `x_0` must only
  *    contain `0.f`.
@@ -322,8 +327,8 @@ static inline char bw_comb_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_comb_state`.
@@ -407,7 +412,7 @@ struct bw_comb_state {
 static inline void bw_comb_init(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        max_delay) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT(bw_is_finite(max_delay));
 	BW_ASSERT(max_delay >= 0.f);
 
@@ -435,7 +440,7 @@ static inline void bw_comb_init(
 static inline void bw_comb_set_sample_rate(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -457,7 +462,7 @@ static inline void bw_comb_set_sample_rate(
 
 static inline size_t bw_comb_mem_req(
 		const bw_comb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
 
@@ -468,11 +473,11 @@ static inline void bw_comb_mem_set(
 		const bw_comb_coeffs * BW_RESTRICT coeffs,
 		bw_comb_state * BW_RESTRICT        state,
 		void * BW_RESTRICT                 mem) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
-	BW_ASSERT(state != NULL);
-	BW_ASSERT(mem != NULL);
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT(mem != BW_NULL);
 
 	bw_delay_mem_set(&coeffs->delay_coeffs, &state->delay_state, mem);
 
@@ -519,7 +524,7 @@ static inline void bw_comb_do_update_coeffs(
 
 static inline void bw_comb_reset_coeffs(
 		bw_comb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
 
@@ -543,10 +548,10 @@ static inline float bw_comb_reset_state(
 		const bw_comb_coeffs * BW_RESTRICT coeffs,
 		bw_comb_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_mem_set);
 	BW_ASSERT(bw_is_finite(x_0));
@@ -582,18 +587,18 @@ static inline void bw_comb_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_comb_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -602,12 +607,12 @@ static inline void bw_comb_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_comb_update_coeffs_ctrl(
 		bw_comb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
 
@@ -621,7 +626,7 @@ static inline void bw_comb_update_coeffs_ctrl(
 
 static inline void bw_comb_update_coeffs_audio(
 		bw_comb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
 
@@ -638,10 +643,10 @@ static inline float bw_comb_process1(
 		const bw_comb_coeffs * BW_RESTRICT coeffs,
 		bw_comb_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
@@ -667,15 +672,15 @@ static inline void bw_comb_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_comb_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -697,17 +702,17 @@ static inline void bw_comb_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -728,7 +733,7 @@ static inline void bw_comb_process_multi(
 static inline void bw_comb_set_delay_ff(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -742,7 +747,7 @@ static inline void bw_comb_set_delay_ff(
 static inline void bw_comb_set_delay_fb(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -756,7 +761,7 @@ static inline void bw_comb_set_delay_fb(
 static inline void bw_comb_set_coeff_blend(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -770,7 +775,7 @@ static inline void bw_comb_set_coeff_blend(
 static inline void bw_comb_set_coeff_ff(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -784,7 +789,7 @@ static inline void bw_comb_set_coeff_ff(
 static inline void bw_comb_set_coeff_fb(
 		bw_comb_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -798,7 +803,7 @@ static inline void bw_comb_set_coeff_fb(
 
 static inline char bw_comb_coeffs_is_valid(
 		const bw_comb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_comb_coeffs"))
@@ -849,7 +854,7 @@ static inline char bw_comb_coeffs_is_valid(
 static inline char bw_comb_state_is_valid(
 		const bw_comb_coeffs * BW_RESTRICT coeffs,
 		const bw_comb_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_comb_state"))
@@ -857,11 +862,11 @@ static inline char bw_comb_state_is_valid(
 	if (state->state < bw_comb_state_state_mem_set || state->state > bw_comb_state_state_reset_state)
 		return 0;
 
-	if (state->state >= bw_comb_state_state_reset_state && coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (state->state >= bw_comb_state_state_reset_state && coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_delay_state_is_valid(coeffs ? &coeffs->delay_coeffs : NULL, &state->delay_state);
+	return bw_delay_state_is_valid(coeffs ? &coeffs->delay_coeffs : BW_NULL, &state->delay_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_common.h b/include/bw_common.h
index 96dae6b..5c9efb7 100644
--- a/include/bw_common.h
+++ b/include/bw_common.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,19 @@
 
 /*!
  *  module_type {{{ foundation }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.1.0 }}}
  *  description {{{
  *    A common header to make sure that a bunch of basic definitions are
  *    available and consistent for all Brickworks modules.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.0</strong>:
+ *        <ul>
+ *          <li>Added <code>BW_NULL</code> and relaxed <code>NULL</code> definition
+ *              requirement in C++.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Removed <code>BW_SIZE_T</code> and went for <code>size_t</code>
@@ -91,7 +97,7 @@
  *
  *    Brickworks requires definitions of:
  *
- *    * `NULL` and `size_t`, normally supplied by `stddef.h`;
+ *    * `NULL` (C only) and `size_t`, normally supplied by `stddef.h`;
  *    * `(u)int{8,16,32,64}_t`, `INT{8,16,32,64}_{MIN,MAX}`, and
  *      `UINT{8,16,32,64}_MAX`, normally supplied by `stdint.h`;
  *    * `INFINITY`, normally supplied by `math.h`.
@@ -106,13 +112,20 @@
  *    * if `BW_NO_STDLIB` or `BW_NO_MATH_H` is defined, then `math.h` is not
  *      `#include`d.
  *
+ *    A `BW_NULL` macro is defined whose value is either `NULL` (C) or `nullptr`
+ *    (C++).
  *  >>> */
 #if !defined(BW_NO_STDLIB) && !defined(BW_NO_STDDEF_H)
 # include <stddef.h>
 #endif
 
-#ifndef NULL
-# error NULL not defined
+#ifdef __cplusplus
+# define BW_NULL nullptr
+#else
+# ifndef NULL
+#  error NULL not defined
+# endif
+# define BW_NULL NULL
 #endif
 
 #if !defined(BW_NO_STDLIB) && !defined(BW_NO_STDINT_H)
diff --git a/include/bw_comp.h b/include/bw_comp.h
index f5b976c..2b36eea 100644
--- a/include/bw_comp.h
+++ b/include/bw_comp.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_common bw_env_follow bw_gain bw_math bw_one_pole
  *  }}}
@@ -29,6 +29,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input values to
@@ -150,7 +155,7 @@ static inline void bw_comp_reset_state_multi(
  *    array and sidechain input value in the `x_sc_0` array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_comp_update_coeffs_ctrl()
  *  ```>>> */
@@ -319,8 +324,8 @@ static inline char bw_comp_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_comp_state`.
@@ -388,7 +393,7 @@ struct bw_comp_state {
 
 static inline void bw_comp_init(
 		bw_comp_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_env_follow_init(&coeffs->env_follow_coeffs);
 	bw_gain_init(&coeffs->gain_coeffs);
@@ -409,7 +414,7 @@ static inline void bw_comp_init(
 static inline void bw_comp_set_sample_rate(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -437,7 +442,7 @@ static inline void bw_comp_do_update_coeffs_audio(
 
 static inline void bw_comp_reset_coeffs(
 		bw_comp_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_set_sample_rate);
 
@@ -460,10 +465,10 @@ static inline float bw_comp_reset_state(
 		bw_comp_state * BW_RESTRICT        state,
 		float                              x_0,
 		float                              x_sc_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 	BW_ASSERT(bw_is_finite(x_sc_0));
 
@@ -490,19 +495,19 @@ static inline void bw_comp_reset_state_multi(
 		const float *                                   x_sc_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
-	BW_ASSERT(x_sc_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
+	BW_ASSERT(x_sc_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_comp_reset_state(coeffs, state[i], x_0[i], x_sc_0[i]);
 	else
@@ -512,12 +517,12 @@ static inline void bw_comp_reset_state_multi(
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_has_only_finite(y_0, n_channels));
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_comp_update_coeffs_ctrl(
 		bw_comp_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
 
@@ -530,7 +535,7 @@ static inline void bw_comp_update_coeffs_ctrl(
 
 static inline void bw_comp_update_coeffs_audio(
 		bw_comp_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
 
@@ -549,10 +554,10 @@ static inline float bw_comp_process1(
 		bw_comp_state * BW_RESTRICT        state,
 		float                              x,
 		float                              x_sc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 	BW_ASSERT(bw_is_finite(x_sc));
@@ -576,16 +581,16 @@ static inline void bw_comp_process(
 		const float *                x_sc,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(x_sc != NULL);
+	BW_ASSERT(x_sc != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_sc, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_comp_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -607,18 +612,18 @@ static inline void bw_comp_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(x_sc != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(x_sc != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -639,7 +644,7 @@ static inline void bw_comp_process_multi(
 static inline void bw_comp_set_thresh_lin(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -654,7 +659,7 @@ static inline void bw_comp_set_thresh_lin(
 static inline void bw_comp_set_thresh_dBFS(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -669,7 +674,7 @@ static inline void bw_comp_set_thresh_dBFS(
 static inline void bw_comp_set_ratio(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -684,7 +689,7 @@ static inline void bw_comp_set_ratio(
 static inline void bw_comp_set_attack_tau(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -699,7 +704,7 @@ static inline void bw_comp_set_attack_tau(
 static inline void bw_comp_set_release_tau(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -714,7 +719,7 @@ static inline void bw_comp_set_release_tau(
 static inline void bw_comp_set_gain_lin(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -728,7 +733,7 @@ static inline void bw_comp_set_gain_lin(
 static inline void bw_comp_set_gain_dB(
 		bw_comp_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -742,7 +747,7 @@ static inline void bw_comp_set_gain_dB(
 
 static inline char bw_comp_coeffs_is_valid(
 		const bw_comp_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_comp_coeffs"))
@@ -780,17 +785,17 @@ static inline char bw_comp_coeffs_is_valid(
 static inline char bw_comp_state_is_valid(
 		const bw_comp_coeffs * BW_RESTRICT coeffs,
 		const bw_comp_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_comp_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : NULL, &state->env_follow_state);
+	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : BW_NULL, &state->env_follow_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_delay.h b/include/bw_delay.h
index 1e007d1..1e6a20c 100644
--- a/include/bw_delay.h
+++ b/include/bw_delay.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_buf bw_common bw_math }}}
  *  description {{{
  *    Interpolated delay line, not smoothed.
@@ -31,6 +31,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Removed <code>read()</code> and <code>write()</code> from C++
@@ -171,7 +176,7 @@ static inline void bw_delay_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_delay_read()
  *  ```>>> */
@@ -292,8 +297,8 @@ static inline char bw_delay_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_delay_state`.
@@ -367,7 +372,7 @@ struct bw_delay_state {
 static inline void bw_delay_init(
 		bw_delay_coeffs * BW_RESTRICT coeffs,
 		float                         max_delay) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT(bw_is_finite(max_delay));
 	BW_ASSERT(max_delay >= 0.f);
 
@@ -386,7 +391,7 @@ static inline void bw_delay_init(
 static inline void bw_delay_set_sample_rate(
 		bw_delay_coeffs * BW_RESTRICT coeffs,
 		float                         sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -403,7 +408,7 @@ static inline void bw_delay_set_sample_rate(
 
 static inline size_t bw_delay_mem_req(
 		const bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_set_sample_rate);
 
@@ -414,11 +419,11 @@ static inline void bw_delay_mem_set(
 		const bw_delay_coeffs * BW_RESTRICT coeffs,
 		bw_delay_state * BW_RESTRICT        state,
 		void * BW_RESTRICT                  mem) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_set_sample_rate);
-	BW_ASSERT(state != NULL);
-	BW_ASSERT(mem != NULL);
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT(mem != BW_NULL);
 
 	(void)coeffs;
 	state->buf = (float *)mem;
@@ -444,7 +449,7 @@ static inline void bw_delay_do_update_coeffs_ctrl(bw_delay_coeffs *BW_RESTRICT c
 
 static inline void bw_delay_reset_coeffs(
 		bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_set_sample_rate);
 
@@ -463,10 +468,10 @@ static inline float bw_delay_reset_state(
 		const bw_delay_coeffs * BW_RESTRICT coeffs,
 		bw_delay_state * BW_RESTRICT        state,
 		float                               x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_mem_set);
 	BW_ASSERT(bw_is_finite(x_0));
@@ -494,18 +499,18 @@ static inline void bw_delay_reset_state_multi(
 		const float *                                    x_0,
 		float *                                          y_0,
 		size_t                                           n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_delay_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -514,7 +519,7 @@ static inline void bw_delay_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static float bw_delay_read(
@@ -522,10 +527,10 @@ static float bw_delay_read(
 		const bw_delay_state * BW_RESTRICT  state,
 		size_t                              di,
 		float                               df) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(df));
@@ -549,10 +554,10 @@ static void bw_delay_write(
 		const bw_delay_coeffs * BW_RESTRICT coeffs,
 		bw_delay_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
@@ -569,7 +574,7 @@ static void bw_delay_write(
 
 static inline void bw_delay_update_coeffs_ctrl(
 		bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 
@@ -581,7 +586,7 @@ static inline void bw_delay_update_coeffs_ctrl(
 
 static inline void bw_delay_update_coeffs_audio(
 		bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 
@@ -592,10 +597,10 @@ static inline float bw_delay_process1(
 		const bw_delay_coeffs * BW_RESTRICT coeffs,
 		bw_delay_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
@@ -618,15 +623,15 @@ static inline void bw_delay_process(
 		const float *                 x,
 		float *                       y,
 		size_t                        n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_delay_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++)
@@ -646,17 +651,17 @@ static inline void bw_delay_process_multi(
 		float * const *                                  y,
 		size_t                                           n_channels,
 		size_t                                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -675,7 +680,7 @@ static inline void bw_delay_process_multi(
 static inline void bw_delay_set_delay(
 		bw_delay_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -691,7 +696,7 @@ static inline void bw_delay_set_delay(
 
 static inline size_t bw_delay_get_length(
 		const bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_set_sample_rate);
 
@@ -700,7 +705,7 @@ static inline size_t bw_delay_get_length(
 
 static inline char bw_delay_coeffs_is_valid(
 		const bw_delay_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_delay_coeffs"))
@@ -736,7 +741,7 @@ static inline char bw_delay_coeffs_is_valid(
 static inline char bw_delay_state_is_valid(
 		const bw_delay_coeffs * BW_RESTRICT coeffs,
 		const bw_delay_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_delay_state"))
@@ -747,11 +752,11 @@ static inline char bw_delay_state_is_valid(
 
 	(void)coeffs;
 
-	if (state->buf == NULL)
+	if (state->buf == BW_NULL)
 		return 0;
 
 #ifdef BW_DEBUG_DEEP
-	if (state->state >= bw_delay_state_state_reset_state && coeffs != NULL) {
+	if (state->state >= bw_delay_state_state_reset_state && coeffs != BW_NULL) {
 		if (coeffs->reset_id != state->coeffs_reset_id)
 			return 0;
 
diff --git a/include/bw_dist.h b/include/bw_dist.h
index c4035cc..322a098 100644
--- a/include/bw_dist.h
+++ b/include/bw_dist.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_clip bw_common bw_gain bw_hp1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Adjusted internal peak cutoff to more sensible value.</li>
@@ -140,7 +145,7 @@ static inline void bw_dist_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_dist_update_coeffs_ctrl()
  *  ```>>> */
@@ -253,8 +258,8 @@ static inline char bw_dist_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_dist_state`.
@@ -321,7 +326,7 @@ struct bw_dist_state {
 
 static inline void bw_dist_init(
 		bw_dist_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_hp1_init(&coeffs->hp1_coeffs);
 	bw_peak_init(&coeffs->peak_coeffs);
@@ -351,7 +356,7 @@ static inline void bw_dist_init(
 static inline void bw_dist_set_sample_rate(
 		bw_dist_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -375,7 +380,7 @@ static inline void bw_dist_set_sample_rate(
 
 static inline void bw_dist_reset_coeffs(
 		bw_dist_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_set_sample_rate);
 
@@ -395,10 +400,10 @@ static inline float bw_dist_reset_state(
 		const bw_dist_coeffs * BW_RESTRICT coeffs,
 		bw_dist_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float y = bw_hp1_reset_state(&coeffs->hp1_coeffs, &state->hp1_state, x_0);
@@ -426,18 +431,18 @@ static inline void bw_dist_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_dist_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -446,12 +451,12 @@ static inline void bw_dist_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_dist_update_coeffs_ctrl(
 		bw_dist_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
 
@@ -465,7 +470,7 @@ static inline void bw_dist_update_coeffs_ctrl(
 
 static inline void bw_dist_update_coeffs_audio(
 		bw_dist_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
 
@@ -481,10 +486,10 @@ static inline float bw_dist_process1(
 		const bw_dist_coeffs * BW_RESTRICT coeffs,
 		bw_dist_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -509,14 +514,14 @@ static inline void bw_dist_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_dist_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -537,17 +542,17 @@ static inline void bw_dist_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -568,7 +573,7 @@ static inline void bw_dist_process_multi(
 static inline void bw_dist_set_distortion(
 		bw_dist_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -583,7 +588,7 @@ static inline void bw_dist_set_distortion(
 static inline void bw_dist_set_tone(
 		bw_dist_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -598,7 +603,7 @@ static inline void bw_dist_set_tone(
 static inline void bw_dist_set_volume(
 		bw_dist_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -612,7 +617,7 @@ static inline void bw_dist_set_volume(
 
 static inline char bw_dist_coeffs_is_valid(
 		const bw_dist_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_dist_coeffs"))
@@ -632,21 +637,21 @@ static inline char bw_dist_coeffs_is_valid(
 static inline char bw_dist_state_is_valid(
 		const bw_dist_coeffs * BW_RESTRICT coeffs,
 		const bw_dist_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_dist_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_coeffs : NULL, &state->hp1_state)
-		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : NULL, &state->peak_state)
-		&& bw_clip_state_is_valid(coeffs ? &coeffs->clip_coeffs : NULL, &state->clip_state)
-		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : NULL, &state->satur_state)
-		&& bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : NULL, &state->lp1_state);
+	return bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_coeffs : BW_NULL, &state->hp1_state)
+		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : BW_NULL, &state->peak_state)
+		&& bw_clip_state_is_valid(coeffs ? &coeffs->clip_coeffs : BW_NULL, &state->clip_state)
+		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : BW_NULL, &state->satur_state)
+		&& bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_drive.h b/include/bw_drive.h
index d6876f9..6c91684 100644
--- a/include/bw_drive.h
+++ b/include/bw_drive.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_common bw_gain bw_hs1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Improved algorithm to be a bit more faithful to the
@@ -141,7 +146,7 @@ static inline void bw_drive_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_drive_update_coeffs_ctrl()
  *  ```>>> */
@@ -254,8 +259,8 @@ static inline char bw_drive_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_drive_state`.
@@ -322,7 +327,7 @@ struct bw_drive_state {
 
 static inline void bw_drive_init(
 		bw_drive_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->hp2_coeffs);
 	bw_hs1_init(&coeffs->hs1_coeffs);
@@ -352,7 +357,7 @@ static inline void bw_drive_init(
 static inline void bw_drive_set_sample_rate(
 		bw_drive_coeffs * BW_RESTRICT coeffs,
 		float                         sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -376,7 +381,7 @@ static inline void bw_drive_set_sample_rate(
 
 static inline void bw_drive_reset_coeffs(
 		bw_drive_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_set_sample_rate);
 
@@ -396,10 +401,10 @@ static inline float bw_drive_reset_state(
 		const bw_drive_coeffs * BW_RESTRICT coeffs,
 		bw_drive_state * BW_RESTRICT        state,
 		float                               x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float v_lp, v_hp, v_bp;
@@ -428,18 +433,18 @@ static inline void bw_drive_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_drive_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -448,12 +453,12 @@ static inline void bw_drive_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_drive_update_coeffs_ctrl(
 		bw_drive_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
 
@@ -467,7 +472,7 @@ static inline void bw_drive_update_coeffs_ctrl(
 
 static inline void bw_drive_update_coeffs_audio(
 		bw_drive_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
 
@@ -483,10 +488,10 @@ static inline float bw_drive_process1(
 		const bw_drive_coeffs * BW_RESTRICT coeffs,
 		bw_drive_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -512,14 +517,14 @@ static inline void bw_drive_process(
 		const float *                 x,
 		float *                       y,
 		size_t                        n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_drive_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -540,17 +545,17 @@ static inline void bw_drive_process_multi(
 		float * const *                                  y,
 		size_t                                           n_channels,
 		size_t                                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -571,7 +576,7 @@ static inline void bw_drive_process_multi(
 static inline void bw_drive_set_drive(
 		bw_drive_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -586,7 +591,7 @@ static inline void bw_drive_set_drive(
 static inline void bw_drive_set_tone(
 		bw_drive_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -601,7 +606,7 @@ static inline void bw_drive_set_tone(
 static inline void bw_drive_set_volume(
 		bw_drive_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -615,7 +620,7 @@ static inline void bw_drive_set_volume(
 
 static inline char bw_drive_coeffs_is_valid(
 		const bw_drive_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_drive_coeffs"))
@@ -635,21 +640,21 @@ static inline char bw_drive_coeffs_is_valid(
 static inline char bw_drive_state_is_valid(
 		const bw_drive_coeffs * BW_RESTRICT coeffs,
 		const bw_drive_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_drive_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->hp2_coeffs : NULL, &state->hp2_state)
-		&& bw_hs1_state_is_valid(coeffs ? &coeffs->hs1_coeffs : NULL, &state->hs1_state)
-		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : NULL, &state->peak_state)
-		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : NULL, &state->satur_state)
-		&& bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : NULL, &state->lp1_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->hp2_coeffs : BW_NULL, &state->hp2_state)
+		&& bw_hs1_state_is_valid(coeffs ? &coeffs->hs1_coeffs : BW_NULL, &state->hs1_state)
+		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : BW_NULL, &state->peak_state)
+		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : BW_NULL, &state->satur_state)
+		&& bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_dry_wet.h b/include/bw_dry_wet.h
index 188bb26..9c76443 100644
--- a/include/bw_dry_wet.h
+++ b/include/bw_dry_wet.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole }}}
  *  description {{{
  *    Dry/wet mixer.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Module renamed as bw_dry_wet.</li>
@@ -220,7 +225,7 @@ struct bw_dry_wet_coeffs {
 
 static inline void bw_dry_wet_init(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_gain_init(&coeffs->gain_coeffs);
 
@@ -235,7 +240,7 @@ static inline void bw_dry_wet_init(
 static inline void bw_dry_wet_set_sample_rate(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs,
 		float                           sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -251,7 +256,7 @@ static inline void bw_dry_wet_set_sample_rate(
 
 static inline void bw_dry_wet_reset_coeffs(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_set_sample_rate);
 
@@ -266,7 +271,7 @@ static inline void bw_dry_wet_reset_coeffs(
 
 static inline void bw_dry_wet_update_coeffs_ctrl(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_reset_coeffs);
 
@@ -278,7 +283,7 @@ static inline void bw_dry_wet_update_coeffs_ctrl(
 
 static inline void bw_dry_wet_update_coeffs_audio(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_reset_coeffs);
 
@@ -292,7 +297,7 @@ static inline float bw_dry_wet_process1(
 		const bw_dry_wet_coeffs * BW_RESTRICT coeffs,
 		float                                 x_dry,
 		float                                 x_wet) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x_dry));
@@ -313,14 +318,14 @@ static inline void bw_dry_wet_process(
 		const float *                   x_wet,
 		float *                         y,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_dry != NULL);
+	BW_ASSERT(x_dry != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_dry, n_samples));
-	BW_ASSERT(x_wet != NULL);
+	BW_ASSERT(x_wet != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_wet, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_dry_wet_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -340,12 +345,12 @@ static inline void bw_dry_wet_process_multi(
 		float * const *                 y,
 		size_t                          n_channels,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_dry != NULL);
-	BW_ASSERT(x_wet != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x_dry != BW_NULL);
+	BW_ASSERT(x_wet != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -366,7 +371,7 @@ static inline void bw_dry_wet_process_multi(
 static inline void bw_dry_wet_set_wet(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -381,7 +386,7 @@ static inline void bw_dry_wet_set_wet(
 static inline void bw_dry_wet_set_smooth_tau(
 		bw_dry_wet_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_dry_wet_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_dry_wet_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -395,7 +400,7 @@ static inline void bw_dry_wet_set_smooth_tau(
 
 static inline char bw_dry_wet_coeffs_is_valid(
 		const bw_dry_wet_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_dry_wet_coeffs"))
diff --git a/include/bw_env_follow.h b/include/bw_env_follow.h
index 9a091ff..64e0950 100644
--- a/include/bw_env_follow.h
+++ b/include/bw_env_follow.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Envelope follower made of a full-wave rectifier followed by
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input value to
@@ -151,7 +156,7 @@ static inline void bw_env_follow_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_env_follow_update_coeffs_ctrl()
  *  ```>>> */
@@ -190,7 +195,7 @@ static inline void bw_env_follow_process(
  *    first `n_samples` of the output buffer `y`, while using and updating both
  *    `coeffs` and `state` (control and audio rate).
  *
- *    `y` may be `NULL`.
+ *    `y` may be `BW_NULL`.
  *
  *    #### bw_env_follow_process_multi()
  *  ```>>> */
@@ -207,7 +212,7 @@ static inline void bw_env_follow_process_multi(
  *    using and updating both the common `coeffs` and each of the `n_channels`
  *    `state`s (control and audio rate).
  *
- *    `y` or any element of `y` may be `NULL`.
+ *    `y` or any element of `y` may be `BW_NULL`.
  *
  *    #### bw_env_follow_set_attack_tau()
  *  ```>>> */
@@ -264,8 +269,8 @@ static inline char bw_env_follow_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_env_follow_state`.
@@ -319,7 +324,7 @@ struct bw_env_follow_state {
 
 static inline void bw_env_follow_init(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->one_pole_coeffs);
 
@@ -335,7 +340,7 @@ static inline void bw_env_follow_init(
 static inline void bw_env_follow_set_sample_rate(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		float                              sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -351,7 +356,7 @@ static inline void bw_env_follow_set_sample_rate(
 
 static inline void bw_env_follow_reset_coeffs(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_set_sample_rate);
 
@@ -369,10 +374,10 @@ static inline float bw_env_follow_reset_state(
 		const bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		bw_env_follow_state * BW_RESTRICT        state,
 		float                                    x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float x = bw_absf(x_0);
@@ -396,18 +401,18 @@ static inline void bw_env_follow_reset_state_multi(
 		const float *                                         x_0,
 		float *                                               y_0,
 		size_t                                                n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_env_follow_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -416,12 +421,12 @@ static inline void bw_env_follow_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_env_follow_update_coeffs_ctrl(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 
@@ -433,7 +438,7 @@ static inline void bw_env_follow_update_coeffs_ctrl(
 
 static inline void bw_env_follow_update_coeffs_audio(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 
@@ -447,10 +452,10 @@ static inline float bw_env_follow_process1(
 		const bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		bw_env_follow_state * BW_RESTRICT        state,
 		float                                    x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -471,16 +476,16 @@ static inline void bw_env_follow_process(
 		const float *                      x,
 		float *                            y,
 		size_t                             n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
 
 	bw_env_follow_update_coeffs_ctrl(coeffs);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++) {
 			bw_env_follow_update_coeffs_audio(coeffs);
 			y[i] = bw_env_follow_process1(coeffs, state, x[i]);
@@ -494,7 +499,7 @@ static inline void bw_env_follow_process(
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_env_follow_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
 }
 
 static inline void bw_env_follow_process_multi(
@@ -504,30 +509,30 @@ static inline void bw_env_follow_process_multi(
 		float * const *                                       y,
 		size_t                                                n_channels,
 		size_t                                                n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
+				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 #endif
 
 	bw_env_follow_update_coeffs_ctrl(coeffs);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++) {
 			bw_env_follow_update_coeffs_audio(coeffs);
 			for (size_t j = 0; j < n_channels; j++) {
 				const float v = bw_env_follow_process1(coeffs, state[j], x[j][i]);
-				if (y[j] != NULL)
+				if (y[j] != BW_NULL)
 					y[j][i] = v;
 			}
 		}
@@ -545,7 +550,7 @@ static inline void bw_env_follow_process_multi(
 static inline void bw_env_follow_set_attack_tau(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -560,7 +565,7 @@ static inline void bw_env_follow_set_attack_tau(
 static inline void bw_env_follow_set_release_tau(
 		bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -574,15 +579,15 @@ static inline void bw_env_follow_set_release_tau(
 
 static inline float bw_env_follow_get_y_z1(
 		const bw_env_follow_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_env_follow_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_env_follow_state_is_valid(BW_NULL, state));
 
 	return bw_one_pole_get_y_z1(&state->one_pole_state);
 }
 
 static inline char bw_env_follow_coeffs_is_valid(
 		const bw_env_follow_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_env_follow_coeffs"))
@@ -597,17 +602,17 @@ static inline char bw_env_follow_coeffs_is_valid(
 static inline char bw_env_follow_state_is_valid(
 		const bw_env_follow_coeffs * BW_RESTRICT coeffs,
 		const bw_env_follow_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_env_follow_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_one_pole_state_is_valid(coeffs ? &coeffs->one_pole_coeffs : NULL, &state->one_pole_state);
+	return bw_one_pole_state_is_valid(coeffs ? &coeffs->one_pole_coeffs : BW_NULL, &state->one_pole_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_env_gen.h b/include/bw_env_gen.h
index 57a3c7f..5c8a1c1 100644
--- a/include/bw_env_gen.h
+++ b/include/bw_env_gen.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -43,6 +43,7 @@
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Added skip_sustain and always_reach_sustain parameters.</li>
+ *          <li>Now using <code>BW_NULL</code>.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>1.0.0</strong>:
@@ -200,7 +201,7 @@ static inline void bw_env_gen_reset_state_multi(
  *    non-`0` for on) in the `gate_0` array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_env_gen_update_coeffs_ctrl()
  *  ```>>> */
@@ -248,7 +249,7 @@ static inline void bw_env_gen_process(
  *    the given `gate` value (`0` for off, non-`0` for on), while using and
  *    updating both `coeffs` and `state` (control and audio rate).
  *
- *    `y` may be `NULL`.
+ *    `y` may be `BW_NULL`.
  *
  *    #### bw_env_gen_process_multi()
  *  ```>>> */
@@ -265,7 +266,7 @@ static inline void bw_env_gen_process_multi(
  *    non-`0` for on), while using and updating both the common `coeffs` and
  *    each of the `n_channels` `state`s (control and audio rate).
  *
- *    `y` or any element of `y` may be `NULL`.
+ *    `y` or any element of `y` may be `BW_NULL`.
  *
  *    #### bw_env_gen_set_attack()
  *  ```>>> */
@@ -372,8 +373,8 @@ static inline char bw_env_gen_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_env_gen_state`.
@@ -452,7 +453,7 @@ struct bw_env_gen_state {
 
 static inline void bw_env_gen_init(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.05f);
@@ -475,7 +476,7 @@ static inline void bw_env_gen_init(
 static inline void bw_env_gen_set_sample_rate(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		float                           sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -509,7 +510,7 @@ static inline void bw_env_gen_do_update_coeffs_ctrl(
 
 static inline void bw_env_gen_reset_coeffs(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_set_sample_rate);
 
@@ -528,10 +529,10 @@ static inline float bw_env_gen_reset_state(
 		const bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		bw_env_gen_state * BW_RESTRICT        state,
 		char                                  gate_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 	bw_one_pole_reset_state(&coeffs->smooth_coeffs, &state->smooth_state, coeffs->sustain);
 	if (gate_0) {
@@ -561,18 +562,18 @@ static inline void bw_env_gen_reset_state_multi(
 		const char * BW_RESTRICT                           gate_0,
 		float * BW_RESTRICT                                y_0,
 		size_t                                             n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(gate_0 != NULL);
+	BW_ASSERT(gate_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_env_gen_reset_state(coeffs, state[i], gate_0[i]);
 	else
@@ -581,12 +582,12 @@ static inline void bw_env_gen_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_env_gen_update_coeffs_ctrl(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
 
@@ -598,7 +599,7 @@ static inline void bw_env_gen_update_coeffs_ctrl(
 
 static inline void bw_env_gen_update_coeffs_audio(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
 
@@ -609,10 +610,10 @@ static inline void bw_env_gen_process_ctrl(
 		const bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		bw_env_gen_state * BW_RESTRICT        state,
 		char                                  gate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(coeffs, state));
 
 	if (gate) {
@@ -631,10 +632,10 @@ static inline void bw_env_gen_process_ctrl(
 static inline float bw_env_gen_process1(
 		const bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		bw_env_gen_state * BW_RESTRICT        state) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(coeffs, state));
 
 	uint32_t v = 0;
@@ -686,15 +687,15 @@ static inline void bw_env_gen_process(
 		char                            gate,
 		float * BW_RESTRICT             y,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(coeffs, state));
 
 	bw_env_gen_update_coeffs_ctrl(coeffs);
 	bw_env_gen_process_ctrl(coeffs, state, gate);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++)
 			y[i] = bw_env_gen_process1(coeffs, state);
 	else
@@ -704,7 +705,7 @@ static inline void bw_env_gen_process(
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
 }
 
 static inline void bw_env_gen_process_multi(
@@ -714,31 +715,31 @@ static inline void bw_env_gen_process_multi(
 		float * BW_RESTRICT const * BW_RESTRICT            y,
 		size_t                                             n_channels,
 		size_t                                             n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(gate != NULL);
+	BW_ASSERT(gate != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
+				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 #endif
 
 	bw_env_gen_update_coeffs_ctrl(coeffs);
 	for (size_t j = 0; j < n_channels; j++)
 		bw_env_gen_process_ctrl(coeffs, state[j], gate[j]);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++)
 			for (size_t j = 0; j < n_channels; j++) {
 				const float v = bw_env_gen_process1(coeffs, state[j]);
-				if (y[j] != NULL)
+				if (y[j] != BW_NULL)
 					y[j][i] = v;
 			}
 	else
@@ -753,7 +754,7 @@ static inline void bw_env_gen_process_multi(
 static inline void bw_env_gen_set_attack(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -774,7 +775,7 @@ static inline void bw_env_gen_set_attack(
 static inline void bw_env_gen_set_decay(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -795,7 +796,7 @@ static inline void bw_env_gen_set_decay(
 static inline void bw_env_gen_set_sustain(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -816,7 +817,7 @@ static inline void bw_env_gen_set_sustain(
 static inline void bw_env_gen_set_release(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -837,7 +838,7 @@ static inline void bw_env_gen_set_release(
 static inline void bw_env_gen_set_skip_sustain(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		char                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 
@@ -850,7 +851,7 @@ static inline void bw_env_gen_set_skip_sustain(
 static inline void bw_env_gen_set_always_reach_sustain(
 		bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		char                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_env_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_env_gen_coeffs_state_init);
 
@@ -862,16 +863,16 @@ static inline void bw_env_gen_set_always_reach_sustain(
 
 static inline bw_env_gen_phase bw_env_gen_get_phase(
 		const bw_env_gen_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(BW_NULL, state));
 
 	return state->phase;
 }
 
 static inline float bw_env_gen_get_y_z1(
 		const bw_env_gen_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_env_gen_state_is_valid(BW_NULL, state));
 
 	const float y = (1.f / (float)BW_ENV_V_MAX) * state->v;
 
@@ -882,7 +883,7 @@ static inline float bw_env_gen_get_y_z1(
 
 static inline char bw_env_gen_coeffs_is_valid(
 		const bw_env_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_env_gen_coeffs"))
@@ -911,18 +912,18 @@ static inline char bw_env_gen_coeffs_is_valid(
 static inline char bw_env_gen_state_is_valid(
 		const bw_env_gen_coeffs * BW_RESTRICT coeffs,
 		const bw_env_gen_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_env_gen_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
 	return state->phase >= bw_env_gen_phase_off && state->phase <= bw_env_gen_phase_release
-		&& bw_one_pole_state_is_valid(coeffs ? &coeffs->smooth_coeffs : NULL, &state->smooth_state);
+		&& bw_one_pole_state_is_valid(coeffs ? &coeffs->smooth_coeffs : BW_NULL, &state->smooth_state);
 }
 
 #undef BW_ENV_GEN_PARAM_ATTACK
diff --git a/include/bw_fuzz.h b/include/bw_fuzz.h
index adfe317..33abe47 100644
--- a/include/bw_fuzz.h
+++ b/include/bw_fuzz.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_common bw_gain bw_hp1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Improved algorithm to be a bit more faithful to the
@@ -141,7 +146,7 @@ static inline void bw_fuzz_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_fuzz_update_coeffs_ctrl()
  *  ```>>> */
@@ -242,8 +247,8 @@ static inline char bw_fuzz_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_fuzz_state`.
@@ -311,7 +316,7 @@ struct bw_fuzz_state {
 
 static inline void bw_fuzz_init(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_hp1_init(&coeffs->hp1_in_coeffs);
 	bw_svf_init(&coeffs->lp2_coeffs);
@@ -338,7 +343,7 @@ static inline void bw_fuzz_init(
 static inline void bw_fuzz_set_sample_rate(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -363,7 +368,7 @@ static inline void bw_fuzz_set_sample_rate(
 
 static inline void bw_fuzz_reset_coeffs(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_set_sample_rate);
 
@@ -382,10 +387,10 @@ static inline float bw_fuzz_reset_state(
 		const bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		bw_fuzz_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float y = bw_hp1_reset_state(&coeffs->hp1_in_coeffs, &state->hp1_in_state, x_0);
@@ -415,18 +420,18 @@ static inline void bw_fuzz_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_fuzz_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -435,12 +440,12 @@ static inline void bw_fuzz_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_fuzz_update_coeffs_ctrl(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
 
@@ -453,7 +458,7 @@ static inline void bw_fuzz_update_coeffs_ctrl(
 
 static inline void bw_fuzz_update_coeffs_audio(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
 
@@ -468,10 +473,10 @@ static inline float bw_fuzz_process1(
 		const bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		bw_fuzz_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -498,14 +503,14 @@ static inline void bw_fuzz_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_fuzz_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -526,17 +531,17 @@ static inline void bw_fuzz_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -557,7 +562,7 @@ static inline void bw_fuzz_process_multi(
 static inline void bw_fuzz_set_fuzz(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -572,7 +577,7 @@ static inline void bw_fuzz_set_fuzz(
 static inline void bw_fuzz_set_volume(
 		bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_fuzz_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_fuzz_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -586,7 +591,7 @@ static inline void bw_fuzz_set_volume(
 
 static inline char bw_fuzz_coeffs_is_valid(
 		const bw_fuzz_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_fuzz_coeffs"))
@@ -606,22 +611,22 @@ static inline char bw_fuzz_coeffs_is_valid(
 static inline char bw_fuzz_state_is_valid(
 		const bw_fuzz_coeffs * BW_RESTRICT coeffs,
 		const bw_fuzz_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_fuzz_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_in_coeffs : NULL, &state->hp1_in_state)
-		&& bw_svf_state_is_valid(coeffs ? &coeffs->lp2_coeffs : NULL, &state->lp2_1_state)
-		&& bw_svf_state_is_valid(coeffs ? &coeffs->lp2_coeffs : NULL, &state->lp2_2_state)
-		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : NULL, &state->peak_state)
-		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : NULL, &state->satur_state)
-		&& bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_out_coeffs : NULL, &state->hp1_out_state);
+	return bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_in_coeffs : BW_NULL, &state->hp1_in_state)
+		&& bw_svf_state_is_valid(coeffs ? &coeffs->lp2_coeffs : BW_NULL, &state->lp2_1_state)
+		&& bw_svf_state_is_valid(coeffs ? &coeffs->lp2_coeffs : BW_NULL, &state->lp2_2_state)
+		&& bw_peak_state_is_valid(coeffs ? &coeffs->peak_coeffs : BW_NULL, &state->peak_state)
+		&& bw_satur_state_is_valid(coeffs ? &coeffs->satur_coeffs : BW_NULL, &state->satur_state)
+		&& bw_hp1_state_is_valid(coeffs ? &coeffs->hp1_out_coeffs : BW_NULL, &state->hp1_out_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_gain.h b/include/bw_gain.h
index 9d47c05..8b3424f 100644
--- a/include/bw_gain.h
+++ b/include/bw_gain.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_gain_get_gain_lin()</code>.</li>
@@ -272,7 +277,7 @@ struct bw_gain_coeffs {
 
 static inline void bw_gain_init(
 		bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.05f);
@@ -289,7 +294,7 @@ static inline void bw_gain_init(
 static inline void bw_gain_set_sample_rate(
 		bw_gain_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -305,7 +310,7 @@ static inline void bw_gain_set_sample_rate(
 
 static inline void bw_gain_reset_coeffs(
 		bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_set_sample_rate);
 
@@ -321,7 +326,7 @@ static inline void bw_gain_reset_coeffs(
 
 static inline void bw_gain_update_coeffs_ctrl(
 		bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
 
@@ -333,7 +338,7 @@ static inline void bw_gain_update_coeffs_ctrl(
 
 static inline void bw_gain_update_coeffs_audio(
 		bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
 
@@ -347,7 +352,7 @@ static inline void bw_gain_update_coeffs_audio(
 static inline float bw_gain_process1(
 		const bw_gain_coeffs * BW_RESTRICT coeffs,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -366,12 +371,12 @@ static inline void bw_gain_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_gain_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -390,11 +395,11 @@ static inline void bw_gain_process_multi(
 		float * const *              y,
 		size_t                       n_channels,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -415,7 +420,7 @@ static inline void bw_gain_process_multi(
 static inline void bw_gain_set_gain_lin(
 		bw_gain_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -429,7 +434,7 @@ static inline void bw_gain_set_gain_lin(
 static inline void bw_gain_set_gain_dB(
 		bw_gain_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -444,7 +449,7 @@ static inline void bw_gain_set_gain_dB(
 static inline void bw_gain_set_smooth_tau(
 		bw_gain_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -458,7 +463,7 @@ static inline void bw_gain_set_smooth_tau(
 
 static inline float bw_gain_get_gain_lin(
 		const bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 
 	return coeffs->gain;
@@ -466,7 +471,7 @@ static inline float bw_gain_get_gain_lin(
 
 static inline float bw_gain_get_gain_cur(
 		const bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_gain_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_gain_coeffs_state_reset_coeffs);
 
@@ -475,7 +480,7 @@ static inline float bw_gain_get_gain_cur(
 
 static inline char bw_gain_coeffs_is_valid(
 		const bw_gain_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_gain_coeffs"))
diff --git a/include/bw_hp1.h b/include/bw_hp1.h
index c12c2a1..a02da0d 100644
--- a/include/bw_hp1.h
+++ b/include/bw_hp1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order highpass filter (6 dB/oct) with gain asymptotically
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_hp1_reset_state_multi()</code> and updated C++
@@ -146,7 +151,7 @@ static inline void bw_hp1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_hp1_update_coeffs_ctrl()
  *  ```>>> */
@@ -260,8 +265,8 @@ static inline char bw_hp1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_hp1_state`.
@@ -314,7 +319,7 @@ struct bw_hp1_state {
 
 static inline void bw_hp1_init(
 		bw_hp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_lp1_init(&coeffs->lp1_coeffs);
 
@@ -330,7 +335,7 @@ static inline void bw_hp1_init(
 static inline void bw_hp1_set_sample_rate(
 		bw_hp1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -346,7 +351,7 @@ static inline void bw_hp1_set_sample_rate(
 
 static inline void bw_hp1_reset_coeffs(
 		bw_hp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_set_sample_rate);
 
@@ -364,10 +369,10 @@ static inline float bw_hp1_reset_state(
 		const bw_hp1_coeffs * BW_RESTRICT coeffs,
 		bw_hp1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float lp = bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, x_0);
@@ -391,31 +396,31 @@ static inline void bw_hp1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
 	for (size_t i = 0; i < n_channels; i++)
 		bw_hp1_reset_state(coeffs, state[i], x_0[i]);
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = 0.f;
 
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_hp1_update_coeffs_ctrl(
 		bw_hp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
 
@@ -427,7 +432,7 @@ static inline void bw_hp1_update_coeffs_ctrl(
 
 static inline void bw_hp1_update_coeffs_audio(
 		bw_hp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
 
@@ -441,10 +446,10 @@ static inline float bw_hp1_process1(
 		const bw_hp1_coeffs * BW_RESTRICT coeffs,
 		bw_hp1_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -465,14 +470,14 @@ static inline void bw_hp1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_hp1_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -493,17 +498,17 @@ static inline void bw_hp1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -524,7 +529,7 @@ static inline void bw_hp1_process_multi(
 static inline void bw_hp1_set_cutoff(
 		bw_hp1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -539,7 +544,7 @@ static inline void bw_hp1_set_cutoff(
 static inline void bw_hp1_set_prewarp_at_cutoff(
 		bw_hp1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_init);
 
@@ -552,7 +557,7 @@ static inline void bw_hp1_set_prewarp_at_cutoff(
 static inline void bw_hp1_set_prewarp_freq(
 		bw_hp1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -566,7 +571,7 @@ static inline void bw_hp1_set_prewarp_freq(
 
 static inline char bw_hp1_coeffs_is_valid(
 		const bw_hp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_hp1_coeffs"))
@@ -581,17 +586,17 @@ static inline char bw_hp1_coeffs_is_valid(
 static inline char bw_hp1_state_is_valid(
 		const bw_hp1_coeffs * BW_RESTRICT coeffs,
 		const bw_hp1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_hp1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : NULL, &state->lp1_state);
+	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_hs1.h b/include/bw_hs1.h
index 263faa7..846c756 100644
--- a/include/bw_hs1.h
+++ b/include/bw_hs1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_mm1 bw_one_pole }}}
  *  description {{{
  *    First-order high shelf filter (6 dB/oct) with unitary DC gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_hs1_reset_state_multi()</code> and updated C++
@@ -147,7 +152,7 @@ static inline void bw_hs1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_hs1_update_coeffs_ctrl()
  *  ```>>> */
@@ -302,8 +307,8 @@ static inline char bw_hs1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_hs1_state`.
@@ -364,7 +369,7 @@ struct bw_hs1_state {
 
 static inline void bw_hs1_init(
 		bw_hs1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_mm1_init(&coeffs->mm1_coeffs);
 	bw_mm1_set_prewarp_at_cutoff(&coeffs->mm1_coeffs, 0);
@@ -387,7 +392,7 @@ static inline void bw_hs1_init(
 static inline void bw_hs1_set_sample_rate(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -414,7 +419,7 @@ static inline void bw_hs1_update_mm1_params(
 
 static inline void bw_hs1_reset_coeffs(
 		bw_hs1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
@@ -435,10 +440,10 @@ static inline float bw_hs1_reset_state(
 		const bw_hs1_coeffs * BW_RESTRICT coeffs,
 		bw_hs1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float y = bw_mm1_reset_state(&coeffs->mm1_coeffs, &state->mm1_state, x_0);
@@ -461,18 +466,18 @@ static inline void bw_hs1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_hs1_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -481,12 +486,12 @@ static inline void bw_hs1_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_hs1_update_coeffs_ctrl(
 		bw_hs1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
@@ -500,7 +505,7 @@ static inline void bw_hs1_update_coeffs_ctrl(
 
 static inline void bw_hs1_update_coeffs_audio(
 		bw_hs1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
@@ -515,11 +520,11 @@ static inline float bw_hs1_process1(
 		const bw_hs1_coeffs * BW_RESTRICT coeffs,
 		bw_hs1_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -539,15 +544,15 @@ static inline void bw_hs1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_hs1_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -568,18 +573,18 @@ static inline void bw_hs1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(coeffs->high_gain) >= 1e-6f && coeffs->cutoff * bw_sqrtf(coeffs->high_gain) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -600,7 +605,7 @@ static inline void bw_hs1_process_multi(
 static inline void bw_hs1_set_cutoff(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -618,7 +623,7 @@ static inline void bw_hs1_set_cutoff(
 static inline void bw_hs1_set_prewarp_at_cutoff(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 
@@ -631,7 +636,7 @@ static inline void bw_hs1_set_prewarp_at_cutoff(
 static inline void bw_hs1_set_prewarp_freq(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -646,7 +651,7 @@ static inline void bw_hs1_set_prewarp_freq(
 static inline void bw_hs1_set_high_gain_lin(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -664,7 +669,7 @@ static inline void bw_hs1_set_high_gain_lin(
 static inline void bw_hs1_set_high_gain_dB(
 		bw_hs1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -678,7 +683,7 @@ static inline void bw_hs1_set_high_gain_dB(
 
 static inline char bw_hs1_coeffs_is_valid(
 		const bw_hs1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_hs1_coeffs"))
@@ -702,17 +707,17 @@ static inline char bw_hs1_coeffs_is_valid(
 static inline char bw_hs1_state_is_valid(
 		const bw_hs1_coeffs * BW_RESTRICT coeffs,
 		const bw_hs1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_hs1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_mm1_state_is_valid(coeffs ? &coeffs->mm1_coeffs : NULL, &state->mm1_state);
+	return bw_mm1_state_is_valid(coeffs ? &coeffs->mm1_coeffs : BW_NULL, &state->mm1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_hs2.h b/include/bw_hs2.h
index 3ebdbd8..c166564 100644
--- a/include/bw_hs2.h
+++ b/include/bw_hs2.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_mm2 bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order high shelf filter (12 dB/oct) with unitary DC gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_hs2_reset_state_multi()</code> and updated C++
@@ -149,7 +154,7 @@ static inline void bw_hs2_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_hs2_update_coeffs_ctrl()
  *  ```>>> */
@@ -316,8 +321,8 @@ static inline char bw_hs2_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_hs2_state`.
@@ -385,7 +390,7 @@ struct bw_hs2_state {
 
 static inline void bw_hs2_init(
 		bw_hs2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_mm2_init(&coeffs->mm2_coeffs);
 	bw_mm2_set_prewarp_at_cutoff(&coeffs->mm2_coeffs, 0);
@@ -406,7 +411,7 @@ static inline void bw_hs2_init(
 static inline void bw_hs2_set_sample_rate(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -438,7 +443,7 @@ static inline void bw_hs2_update_mm2_params(
 
 static inline void bw_hs2_reset_coeffs(
 		bw_hs2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
@@ -459,10 +464,10 @@ static inline float bw_hs2_reset_state(
 		const bw_hs2_coeffs * BW_RESTRICT coeffs,
 		bw_hs2_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float y = bw_mm2_reset_state(&coeffs->mm2_coeffs, &state->mm2_state, x_0);
@@ -485,18 +490,18 @@ static inline void bw_hs2_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_hs2_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -505,12 +510,12 @@ static inline void bw_hs2_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_hs2_update_coeffs_ctrl(
 		bw_hs2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
@@ -524,7 +529,7 @@ static inline void bw_hs2_update_coeffs_ctrl(
 
 static inline void bw_hs2_update_coeffs_audio(
 		bw_hs2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
@@ -539,11 +544,11 @@ static inline float bw_hs2_process1(
 		const bw_hs2_coeffs * BW_RESTRICT coeffs,
 		bw_hs2_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -563,15 +568,15 @@ static inline void bw_hs2_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_hs2_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -592,18 +597,18 @@ static inline void bw_hs2_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) >= 1e-6f && coeffs->cutoff * bw_sqrtf(bw_sqrtf(coeffs->high_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -624,7 +629,7 @@ static inline void bw_hs2_process_multi(
 static inline void bw_hs2_set_cutoff(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -645,7 +650,7 @@ static inline void bw_hs2_set_cutoff(
 static inline void bw_hs2_set_Q(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -660,7 +665,7 @@ static inline void bw_hs2_set_Q(
 static inline void bw_hs2_set_prewarp_at_cutoff(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 
@@ -673,7 +678,7 @@ static inline void bw_hs2_set_prewarp_at_cutoff(
 static inline void bw_hs2_set_prewarp_freq(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -688,7 +693,7 @@ static inline void bw_hs2_set_prewarp_freq(
 static inline void bw_hs2_set_high_gain_lin(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -709,7 +714,7 @@ static inline void bw_hs2_set_high_gain_lin(
 static inline void bw_hs2_set_high_gain_dB(
 		bw_hs2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_hs2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_hs2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -723,7 +728,7 @@ static inline void bw_hs2_set_high_gain_dB(
 
 static inline char bw_hs2_coeffs_is_valid(
 		const bw_hs2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_hs2_coeffs"))
@@ -756,17 +761,17 @@ static inline char bw_hs2_coeffs_is_valid(
 static inline char bw_hs2_state_is_valid(
 		const bw_hs2_coeffs * BW_RESTRICT coeffs,
 		const bw_hs2_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_hs2_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : NULL, &state->mm2_state);
+	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : BW_NULL, &state->mm2_state);
 }
 
 #undef BW_HS2_PARAM_CUTOFF
diff --git a/include/bw_lp1.h b/include/bw_lp1.h
index 8b5f3af..b254342 100644
--- a/include/bw_lp1.h
+++ b/include/bw_lp1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    First-order lowpass filter (6 dB/oct) with unitary DC gain.
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Limited actual prewarping frequency to prevent instability.</li>
@@ -147,7 +152,7 @@ static inline void bw_lp1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_lp1_update_coeffs_ctrl()
  *  ```>>> */
@@ -261,8 +266,8 @@ static inline char bw_lp1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_lp1_state`.
@@ -332,7 +337,7 @@ struct bw_lp1_state {
 
 static inline void bw_lp1_init(
 		bw_lp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -353,7 +358,7 @@ static inline void bw_lp1_init(
 static inline void bw_lp1_set_sample_rate(
 		bw_lp1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -394,7 +399,7 @@ static inline void bw_lp1_do_update_coeffs(
 
 static inline void bw_lp1_reset_coeffs(
 		bw_lp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_set_sample_rate);
 
@@ -414,10 +419,10 @@ static inline float bw_lp1_reset_state(
 		const bw_lp1_coeffs * BW_RESTRICT coeffs,
 		bw_lp1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	(void)coeffs;
@@ -443,18 +448,18 @@ static inline void bw_lp1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_lp1_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -463,12 +468,12 @@ static inline void bw_lp1_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_lp1_update_coeffs_ctrl(
 		bw_lp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
 
@@ -477,7 +482,7 @@ static inline void bw_lp1_update_coeffs_ctrl(
 
 static inline void bw_lp1_update_coeffs_audio(
 		bw_lp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
 
@@ -491,10 +496,10 @@ static inline float bw_lp1_process1(
 		const bw_lp1_coeffs * BW_RESTRICT coeffs,
 		bw_lp1_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -517,14 +522,14 @@ static inline void bw_lp1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_lp1_update_coeffs_audio(coeffs);
@@ -544,17 +549,17 @@ static inline void bw_lp1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -574,7 +579,7 @@ static inline void bw_lp1_process_multi(
 static inline void bw_lp1_set_cutoff(
 		bw_lp1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -589,7 +594,7 @@ static inline void bw_lp1_set_cutoff(
 static inline void bw_lp1_set_prewarp_at_cutoff(
 		bw_lp1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_init);
 
@@ -602,7 +607,7 @@ static inline void bw_lp1_set_prewarp_at_cutoff(
 static inline void bw_lp1_set_prewarp_freq(
 		bw_lp1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_lp1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_lp1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -616,7 +621,7 @@ static inline void bw_lp1_set_prewarp_freq(
 
 static inline char bw_lp1_coeffs_is_valid(
 		const bw_lp1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_lp1_coeffs"))
@@ -664,13 +669,13 @@ static inline char bw_lp1_coeffs_is_valid(
 static inline char bw_lp1_state_is_valid(
 		const bw_lp1_coeffs * BW_RESTRICT coeffs,
 		const bw_lp1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_lp1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_ls1.h b/include/bw_ls1.h
index a0994b2..e4d2e58 100644
--- a/include/bw_ls1.h
+++ b/include/bw_ls1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_mm1 bw_one_pole }}}
  *  description {{{
  *    First-order low shelf filter (6 dB/oct) with gain asymptotically
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_ls1_reset_state_multi()</code> and updated C++
@@ -148,7 +153,7 @@ static inline void bw_ls1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_ls1_update_coeffs_ctrl()
  *  ```>>> */
@@ -301,8 +306,8 @@ static inline char bw_ls1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_ls1_state`.
@@ -363,7 +368,7 @@ struct bw_ls1_state {
 
 static inline void bw_ls1_init(
 		bw_ls1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_mm1_init(&coeffs->mm1_coeffs);
 	bw_mm1_set_prewarp_at_cutoff(&coeffs->mm1_coeffs, 0);
@@ -386,7 +391,7 @@ static inline void bw_ls1_init(
 static inline void bw_ls1_set_sample_rate(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -412,7 +417,7 @@ static inline void bw_ls1_update_mm1_params(
 
 static inline void bw_ls1_reset_coeffs(
 		bw_ls1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
@@ -433,10 +438,10 @@ static inline float bw_ls1_reset_state(
 		const bw_ls1_coeffs * BW_RESTRICT coeffs,
 		bw_ls1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float y = bw_mm1_reset_state(&coeffs->mm1_coeffs, &state->mm1_state, x_0);
@@ -459,18 +464,18 @@ static inline void bw_ls1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_ls1_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -479,12 +484,12 @@ static inline void bw_ls1_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_ls1_update_coeffs_ctrl(
 		bw_ls1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
@@ -498,7 +503,7 @@ static inline void bw_ls1_update_coeffs_ctrl(
 
 static inline void bw_ls1_update_coeffs_audio(
 		bw_ls1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
@@ -513,11 +518,11 @@ static inline float bw_ls1_process1(
 		const bw_ls1_coeffs * BW_RESTRICT coeffs,
 		bw_ls1_state * BW_RESTRICT        state,
 		float x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -537,15 +542,15 @@ static inline void bw_ls1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_ls1_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -566,18 +571,18 @@ static inline void bw_ls1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(coeffs->dc_gain)) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -598,7 +603,7 @@ static inline void bw_ls1_process_multi(
 static inline void bw_ls1_set_cutoff(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -616,7 +621,7 @@ static inline void bw_ls1_set_cutoff(
 static inline void bw_ls1_set_prewarp_at_cutoff(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 
@@ -629,7 +634,7 @@ static inline void bw_ls1_set_prewarp_at_cutoff(
 static inline void bw_ls1_set_prewarp_freq(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -644,7 +649,7 @@ static inline void bw_ls1_set_prewarp_freq(
 static inline void bw_ls1_set_dc_gain_lin(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -662,7 +667,7 @@ static inline void bw_ls1_set_dc_gain_lin(
 static inline void bw_ls1_set_dc_gain_dB(
 		bw_ls1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -676,7 +681,7 @@ static inline void bw_ls1_set_dc_gain_dB(
 
 static inline char bw_ls1_coeffs_is_valid(
 		const bw_ls1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ls1_coeffs"))
@@ -700,17 +705,17 @@ static inline char bw_ls1_coeffs_is_valid(
 static inline char bw_ls1_state_is_valid(
 		const bw_ls1_coeffs * BW_RESTRICT coeffs,
 		const bw_ls1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_ls1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_mm1_state_is_valid(coeffs ? &coeffs->mm1_coeffs : NULL, &state->mm1_state);
+	return bw_mm1_state_is_valid(coeffs ? &coeffs->mm1_coeffs : BW_NULL, &state->mm1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_ls2.h b/include/bw_ls2.h
index 4faa214..47ab313 100644
--- a/include/bw_ls2.h
+++ b/include/bw_ls2.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -30,6 +30,7 @@
  *    <ul>
  *      <li>Version <strong>1.0.1</strong>:
  *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
  *          <li>Fixed typos in documentation of
  *              <code>bw_ls2_set_cutoff()</code>,
  *              <code>bw_ls2_set_dc_gain_lin()</code>, and
@@ -158,7 +159,7 @@ static inline void bw_ls2_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_ls2_update_coeffs_ctrl()
  *  ```>>> */
@@ -326,8 +327,8 @@ static inline char bw_ls2_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_ls2_state`.
@@ -395,7 +396,7 @@ struct bw_ls2_state {
 
 static inline void bw_ls2_init(
 		bw_ls2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_mm2_init(&coeffs->mm2_coeffs);
 	bw_mm2_set_prewarp_at_cutoff(&coeffs->mm2_coeffs, 0);
@@ -416,7 +417,7 @@ static inline void bw_ls2_init(
 static inline void bw_ls2_set_sample_rate(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -448,7 +449,7 @@ static inline void bw_ls2_update_mm2_params(
 
 static inline void bw_ls2_reset_coeffs(
 		bw_ls2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
@@ -469,10 +470,10 @@ static inline float bw_ls2_reset_state(
 		const bw_ls2_coeffs * BW_RESTRICT coeffs,
 		bw_ls2_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float y = bw_mm2_reset_state(&coeffs->mm2_coeffs, &state->mm2_state, x_0);
@@ -495,18 +496,18 @@ static inline void bw_ls2_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_ls2_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -515,12 +516,12 @@ static inline void bw_ls2_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_ls2_update_coeffs_ctrl(
 		bw_ls2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
@@ -534,7 +535,7 @@ static inline void bw_ls2_update_coeffs_ctrl(
 
 static inline void bw_ls2_update_coeffs_audio(
 		bw_ls2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
@@ -549,11 +550,11 @@ static inline float bw_ls2_process1(
 		const bw_ls2_coeffs * BW_RESTRICT coeffs,
 		bw_ls2_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -573,15 +574,15 @@ static inline void bw_ls2_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_ls2_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -602,18 +603,18 @@ static inline void bw_ls2_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) >= 1e-6f && coeffs->cutoff * bw_rcpf(bw_sqrtf(bw_sqrtf(coeffs->dc_gain))) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -634,7 +635,7 @@ static inline void bw_ls2_process_multi(
 static inline void bw_ls2_set_cutoff(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -655,7 +656,7 @@ static inline void bw_ls2_set_cutoff(
 static inline void bw_ls2_set_Q(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -670,7 +671,7 @@ static inline void bw_ls2_set_Q(
 static inline void bw_ls2_set_prewarp_at_cutoff(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 
@@ -683,7 +684,7 @@ static inline void bw_ls2_set_prewarp_at_cutoff(
 static inline void bw_ls2_set_prewarp_freq(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -698,7 +699,7 @@ static inline void bw_ls2_set_prewarp_freq(
 static inline void bw_ls2_set_dc_gain_lin(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -719,7 +720,7 @@ static inline void bw_ls2_set_dc_gain_lin(
 static inline void bw_ls2_set_dc_gain_dB(
 		bw_ls2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ls2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ls2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -733,7 +734,7 @@ static inline void bw_ls2_set_dc_gain_dB(
 
 static inline char bw_ls2_coeffs_is_valid(
 		const bw_ls2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ls2_coeffs"))
@@ -766,17 +767,17 @@ static inline char bw_ls2_coeffs_is_valid(
 static inline char bw_ls2_state_is_valid(
 		const bw_ls2_coeffs * BW_RESTRICT coeffs,
 		const bw_ls2_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_ls2_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : NULL, &state->mm2_state);
+	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : BW_NULL, &state->mm2_state);
 }
 
 #undef BW_LS2_PARAM_CUTOFF
diff --git a/include/bw_math.h b/include/bw_math.h
index 0f2b0e9..8280a21 100644
--- a/include/bw_math.h
+++ b/include/bw_math.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2021-2023 Orastron Srl unipersonale
+ * Copyright (C) 2021-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    A collection of mathematical routines that strive to be better suited to
@@ -44,6 +44,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Renamed <code>bw_min0xf()</code> as <code>bw_min0f()</code> and
@@ -756,8 +761,8 @@ static inline void bw_intfracf(
 		float * BW_RESTRICT i,
 		float * BW_RESTRICT f) {
 	BW_ASSERT(bw_is_finite(x));
-	BW_ASSERT(i != NULL);
-	BW_ASSERT(f != NULL);
+	BW_ASSERT(i != BW_NULL);
+	BW_ASSERT(f != BW_NULL);
 	BW_ASSERT(i != f);
 	*i = bw_floorf(x);
 	*f = x - *i;
diff --git a/include/bw_mm1.h b/include/bw_mm1.h
index 93c3933..df21826 100644
--- a/include/bw_mm1.h
+++ b/include/bw_mm1.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order multimode filter.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_mm1_reset_state_multi()</code> and updated C++
@@ -144,7 +149,7 @@ static inline void bw_mm1_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_mm1_update_coeffs_ctrl()
  *  ```>>> */
@@ -281,8 +286,8 @@ static inline char bw_mm1_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_mm1_state`.
@@ -338,7 +343,7 @@ struct bw_mm1_state {
 
 static inline void bw_mm1_init(
 		bw_mm1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_lp1_init(&coeffs->lp1_coeffs);
 	bw_gain_init(&coeffs->gain_x_coeffs);
@@ -360,7 +365,7 @@ static inline void bw_mm1_init(
 static inline void bw_mm1_set_sample_rate(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -378,7 +383,7 @@ static inline void bw_mm1_set_sample_rate(
 
 static inline void bw_mm1_reset_coeffs(
 		bw_mm1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_set_sample_rate);
 
@@ -398,10 +403,10 @@ static inline float bw_mm1_reset_state(
 		const bw_mm1_coeffs * BW_RESTRICT coeffs,
 		bw_mm1_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float lp = bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, x_0);
@@ -425,18 +430,18 @@ static inline void bw_mm1_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_mm1_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -445,12 +450,12 @@ static inline void bw_mm1_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_mm1_update_coeffs_ctrl(
 		bw_mm1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
 
@@ -464,7 +469,7 @@ static inline void bw_mm1_update_coeffs_ctrl(
 
 static inline void bw_mm1_update_coeffs_audio(
 		bw_mm1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
 
@@ -480,10 +485,10 @@ static inline float bw_mm1_process1(
 		const bw_mm1_coeffs * BW_RESTRICT coeffs,
 		bw_mm1_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -506,14 +511,14 @@ static inline void bw_mm1_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_mm1_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -534,17 +539,17 @@ static inline void bw_mm1_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -565,7 +570,7 @@ static inline void bw_mm1_process_multi(
 static inline void bw_mm1_set_cutoff(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -580,7 +585,7 @@ static inline void bw_mm1_set_cutoff(
 static inline void bw_mm1_set_prewarp_at_cutoff(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 
@@ -593,7 +598,7 @@ static inline void bw_mm1_set_prewarp_at_cutoff(
 static inline void bw_mm1_set_prewarp_freq(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -608,7 +613,7 @@ static inline void bw_mm1_set_prewarp_freq(
 static inline void bw_mm1_set_coeff_x(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -622,7 +627,7 @@ static inline void bw_mm1_set_coeff_x(
 static inline void bw_mm1_set_coeff_lp(
 		bw_mm1_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm1_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm1_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -635,7 +640,7 @@ static inline void bw_mm1_set_coeff_lp(
 
 static inline char bw_mm1_coeffs_is_valid(
 		const bw_mm1_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_mm1_coeffs"))
@@ -650,17 +655,17 @@ static inline char bw_mm1_coeffs_is_valid(
 static inline char bw_mm1_state_is_valid(
 		const bw_mm1_coeffs * BW_RESTRICT coeffs,
 		const bw_mm1_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_mm1_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : NULL, &state->lp1_state);
+	return bw_lp1_state_is_valid(coeffs ? &coeffs->lp1_coeffs : BW_NULL, &state->lp1_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_mm2.h b/include/bw_mm2.h
index 978c27b..482121e 100644
--- a/include/bw_mm2.h
+++ b/include/bw_mm2.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order multimode filter.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_mm2_reset_state_multi()</code> and updated C++
@@ -144,7 +149,7 @@ static inline void bw_mm2_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_mm2_update_coeffs_ctrl()
  *  ```>>> */
@@ -318,8 +323,8 @@ static inline char bw_mm2_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_mm2_state`.
@@ -377,7 +382,7 @@ struct bw_mm2_state {
 
 static inline void bw_mm2_init(
 		bw_mm2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->svf_coeffs);
 	bw_gain_init(&coeffs->gain_x_coeffs);
@@ -405,7 +410,7 @@ static inline void bw_mm2_init(
 static inline void bw_mm2_set_sample_rate(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -425,7 +430,7 @@ static inline void bw_mm2_set_sample_rate(
 
 static inline void bw_mm2_reset_coeffs(
 		bw_mm2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_set_sample_rate);
 
@@ -447,10 +452,10 @@ static inline float bw_mm2_reset_state(
 		const bw_mm2_coeffs * BW_RESTRICT coeffs,
 		bw_mm2_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float lp, bp, hp;
@@ -479,18 +484,18 @@ static inline void bw_mm2_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_mm2_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -499,12 +504,12 @@ static inline void bw_mm2_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_mm2_update_coeffs_ctrl(
 		bw_mm2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
 
@@ -520,7 +525,7 @@ static inline void bw_mm2_update_coeffs_ctrl(
 
 static inline void bw_mm2_update_coeffs_audio(
 		bw_mm2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
 
@@ -538,10 +543,10 @@ static inline float bw_mm2_process1(
 		const bw_mm2_coeffs * BW_RESTRICT coeffs,
 		bw_mm2_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -567,14 +572,14 @@ static inline void bw_mm2_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_mm2_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -595,17 +600,17 @@ static inline void bw_mm2_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -626,7 +631,7 @@ static inline void bw_mm2_process_multi(
 static inline void bw_mm2_set_cutoff(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -641,7 +646,7 @@ static inline void bw_mm2_set_cutoff(
 static inline void bw_mm2_set_Q(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -656,7 +661,7 @@ static inline void bw_mm2_set_Q(
 static inline void bw_mm2_set_prewarp_at_cutoff(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 
@@ -669,7 +674,7 @@ static inline void bw_mm2_set_prewarp_at_cutoff(
 static inline void bw_mm2_set_prewarp_freq(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -684,7 +689,7 @@ static inline void bw_mm2_set_prewarp_freq(
 static inline void bw_mm2_set_coeff_x(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -698,7 +703,7 @@ static inline void bw_mm2_set_coeff_x(
 static inline void bw_mm2_set_coeff_lp(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -712,7 +717,7 @@ static inline void bw_mm2_set_coeff_lp(
 static inline void bw_mm2_set_coeff_bp(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -726,7 +731,7 @@ static inline void bw_mm2_set_coeff_bp(
 static inline void bw_mm2_set_coeff_hp(
 		bw_mm2_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_mm2_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_mm2_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -739,7 +744,7 @@ static inline void bw_mm2_set_coeff_hp(
 
 static inline char bw_mm2_coeffs_is_valid(
 		const bw_mm2_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_mm2_coeffs"))
@@ -758,17 +763,17 @@ static inline char bw_mm2_coeffs_is_valid(
 static inline char bw_mm2_state_is_valid(
 		const bw_mm2_coeffs * BW_RESTRICT coeffs,
 		const bw_mm2_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_mm2_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : NULL, &state->svf_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : BW_NULL, &state->svf_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_noise_gate.h b/include/bw_noise_gate.h
index 4765830..321505e 100644
--- a/include/bw_noise_gate.h
+++ b/include/bw_noise_gate.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_env_follow bw_math bw_one_pole }}}
  *  description {{{
  *    Noise gate with independent sidechain input.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input values to
@@ -146,7 +151,7 @@ static inline void bw_noise_gate_reset_state_multi(
  *    array and sidechain input value in the `x_sc_0` array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_noise_gate_update_coeffs_ctrl()
  *  ```>>> */
@@ -291,8 +296,8 @@ static inline char bw_noise_gate_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_noise_gate_state`.
@@ -358,7 +363,7 @@ struct bw_noise_gate_state {
 
 static inline void bw_noise_gate_init(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_env_follow_init(&coeffs->env_follow_coeffs);
 	bw_one_pole_init(&coeffs->smooth_coeffs);
@@ -378,7 +383,7 @@ static inline void bw_noise_gate_init(
 static inline void bw_noise_gate_set_sample_rate(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -405,7 +410,7 @@ static inline void bw_noise_gate_do_update_coeffs_audio(
 
 static inline void bw_noise_gate_reset_coeffs(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_set_sample_rate);
 
@@ -427,10 +432,10 @@ static inline float bw_noise_gate_reset_state(
 		bw_noise_gate_state * BW_RESTRICT        state,
 		float                                    x_0,
 		float                                    x_sc_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 	BW_ASSERT(bw_is_finite(x_sc_0));
 
@@ -456,19 +461,19 @@ static inline void bw_noise_gate_reset_state_multi(
 		const float *                                         x_sc_0,
 		float *                                               y_0,
 		size_t                                                n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
-	BW_ASSERT(x_sc_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
+	BW_ASSERT(x_sc_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_noise_gate_reset_state(coeffs, state[i], x_0[i], x_sc_0[i]);
 	else
@@ -478,12 +483,12 @@ static inline void bw_noise_gate_reset_state_multi(
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_has_only_finite(y_0, n_channels));
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_noise_gate_update_coeffs_ctrl(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
 
@@ -495,7 +500,7 @@ static inline void bw_noise_gate_update_coeffs_ctrl(
 
 static inline void bw_noise_gate_update_coeffs_audio(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
 
@@ -510,10 +515,10 @@ static inline float bw_noise_gate_process1(
 		bw_noise_gate_state * BW_RESTRICT        state,
 		float                                    x,
 		float                                    x_sc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 	BW_ASSERT(bw_is_finite(x_sc));
@@ -536,16 +541,16 @@ static inline void bw_noise_gate_process(
 		const float *                      x_sc,
 		float *                            y,
 		size_t                             n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(x_sc != NULL);
+	BW_ASSERT(x_sc != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_sc, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_noise_gate_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -566,18 +571,18 @@ static inline void bw_noise_gate_process_multi(
 		float * const *                                       y,
 		size_t                                                n_channels,
 		size_t                                                n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(x_sc != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(x_sc != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -598,7 +603,7 @@ static inline void bw_noise_gate_process_multi(
 static inline void bw_noise_gate_set_thresh_lin(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -613,7 +618,7 @@ static inline void bw_noise_gate_set_thresh_lin(
 static inline void bw_noise_gate_set_thresh_dBFS(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -628,7 +633,7 @@ static inline void bw_noise_gate_set_thresh_dBFS(
 static inline void bw_noise_gate_set_ratio(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -643,7 +648,7 @@ static inline void bw_noise_gate_set_ratio(
 static inline void bw_noise_gate_set_attack_tau(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -658,7 +663,7 @@ static inline void bw_noise_gate_set_attack_tau(
 static inline void bw_noise_gate_set_release_tau(
 		bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		float                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gate_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gate_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -672,7 +677,7 @@ static inline void bw_noise_gate_set_release_tau(
 
 static inline char bw_noise_gate_coeffs_is_valid(
 		const bw_noise_gate_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_noise_gate_coeffs"))
@@ -709,17 +714,17 @@ static inline char bw_noise_gate_coeffs_is_valid(
 static inline char bw_noise_gate_state_is_valid(
 		const bw_noise_gate_coeffs * BW_RESTRICT coeffs,
 		const bw_noise_gate_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_noise_gate_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : NULL, &state->env_follow_state);
+	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : BW_NULL, &state->env_follow_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_noise_gen.h b/include/bw_noise_gen.h
index 2319c9f..b0a892b 100644
--- a/include/bw_noise_gen.h
+++ b/include/bw_noise_gen.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_rand }}}
  *  description {{{
  *    Generator of white noise with uniform distribution.
@@ -31,6 +31,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_noise_gen_reset_coeffs()</code>,
@@ -245,8 +250,8 @@ struct bw_noise_gen_coeffs {
 static inline void bw_noise_gen_init(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs,
 		uint64_t * BW_RESTRICT            state) {
-	BW_ASSERT(coeffs != NULL);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
+	BW_ASSERT(state != BW_NULL);
 
 	coeffs->rand_state = state;
 	coeffs->sample_rate_scaling = 0;
@@ -262,7 +267,7 @@ static inline void bw_noise_gen_init(
 static inline void bw_noise_gen_set_sample_rate(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -278,7 +283,7 @@ static inline void bw_noise_gen_set_sample_rate(
 
 static inline void bw_noise_gen_reset_coeffs(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_set_sample_rate);
 
@@ -293,7 +298,7 @@ static inline void bw_noise_gen_reset_coeffs(
 
 static inline void bw_noise_gen_update_coeffs_ctrl(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
 
@@ -302,7 +307,7 @@ static inline void bw_noise_gen_update_coeffs_ctrl(
 
 static inline void bw_noise_gen_update_coeffs_audio(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
 
@@ -311,7 +316,7 @@ static inline void bw_noise_gen_update_coeffs_audio(
 
 static inline float bw_noise_gen_process1(
 		const bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
 
@@ -326,7 +331,7 @@ static inline float bw_noise_gen_process1(
 
 static inline float bw_noise_gen_process1_scaling(
 		const bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
 
@@ -343,10 +348,10 @@ static inline void bw_noise_gen_process(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs,
 		float * BW_RESTRICT               y,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->sample_rate_scaling)
 		for (size_t i = 0; i < n_samples; i++)
@@ -365,10 +370,10 @@ static inline void bw_noise_gen_process_multi(
 		float * BW_RESTRICT const * BW_RESTRICT y,
 		size_t                                  n_channels,
 		size_t                                  n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -385,7 +390,7 @@ static inline void bw_noise_gen_process_multi(
 static inline void bw_noise_gen_set_sample_rate_scaling(
 		bw_noise_gen_coeffs * BW_RESTRICT coeffs,
 		char                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_init);
 
@@ -397,7 +402,7 @@ static inline void bw_noise_gen_set_sample_rate_scaling(
 
 static inline float bw_noise_gen_get_scaling_k(
 		const bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_noise_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_noise_gen_coeffs_state_set_sample_rate);
 
@@ -406,7 +411,7 @@ static inline float bw_noise_gen_get_scaling_k(
 
 static inline char bw_noise_gen_coeffs_is_valid(
 		const bw_noise_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_noise_gen_coeffs"))
@@ -415,7 +420,7 @@ static inline char bw_noise_gen_coeffs_is_valid(
 		return 0;
 #endif
 
-	if (coeffs->rand_state == NULL)
+	if (coeffs->rand_state == BW_NULL)
 		return 0;
 
 #ifdef BW_DEBUG_DEEP
diff --git a/include/bw_notch.h b/include/bw_notch.h
index b02ae45..63c50a3 100644
--- a/include/bw_notch.h
+++ b/include/bw_notch.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order notch filter with unitary gain at DC and asymptotically as
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_notch_reset_state_multi()</code> and updated C++
@@ -146,7 +151,7 @@ static inline void bw_notch_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_notch_update_coeffs_ctrl()
  *  ```>>> */
@@ -272,8 +277,8 @@ static inline char bw_notch_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_notch_state`.
@@ -326,7 +331,7 @@ struct bw_notch_state {
 
 static inline void bw_notch_init(
 		bw_notch_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->svf_coeffs);
 
@@ -342,7 +347,7 @@ static inline void bw_notch_init(
 static inline void bw_notch_set_sample_rate(
 		bw_notch_coeffs * BW_RESTRICT coeffs,
 		float                         sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -358,7 +363,7 @@ static inline void bw_notch_set_sample_rate(
 
 static inline void bw_notch_reset_coeffs(
 		bw_notch_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_set_sample_rate);
 
@@ -376,10 +381,10 @@ static inline float bw_notch_reset_state(
 		const bw_notch_coeffs * BW_RESTRICT coeffs,
 		bw_notch_state * BW_RESTRICT        state,
 		float                               x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float lp, bp, hp;
@@ -404,18 +409,18 @@ static inline void bw_notch_reset_state_multi(
 		const float *                                    x_0,
 		float *                                          y_0,
 		size_t                                           n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_notch_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -424,12 +429,12 @@ static inline void bw_notch_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_notch_update_coeffs_ctrl(
 		bw_notch_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
 
@@ -441,7 +446,7 @@ static inline void bw_notch_update_coeffs_ctrl(
 
 static inline void bw_notch_update_coeffs_audio(
 		bw_notch_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
 
@@ -455,10 +460,10 @@ static inline float bw_notch_process1(
 		const bw_notch_coeffs * BW_RESTRICT coeffs,
 		bw_notch_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -480,14 +485,14 @@ static inline void bw_notch_process(
 		const float *                 x,
 		float *                       y,
 		size_t                        n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_notch_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -508,17 +513,17 @@ static inline void bw_notch_process_multi(
 		float * const *                                  y,
 		size_t                                           n_channels,
 		size_t                                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -539,7 +544,7 @@ static inline void bw_notch_process_multi(
 static inline void bw_notch_set_cutoff(
 		bw_notch_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -554,7 +559,7 @@ static inline void bw_notch_set_cutoff(
 static inline void bw_notch_set_Q(
 		bw_notch_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -569,7 +574,7 @@ static inline void bw_notch_set_Q(
 static inline void bw_notch_set_prewarp_at_cutoff(
 		bw_notch_coeffs * BW_RESTRICT coeffs,
 		char                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_init);
 
@@ -582,7 +587,7 @@ static inline void bw_notch_set_prewarp_at_cutoff(
 static inline void bw_notch_set_prewarp_freq(
 		bw_notch_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_notch_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_notch_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -596,7 +601,7 @@ static inline void bw_notch_set_prewarp_freq(
 
 static inline char bw_notch_coeffs_is_valid(
 		const bw_notch_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_notch_coeffs"))
@@ -611,17 +616,17 @@ static inline char bw_notch_coeffs_is_valid(
 static inline char bw_notch_state_is_valid(
 		const bw_notch_coeffs * BW_RESTRICT coeffs,
 		const bw_notch_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_notch_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : NULL, &state->svf_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : BW_NULL, &state->svf_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_note_queue.h b/include/bw_note_queue.h
index 76758b9..c402f38 100644
--- a/include/bw_note_queue.h
+++ b/include/bw_note_queue.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Simple data structure that helps keeping track of note on/off events and
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Removed redundant <code>status</code> member from
@@ -172,7 +177,7 @@ extern "C" {
 
 static inline void bw_note_queue_reset(
 		bw_note_queue * BW_RESTRICT queue) {
-	BW_ASSERT(queue != NULL);
+	BW_ASSERT(queue != BW_NULL);
 	for (int i = 0; i < 128; i++) {
 		queue->status[i].pressed = 0;
 		queue->status[i].velocity = 0.f;
@@ -184,7 +189,7 @@ static inline void bw_note_queue_reset(
 
 static inline void bw_note_queue_clear(
 		bw_note_queue * BW_RESTRICT queue) {
-	BW_ASSERT(queue != NULL);
+	BW_ASSERT(queue != BW_NULL);
 	BW_ASSERT_DEEP(bw_note_queue_is_valid(queue));
 	queue->n_events = 0;
 }
@@ -195,7 +200,7 @@ static inline void bw_note_queue_add(
 		char                        pressed,
 		float                       velocity,
 		char                        force_went_off) {
-	BW_ASSERT(queue != NULL);
+	BW_ASSERT(queue != BW_NULL);
 	BW_ASSERT_DEEP(bw_note_queue_is_valid(queue));
 	BW_ASSERT(note < 128);
 	BW_ASSERT(bw_is_finite(velocity) && velocity <= 1.f);
@@ -227,7 +232,7 @@ static inline void bw_note_queue_add(
 
 static inline char bw_note_queue_is_valid(
 		const bw_note_queue * BW_RESTRICT queue) {
-	BW_ASSERT(queue != NULL);
+	BW_ASSERT(queue != BW_NULL);
 
 	if (queue->n_events >= 128 || queue->n_pressed >= 128)
 		return 0;
diff --git a/include/bw_one_pole.h b/include/bw_one_pole.h
index c9d9ca4..59fbac9 100644
--- a/include/bw_one_pole.h
+++ b/include/bw_one_pole.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    One-pole (6 dB/oct) lowpass filter with unitary DC gain, separate attack
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_one_pole_reset_state_multi()</code> and updated
@@ -174,7 +179,7 @@ static inline void bw_one_pole_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the
- *    `y_0` array, if not `NULL`.
+ *    `y_0` array, if not `BW_NULL`.
  *
  *    #### bw_one_pole_update_coeffs_ctrl()
  *  ```>>> */
@@ -262,7 +267,7 @@ static inline void bw_one_pole_process(
  *    first `n_samples` of the output buffer `y`, while using and updating both
  *    `coeffs` and `state` (control and audio rate).
  *
- *    `y` may be `NULL`.
+ *    `y` may be `BW_NULL`.
  *
  *    #### bw_one_pole_process_multi()
  *  ```>>> */
@@ -279,7 +284,7 @@ static inline void bw_one_pole_process_multi(
  *    using and updating both the common `coeffs` and each of the `n_channels`
  *    `state`s (control and audio rate).
  *
- *    `y` or any element of `y` may be `NULL`.
+ *    `y` or any element of `y` may be `BW_NULL`.
  *
  *    #### bw_one_pole_set_cutoff()
  *  ```>>> */
@@ -438,8 +443,8 @@ static inline char bw_one_pole_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_one_pole_state`.
@@ -507,7 +512,7 @@ struct bw_one_pole_state {
 
 static inline void bw_one_pole_init(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->cutoff_up = INFINITY;
 	coeffs->cutoff_down = INFINITY;
@@ -526,7 +531,7 @@ static inline void bw_one_pole_init(
 static inline void bw_one_pole_set_sample_rate(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -557,7 +562,7 @@ static inline void bw_one_pole_do_update_coeffs_ctrl(
 
 static inline void bw_one_pole_reset_coeffs(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_set_sample_rate);
 
@@ -576,10 +581,10 @@ static inline float bw_one_pole_reset_state(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	(void)coeffs;
@@ -604,18 +609,18 @@ static inline void bw_one_pole_reset_state_multi(
 		const float *                                       x_0,
 		float *                                             y_0,
 		size_t                                              n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_one_pole_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -624,12 +629,12 @@ static inline void bw_one_pole_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_one_pole_update_coeffs_ctrl(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
 
@@ -641,7 +646,7 @@ static inline void bw_one_pole_update_coeffs_ctrl(
 
 static inline void bw_one_pole_update_coeffs_audio(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
 
@@ -652,10 +657,10 @@ static inline float bw_one_pole_process1(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -674,10 +679,10 @@ static inline float bw_one_pole_process1_sticky_abs(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -699,10 +704,10 @@ static inline float bw_one_pole_process1_sticky_rel(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -724,10 +729,10 @@ static inline float bw_one_pole_process1_asym(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -746,10 +751,10 @@ static inline float bw_one_pole_process1_asym_sticky_abs(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -771,10 +776,10 @@ static inline float bw_one_pole_process1_asym_sticky_rel(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -798,16 +803,16 @@ static inline void bw_one_pole_process(
 		const float *                    x,
 		float *                          y,
 		size_t                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
 
 	bw_one_pole_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
+	if (y != BW_NULL) {
 		if (coeffs->mA1u != coeffs->mA1d) {
 			if (coeffs->st2 != 0.f) {
 				if (coeffs->sticky_mode == bw_one_pole_sticky_mode_abs)
@@ -870,7 +875,7 @@ static inline void bw_one_pole_process(
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
 }
 
 static inline void bw_one_pole_process_multi(
@@ -880,30 +885,30 @@ static inline void bw_one_pole_process_multi(
 		float * const *                                     y,
 		size_t                                              n_channels,
 		size_t                                              n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
+				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 #endif
 
 	bw_one_pole_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
+	if (y != BW_NULL) {
 		if (coeffs->mA1u != coeffs->mA1d) {
 			if (coeffs->st2 != 0.f) {
 				if (coeffs->sticky_mode == bw_one_pole_sticky_mode_abs)
 					for (size_t j = 0; j < n_channels; j++)
-						if (y[j] != NULL)
+						if (y[j] != BW_NULL)
 							for (size_t i = 0; i < n_samples; i++)
 								y[j][i] = bw_one_pole_process1_asym_sticky_abs(coeffs, state[j], x[j][i]);
 						else
@@ -912,7 +917,7 @@ static inline void bw_one_pole_process_multi(
 
 				else
 					for (size_t j = 0; j < n_channels; j++)
-						if (y[j] != NULL)
+						if (y[j] != BW_NULL)
 							for (size_t i = 0; i < n_samples; i++)
 								y[j][i] = bw_one_pole_process1_asym_sticky_rel(coeffs, state[j], x[j][i]);
 						else
@@ -921,7 +926,7 @@ static inline void bw_one_pole_process_multi(
 			}
 			else {
 				for (size_t j = 0; j < n_channels; j++)
-					if (y[j] != NULL)
+					if (y[j] != BW_NULL)
 						for (size_t i = 0; i < n_samples; i++)
 							y[j][i] = bw_one_pole_process1_asym(coeffs, state[j], x[j][i]);
 					else
@@ -933,7 +938,7 @@ static inline void bw_one_pole_process_multi(
 			if (coeffs->st2 != 0.f) {
 				if (coeffs->sticky_mode == bw_one_pole_sticky_mode_abs)
 					for (size_t j = 0; j < n_channels; j++)
-						if (y[j] != NULL)
+						if (y[j] != BW_NULL)
 							for (size_t i = 0; i < n_samples; i++)
 								y[j][i] = bw_one_pole_process1_sticky_abs(coeffs, state[j], x[j][i]);
 						else
@@ -941,7 +946,7 @@ static inline void bw_one_pole_process_multi(
 								bw_one_pole_process1_sticky_abs(coeffs, state[j], x[j][i]);
 				else
 					for (size_t j = 0; j < n_channels; j++)
-						if (y[j] != NULL)
+						if (y[j] != BW_NULL)
 							for (size_t i = 0; i < n_samples; i++)
 								y[j][i] = bw_one_pole_process1_sticky_rel(coeffs, state[j], x[j][i]);
 						else
@@ -950,7 +955,7 @@ static inline void bw_one_pole_process_multi(
 			}
 			else {
 				for (size_t j = 0; j < n_channels; j++)
-					if (y[j] != NULL)
+					if (y[j] != BW_NULL)
 						for (size_t i = 0; i < n_samples; i++)
 							y[j][i] = bw_one_pole_process1(coeffs, state[j], x[j][i]);
 					else
@@ -1002,7 +1007,7 @@ static inline void bw_one_pole_process_multi(
 static inline void bw_one_pole_set_cutoff(
 		bw_one_pole_coeffs *BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1018,7 +1023,7 @@ static inline void bw_one_pole_set_cutoff(
 static inline void bw_one_pole_set_cutoff_up(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1039,7 +1044,7 @@ static inline void bw_one_pole_set_cutoff_up(
 static inline void bw_one_pole_set_cutoff_down(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1060,7 +1065,7 @@ static inline void bw_one_pole_set_cutoff_down(
 static inline void bw_one_pole_set_tau(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1076,7 +1081,7 @@ static inline void bw_one_pole_set_tau(
 static inline void bw_one_pole_set_tau_up(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1092,7 +1097,7 @@ static inline void bw_one_pole_set_tau_up(
 static inline void bw_one_pole_set_tau_down(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1108,7 +1113,7 @@ static inline void bw_one_pole_set_tau_down(
 static inline void bw_one_pole_set_sticky_thresh(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -1129,7 +1134,7 @@ static inline void bw_one_pole_set_sticky_thresh(
 static inline void bw_one_pole_set_sticky_mode(
 		bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		bw_one_pole_sticky_mode          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_one_pole_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_one_pole_coeffs_state_init);
 	BW_ASSERT(value == bw_one_pole_sticky_mode_abs || value == bw_one_pole_sticky_mode_rel);
@@ -1142,15 +1147,15 @@ static inline void bw_one_pole_set_sticky_mode(
 
 static inline float bw_one_pole_get_y_z1(
 		const bw_one_pole_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_one_pole_state_is_valid(BW_NULL, state));
 
 	return state->y_z1;
 }
 
 static inline char bw_one_pole_coeffs_is_valid(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_one_pole_coeffs"))
@@ -1190,13 +1195,13 @@ static inline char bw_one_pole_coeffs_is_valid(
 static inline char bw_one_pole_state_is_valid(
 		const bw_one_pole_coeffs * BW_RESTRICT coeffs,
 		const bw_one_pole_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_one_pole_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_osc_filt.h b/include/bw_osc_filt.h
index 542b467..00fe322 100644
--- a/include/bw_osc_filt.h
+++ b/include/bw_osc_filt.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Post-filter to decolorate oscillator waveshapers when antialiasing is on.
@@ -33,6 +33,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input value to
@@ -120,7 +125,7 @@ static inline void bw_osc_filt_reset_state_multi(
  *    corresponding initial input value in the `x_0` array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_osc_filt_process1()
  *  ```>>> */
@@ -194,7 +199,7 @@ struct bw_osc_filt_state {
 static inline float bw_osc_filt_reset_state(
 		bw_osc_filt_state * BW_RESTRICT state,
 		float                           x_0) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	state->z1 = 0.f;
@@ -214,28 +219,28 @@ static inline void bw_osc_filt_reset_state_multi(
 		const float *                                       x_0,
 		float *                                             y_0,
 		size_t                                              n_channels) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_osc_filt_reset_state(state[i], x_0[i]);
 	else
 		for (size_t i = 0; i < n_channels; i++)
 			bw_osc_filt_reset_state(state[i], x_0[i]);
 
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline float bw_osc_filt_process1(
 		bw_osc_filt_state * BW_RESTRICT state,
 		float                           x) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -253,11 +258,11 @@ static inline void bw_osc_filt_process(
 		const float *                   x,
 		float *                         y,
 		size_t                          n_samples) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	for (size_t i = 0; i < n_samples; i++)
 		y[i] = bw_osc_filt_process1(state, x[i]);
@@ -272,14 +277,14 @@ static inline void bw_osc_filt_process_multi(
 		float * const *                                     y,
 		size_t                                              n_channels,
 		size_t                                              n_samples) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -292,7 +297,7 @@ static inline void bw_osc_filt_process_multi(
 
 static inline char bw_osc_filt_state_is_valid(
 	const bw_osc_filt_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_osc_filt_state"))
diff --git a/include/bw_osc_pulse.h b/include/bw_osc_pulse.h
index edf9074..87cd154 100644
--- a/include/bw_osc_pulse.h
+++ b/include/bw_osc_pulse.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Pulse oscillator waveshaper with variable pulse width (actually, duty
@@ -37,6 +37,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li><code>bw_osc_pulse_process()</code> and
@@ -177,7 +182,7 @@ static inline void bw_osc_pulse_process(
  *    buffer `y`, while using and updating `coeffs` (control and audio rate).
  *
  *    If antialiasing is enabled, `x_inc` must contain phase increment
- *    values, otherwise it is ignored and can be `NULL`.
+ *    values, otherwise it is ignored and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -200,7 +205,7 @@ static inline void bw_osc_pulse_process_multi(
  *
  *    If antialiasing is enabled, each of the `n_channels` buffers pointed by
  *    `x_inc` must contain phase increment values, otherwise `x_inc` is ignored
- *    and can be `NULL`.
+ *    and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -284,7 +289,7 @@ struct bw_osc_pulse_coeffs {
 
 static inline void bw_osc_pulse_init(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -302,7 +307,7 @@ static inline void bw_osc_pulse_init(
 static inline void bw_osc_pulse_set_sample_rate(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -319,7 +324,7 @@ static inline void bw_osc_pulse_set_sample_rate(
 
 static inline void bw_osc_pulse_reset_coeffs(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_set_sample_rate);
 
@@ -334,7 +339,7 @@ static inline void bw_osc_pulse_reset_coeffs(
 
 static inline void bw_osc_pulse_update_coeffs_ctrl(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
 
@@ -343,7 +348,7 @@ static inline void bw_osc_pulse_update_coeffs_ctrl(
 
 static inline void bw_osc_pulse_update_coeffs_audio(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
 
@@ -356,7 +361,7 @@ static inline void bw_osc_pulse_update_coeffs_audio(
 static inline float bw_osc_pulse_process1(
 		const bw_osc_pulse_coeffs * BW_RESTRICT coeffs,
 		float                                   x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -384,7 +389,7 @@ static inline float bw_osc_pulse_process1_antialias(
 		const bw_osc_pulse_coeffs * BW_RESTRICT coeffs,
 		float                                   x,
 		float                                   x_inc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -425,14 +430,14 @@ static inline void bw_osc_pulse_process(
 		const float *                     x_inc,
 		float *                           y,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(coeffs->antialiasing ? x_inc != NULL : 1);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT_DEEP(coeffs->antialiasing ? bw_has_only_finite(x_inc, n_samples) : 1);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->antialiasing)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -457,11 +462,11 @@ static inline void bw_osc_pulse_process_multi(
 		float * const *                   y,
 		size_t                            n_channels,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -488,7 +493,7 @@ static inline void bw_osc_pulse_process_multi(
 static inline void bw_osc_pulse_set_antialiasing(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs,
 		char                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_init);
 
@@ -501,7 +506,7 @@ static inline void bw_osc_pulse_set_antialiasing(
 static inline void bw_osc_pulse_set_pulse_width(
 		bw_osc_pulse_coeffs * BW_RESTRICT coeffs,
 		float                             value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -515,7 +520,7 @@ static inline void bw_osc_pulse_set_pulse_width(
 
 static inline char bw_osc_pulse_coeffs_is_valid(
 		const bw_osc_pulse_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_osc_pulse_coeffs"))
diff --git a/include/bw_osc_saw.h b/include/bw_osc_saw.h
index 18f9199..944f00c 100644
--- a/include/bw_osc_saw.h
+++ b/include/bw_osc_saw.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sawtooth oscillator waveshaper with PolyBLEP antialiasing.
@@ -36,6 +36,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_osc_saw_set_sample_rate()</code>,
@@ -180,7 +185,7 @@ static inline void bw_osc_saw_process(
  *    buffer `y`, while using `coeffs`.
  *
  *    If antialiasing is enabled, `x_inc` must contain phase increment values,
- *    otherwise it is ignored and can be `NULL`.
+ *    otherwise it is ignored and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -202,7 +207,7 @@ static inline void bw_osc_saw_process_multi(
  *
  *    If antialiasing is enabled, each of the `n_channels` buffers pointed by
  *    `x_inc` must contain phase increment values, otherwise `x_inc` is ignored
- *    and can be `NULL`.
+ *    and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -268,7 +273,7 @@ struct bw_osc_saw_coeffs {
 
 static inline void bw_osc_saw_init(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->antialiasing = 0;
 
@@ -283,7 +288,7 @@ static inline void bw_osc_saw_init(
 static inline void bw_osc_saw_set_sample_rate(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs,
 		float                           sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -300,7 +305,7 @@ static inline void bw_osc_saw_set_sample_rate(
 
 static inline void bw_osc_saw_reset_coeffs(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_set_sample_rate);
 
@@ -315,7 +320,7 @@ static inline void bw_osc_saw_reset_coeffs(
 
 static inline void bw_osc_saw_update_coeffs_ctrl(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
 
@@ -324,7 +329,7 @@ static inline void bw_osc_saw_update_coeffs_ctrl(
 
 static inline void bw_osc_saw_update_coeffs_audio(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
 
@@ -334,7 +339,7 @@ static inline void bw_osc_saw_update_coeffs_audio(
 static inline float bw_osc_saw_process1(
 		const bw_osc_saw_coeffs * BW_RESTRICT coeffs,
 		float                                 x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -362,7 +367,7 @@ static inline float bw_osc_saw_process1_antialias(
 		const bw_osc_saw_coeffs * BW_RESTRICT coeffs,
 		float                                 x,
 		float                                 x_inc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -396,14 +401,14 @@ static inline void bw_osc_saw_process(
 		const float *                   x_inc,
 		float *                         y,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(coeffs->antialiasing ? x_inc != NULL : 1);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT_DEEP(coeffs->antialiasing ? bw_has_only_finite(x_inc, n_samples) : 1);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->antialiasing)
 		for (size_t i = 0; i < n_samples; i++)
@@ -424,23 +429,23 @@ static inline void bw_osc_saw_process_multi(
 		float * const *                 y,
 		size_t                          n_channels,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(y[i] != y[j]);
 #endif
 
-	if (x_inc != NULL)
+	if (x_inc != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			bw_osc_saw_process(coeffs, x[i], x_inc[i], y[i], n_samples);
 	else
 		for (size_t i = 0; i < n_channels; i++)
-			bw_osc_saw_process(coeffs, x[i], NULL, y[i], n_samples);
+			bw_osc_saw_process(coeffs, x[i], BW_NULL, y[i], n_samples);
 
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
@@ -449,7 +454,7 @@ static inline void bw_osc_saw_process_multi(
 static inline void bw_osc_saw_set_antialiasing(
 		bw_osc_saw_coeffs * BW_RESTRICT coeffs,
 		char                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_init);
 
@@ -461,7 +466,7 @@ static inline void bw_osc_saw_set_antialiasing(
 
 static inline char bw_osc_saw_coeffs_is_valid(
 		const bw_osc_saw_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_osc_saw_coeffs"))
diff --git a/include/bw_osc_sin.h b/include/bw_osc_sin.h
index c5728b5..9ccceaa 100644
--- a/include/bw_osc_sin.h
+++ b/include/bw_osc_sin.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sinusoidal oscillator waveshaper.
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li><code>bw_osc_sin_process()</code> and
@@ -149,9 +154,9 @@ static inline void bw_osc_sin_process(
 		const float * x,
 		float *       y,
 		size_t        n_samples) {
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	for (size_t i = 0; i < n_samples; i++)
 		y[i] = bw_osc_sin_process1(x[i]);
@@ -164,8 +169,8 @@ static inline void bw_osc_sin_process_multi(
 		float * const *       y,
 		size_t                n_channels,
 		size_t                n_samples) {
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
diff --git a/include/bw_osc_tri.h b/include/bw_osc_tri.h
index 3b414e5..9d547f1 100644
--- a/include/bw_osc_tri.h
+++ b/include/bw_osc_tri.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Triangle oscillator waveshaper with variable slope (increasing time over
@@ -37,6 +37,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li><code>bw_osc_tri_process()</code> and
@@ -179,7 +184,7 @@ static inline void bw_osc_tri_process(
  *    buffer `y`, while using and updating `coeffs`.
  *
  *    If antialiasing is enabled, `x_inc` must contain phase increment values,
- *    otherwise it is ignored and can be `NULL`.
+ *    otherwise it is ignored and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -201,7 +206,7 @@ static inline void bw_osc_tri_process_multi(
  *    common `coeffs` (control and audio rate).
  *
  *    If antialiasing is enabled, `x_inc` must contain `n_channels` buffers of
- *    phase increment values, otherwise it is ignored and can be `NULL`.
+ *    phase increment values, otherwise it is ignored and can be `BW_NULL`.
  *
  *    All samples in `x` must be in [`0.f`, `1.f`).
  *
@@ -285,7 +290,7 @@ struct bw_osc_tri_coeffs {
 
 static inline void bw_osc_tri_init(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -303,7 +308,7 @@ static inline void bw_osc_tri_init(
 static inline void bw_osc_tri_set_sample_rate(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs,
 		float                           sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -320,7 +325,7 @@ static inline void bw_osc_tri_set_sample_rate(
 
 static inline void bw_osc_tri_reset_coeffs(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_set_sample_rate);
 
@@ -335,7 +340,7 @@ static inline void bw_osc_tri_reset_coeffs(
 
 static inline void bw_osc_tri_update_coeffs_ctrl(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
 
@@ -344,7 +349,7 @@ static inline void bw_osc_tri_update_coeffs_ctrl(
 
 static inline void bw_osc_tri_update_coeffs_audio(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
 
@@ -357,7 +362,7 @@ static inline void bw_osc_tri_update_coeffs_audio(
 static inline float bw_osc_tri_process1(
 		const bw_osc_tri_coeffs * BW_RESTRICT coeffs,
 		float                                 x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -386,7 +391,7 @@ static inline float bw_osc_tri_process1_antialias(
 		const bw_osc_tri_coeffs * BW_RESTRICT coeffs,
 		float                                 x,
 		float                                 x_inc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
@@ -432,14 +437,14 @@ static inline void bw_osc_tri_process(
 		const float *                   x_inc,
 		float *                         y,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(coeffs->antialiasing ? x_inc != NULL : 1);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT_DEEP(coeffs->antialiasing ? bw_has_only_finite(x_inc, n_samples) : 1);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->antialiasing)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -464,11 +469,11 @@ static inline void bw_osc_tri_process_multi(
 		float * const *                 y,
 		size_t                          n_channels,
 		size_t                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -495,7 +500,7 @@ static inline void bw_osc_tri_process_multi(
 static inline void bw_osc_tri_set_antialiasing(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs,
 		char                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_init);
 
@@ -508,7 +513,7 @@ static inline void bw_osc_tri_set_antialiasing(
 static inline void bw_osc_tri_set_slope(
 		bw_osc_tri_coeffs * BW_RESTRICT coeffs,
 		float                           value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -522,7 +527,7 @@ static inline void bw_osc_tri_set_slope(
 
 static inline char bw_osc_tri_coeffs_is_valid(
 		const bw_osc_tri_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_osc_tri_coeffs"))
diff --git a/include/bw_pan.h b/include/bw_pan.h
index 4aaf4d8..81bd33d 100644
--- a/include/bw_pan.h
+++ b/include/bw_pan.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole }}}
  *  description {{{
  *    Stereo panner with -3 dB center pan law.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Now using parabolic curves instead of trigonometric ones.</li>
@@ -225,7 +230,7 @@ struct bw_pan_coeffs {
 
 static inline void bw_pan_init(
 		bw_pan_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_gain_init(&coeffs->l_coeffs);
 	bw_gain_init(&coeffs->r_coeffs);
@@ -242,7 +247,7 @@ static inline void bw_pan_init(
 static inline void bw_pan_set_sample_rate(
 		bw_pan_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -270,7 +275,7 @@ static inline void bw_pan_do_update_coeffs(
 
 static inline void bw_pan_reset_coeffs(
 		bw_pan_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_set_sample_rate);
 
@@ -287,7 +292,7 @@ static inline void bw_pan_reset_coeffs(
 
 static inline void bw_pan_update_coeffs_ctrl(
 		bw_pan_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_reset_coeffs);
 
@@ -301,7 +306,7 @@ static inline void bw_pan_update_coeffs_ctrl(
 
 static inline void bw_pan_update_coeffs_audio(
 		bw_pan_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_reset_coeffs);
 
@@ -317,12 +322,12 @@ static inline void bw_pan_process1(
 		float                             x,
 		float * BW_RESTRICT               y_l,
 		float * BW_RESTRICT               y_r) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x));
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 
 	*y_l = bw_gain_process1(&coeffs->l_coeffs, x);
@@ -340,13 +345,13 @@ static inline void bw_pan_process(
 		float *                     y_l,
 		float *                     y_r,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 
 	bw_pan_update_coeffs_ctrl(coeffs);
@@ -368,12 +373,12 @@ static inline void bw_pan_process_multi(
 		float * const *             y_r,
 		size_t                      n_channels,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_reset_coeffs);
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
@@ -400,7 +405,7 @@ static inline void bw_pan_process_multi(
 static inline void bw_pan_set_pan(
 		bw_pan_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pan_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pan_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -414,7 +419,7 @@ static inline void bw_pan_set_pan(
 
 static inline char bw_pan_coeffs_is_valid(
 		const bw_pan_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_pan_coeffs"))
diff --git a/include/bw_peak.h b/include/bw_peak.h
index c77c097..8d7fd4c 100644
--- a/include/bw_peak.h
+++ b/include/bw_peak.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_mm2 bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order peak filter with unitary gain at DC and asymptotically
@@ -35,6 +35,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_peak_reset_state_multi()</code> and updated C++
@@ -157,7 +162,7 @@ static inline void bw_peak_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_peak_update_coeffs_ctrl()
  *  ```>>> */
@@ -352,8 +357,8 @@ static inline char bw_peak_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_peak_state`.
@@ -421,7 +426,7 @@ struct bw_peak_state {
 
 static inline void bw_peak_init(
 		bw_peak_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_mm2_init(&coeffs->mm2_coeffs);
 	coeffs->Q = 0.5f;
@@ -441,7 +446,7 @@ static inline void bw_peak_init(
 static inline void bw_peak_set_sample_rate(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -479,7 +484,7 @@ static inline void bw_peak_update_mm2_params(
 
 static inline void bw_peak_reset_coeffs(
 		bw_peak_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->use_bandwidth
@@ -503,10 +508,10 @@ static inline float bw_peak_reset_state(
 		const bw_peak_coeffs * BW_RESTRICT coeffs,
 		bw_peak_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float y = bw_mm2_reset_state(&coeffs->mm2_coeffs, &state->mm2_state, x_0);
@@ -529,18 +534,18 @@ static inline void bw_peak_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_peak_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -549,12 +554,12 @@ static inline void bw_peak_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_peak_update_coeffs_ctrl(
 		bw_peak_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->use_bandwidth
@@ -571,7 +576,7 @@ static inline void bw_peak_update_coeffs_ctrl(
 
 static inline void bw_peak_update_coeffs_audio(
 		bw_peak_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->use_bandwidth
@@ -589,14 +594,14 @@ static inline float bw_peak_process1(
 		const bw_peak_coeffs * BW_RESTRICT coeffs,
 		bw_peak_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->use_bandwidth
 		? bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) >= 1e-6f
 			&& bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) <= 1e6f
 		: 1);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -616,18 +621,18 @@ static inline void bw_peak_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->use_bandwidth
 		? bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) >= 1e-6f
 			&& bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) <= 1e6f
 		: 1);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_peak_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -648,7 +653,7 @@ static inline void bw_peak_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_reset_coeffs);
@@ -656,14 +661,14 @@ static inline void bw_peak_process_multi(
 		? bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) >= 1e-6f
 			&& bw_sqrtf(bw_pow2f(coeffs->bandwidth) * coeffs->peak_gain) * bw_rcpf(bw_pow2f(coeffs->bandwidth) - 1.f) <= 1e6f
 		: 1);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -684,7 +689,7 @@ static inline void bw_peak_process_multi(
 static inline void bw_peak_set_cutoff(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -699,7 +704,7 @@ static inline void bw_peak_set_cutoff(
 static inline void bw_peak_set_Q(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -720,7 +725,7 @@ static inline void bw_peak_set_Q(
 static inline void bw_peak_set_prewarp_at_cutoff(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 
@@ -733,7 +738,7 @@ static inline void bw_peak_set_prewarp_at_cutoff(
 static inline void bw_peak_set_prewarp_freq(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -748,7 +753,7 @@ static inline void bw_peak_set_prewarp_freq(
 static inline void bw_peak_set_peak_gain_lin(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -769,7 +774,7 @@ static inline void bw_peak_set_peak_gain_lin(
 static inline void bw_peak_set_peak_gain_dB(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -784,7 +789,7 @@ static inline void bw_peak_set_peak_gain_dB(
 static inline void bw_peak_set_bandwidth(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -805,7 +810,7 @@ static inline void bw_peak_set_bandwidth(
 static inline void bw_peak_set_use_bandwidth(
 		bw_peak_coeffs * BW_RESTRICT coeffs,
 		char                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_peak_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_peak_coeffs_state_init);
 
@@ -823,7 +828,7 @@ static inline void bw_peak_set_use_bandwidth(
 
 static inline char bw_peak_coeffs_is_valid(
 		const bw_peak_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_peak_coeffs"))
@@ -852,17 +857,17 @@ static inline char bw_peak_coeffs_is_valid(
 static inline char bw_peak_state_is_valid(
 		const bw_peak_coeffs * BW_RESTRICT coeffs,
 		const bw_peak_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_peak_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : NULL, &state->mm2_state);
+	return bw_mm2_state_is_valid(coeffs ? &coeffs->mm2_coeffs : BW_NULL, &state->mm2_state);
 }
 
 #undef BW_PEAK_PARAM_Q
diff --git a/include/bw_phase_gen.h b/include/bw_phase_gen.h
index 4f5d66d..2a258dd 100644
--- a/include/bw_phase_gen.h
+++ b/include/bw_phase_gen.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -31,7 +31,8 @@
  *    <ul>
  *      <li>Version <strong>1.0.1</strong>:
  *        <ul>
- *          <li>Fixed rouding bug when frequency is tiny and negative.</li>
+ *          <li>Fixed rounding bug when frequency is tiny and negative.</li>
+ *          <li>Now using <code>BW_NULL</code>.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>1.0.0</strong>:
@@ -169,7 +170,7 @@ static inline void bw_phase_gen_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output and phase increment values are put into
- *    the `y_0` and `y_inc_0` arrays, respectively, if they are not `NULL`.
+ *    the `y_0` and `y_inc_0` arrays, respectively, if they are not `BW_NULL`.
  *
  *    #### bw_phase_gen_update_coeffs_ctrl()
  *  ```>>> */
@@ -222,10 +223,10 @@ static inline void bw_phase_gen_process(
  *    Generates and fills the first `n_samples` of the output buffer `y`, while
  *    using and updating both `coeffs` and `state` (control and audio rate).
  *
- *    If `x_mod` is not `NULL`, it is used as a source of exponential frequency
- *    modulation (scale `1.f`/octave).
+ *    If `x_mod` is not `BW_NULL`, it is used as a source of exponential
+ *    frequency modulation (scale `1.f`/octave).
  *
- *    If `y_inc` is not `NULL`, it is filled with phase increment values.
+ *    If `y_inc` is not `BW_NULL`, it is filled with phase increment values.
  *
  *    #### bw_phase_gen_process_multi()
  *  ```>>> */
@@ -242,12 +243,12 @@ static inline void bw_phase_gen_process_multi(
  *    buffers `y`, while using and updating both the common `coeffs` and each of
  *    the `n_channels` `state`s (control and audio rate).
  *
- *    If `x_mod` and the channel-specific element are not `NULL`, this is used
- *    as a source of exponential frequency modulation (scale `1.f`/octave) for
- *    that channel.
+ *    If `x_mod` and the channel-specific element are not `BW_NULL`, this is
+ *    used as a source of exponential frequency modulation (scale `1.f`/octave)
+ *    for that channel.
  *
- *    If `y_inc` and the channel-specific element are not `NULL`, this is filled
- *    with phase increment values for that channel.
+ *    If `y_inc` and the channel-specific element are not `BW_NULL`, this is
+ *    filled with phase increment values for that channel.
  *
  *    #### bw_phase_gen_set_frequency()
  *  ```>>> */
@@ -295,8 +296,8 @@ static inline char bw_phase_gen_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_phase_gen_state`.
@@ -360,7 +361,7 @@ struct bw_phase_gen_state {
 
 static inline void bw_phase_gen_init(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->portamento_coeffs);
 	coeffs->frequency = 1.f;
@@ -377,7 +378,7 @@ static inline void bw_phase_gen_init(
 static inline void bw_phase_gen_set_sample_rate(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -403,7 +404,7 @@ static inline void bw_phase_gen_do_update_coeffs_ctrl(
 
 static inline void bw_phase_gen_reset_coeffs(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_set_sample_rate);
 
@@ -425,13 +426,13 @@ static inline void bw_phase_gen_reset_state(
 		float                                   phase_0,
 		float * BW_RESTRICT                     y_0,
 		float * BW_RESTRICT                     y_inc_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(phase_0));
-	BW_ASSERT(y_0 != NULL);
-	BW_ASSERT(y_inc_0 != NULL);
+	BW_ASSERT(y_0 != BW_NULL);
+	BW_ASSERT(y_inc_0 != BW_NULL);
 	BW_ASSERT(y_0 != y_inc_0);
 
 	state->phase = phase_0;
@@ -456,20 +457,20 @@ static inline void bw_phase_gen_reset_state_multi(
 		float *                                              y_0,
 		float *                                              y_inc_0,
 		size_t                                               n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(phase_0 != NULL);
-	BW_ASSERT(y_0 != NULL && y_inc_0 != NULL ? y_0 != y_inc_0 : 1);
+	BW_ASSERT(phase_0 != BW_NULL);
+	BW_ASSERT(y_0 != BW_NULL && y_inc_0 != BW_NULL ? y_0 != y_inc_0 : 1);
 
-	if (y_0 != NULL) {
-		if (y_inc_0 != NULL) {
+	if (y_0 != BW_NULL) {
+		if (y_inc_0 != BW_NULL) {
 			for (size_t i = 0; i < n_channels; i++)
 				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], y_0 + i, y_inc_0 + i);
 		} else {
@@ -479,7 +480,7 @@ static inline void bw_phase_gen_reset_state_multi(
 			}
 		}
 	} else {
-		if (y_inc_0 != NULL) {
+		if (y_inc_0 != BW_NULL) {
 			for (size_t i = 0; i < n_channels; i++) {
 				float v;
 				bw_phase_gen_reset_state(coeffs, state[i], phase_0[i], &v, y_inc_0 + i);
@@ -494,13 +495,13 @@ static inline void bw_phase_gen_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
-	BW_ASSERT_DEEP(y_inc_0 != NULL ? bw_has_only_finite(y_inc_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_inc_0 != BW_NULL ? bw_has_only_finite(y_inc_0, n_channels) : 1);
 }
 
 static inline void bw_phase_gen_update_coeffs_ctrl(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 
@@ -512,7 +513,7 @@ static inline void bw_phase_gen_update_coeffs_ctrl(
 
 static inline void bw_phase_gen_update_coeffs_audio(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 
@@ -535,13 +536,13 @@ static inline void bw_phase_gen_process1(
 		bw_phase_gen_state * BW_RESTRICT        state,
 		float * BW_RESTRICT                     y,
 		float * BW_RESTRICT                     y_inc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
-	BW_ASSERT(y != NULL);
-	BW_ASSERT(y_inc != NULL);
+	BW_ASSERT(y != BW_NULL);
+	BW_ASSERT(y_inc != BW_NULL);
 	BW_ASSERT(y != y_inc);
 
 	*y_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state);
@@ -561,14 +562,14 @@ static inline void bw_phase_gen_process1_mod(
 		float                                   x_mod,
 		float * BW_RESTRICT                     y,
 		float * BW_RESTRICT                     y_inc) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x_mod));
-	BW_ASSERT(y != NULL);
-	BW_ASSERT(y_inc != NULL);
+	BW_ASSERT(y != BW_NULL);
+	BW_ASSERT(y_inc != BW_NULL);
 	BW_ASSERT(y != y_inc);
 
 	*y_inc = bw_one_pole_get_y_z1(&coeffs->portamento_state) * bw_pow2f(x_mod);
@@ -589,18 +590,18 @@ static inline void bw_phase_gen_process(
 		float *                           y,
 		float *                           y_inc,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(x_mod != NULL ? bw_has_only_finite(x_mod, n_samples) : 1);
-	BW_ASSERT(y != NULL && y_inc != NULL ? y != y_inc : 1);
+	BW_ASSERT_DEEP(x_mod != BW_NULL ? bw_has_only_finite(x_mod, n_samples) : 1);
+	BW_ASSERT(y != BW_NULL && y_inc != BW_NULL ? y != y_inc : 1);
 
 	bw_phase_gen_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
-		if (x_mod != NULL) {
-			if (y_inc != NULL)
+	if (y != BW_NULL) {
+		if (x_mod != BW_NULL) {
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], y + i, y_inc + i);
@@ -612,7 +613,7 @@ static inline void bw_phase_gen_process(
 					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], y + i, &v_phase_inc);
 				}
 		} else {
-			if (y_inc != NULL)
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					bw_phase_gen_process1(coeffs, state, y + i, y_inc + i);
@@ -625,8 +626,8 @@ static inline void bw_phase_gen_process(
 				}
 		}
 	} else {
-		if (x_mod != NULL) {
-			if (y_inc != NULL)
+		if (x_mod != BW_NULL) {
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					float v;
@@ -639,7 +640,7 @@ static inline void bw_phase_gen_process(
 					bw_phase_gen_process1_mod(coeffs, state, x_mod[i], &v, &v_phase_inc);
 				}
 		} else {
-			if (y_inc != NULL)
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					float v;
@@ -657,8 +658,8 @@ static inline void bw_phase_gen_process(
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_phase_gen_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
-	BW_ASSERT_DEEP(y_inc != NULL ? bw_has_only_finite(y_inc, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y_inc != BW_NULL ? bw_has_only_finite(y_inc, n_samples) : 1);
 }
 
 static inline void bw_phase_gen_process_multi(
@@ -669,32 +670,32 @@ static inline void bw_phase_gen_process_multi(
 		float * const *                                      y_inc,
 		size_t                                               n_channels,
 		size_t                                               n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y[i] != y[j]);
-	if (y_inc != NULL)
+	if (y_inc != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y_inc[i] != y_inc[j]);
-	if (y != NULL && y_inc != NULL)
+	if (y != BW_NULL && y_inc != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
 				BW_ASSERT(y[i] != y_inc[j]);
 #endif
 
 	bw_phase_gen_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
-		if (x_mod != NULL) {
-			if (y_inc != NULL)
+	if (y != BW_NULL) {
+		if (x_mod != BW_NULL) {
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -723,7 +724,7 @@ static inline void bw_phase_gen_process_multi(
 					}
 				}
 		} else {
-			if (y_inc != NULL)
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -747,8 +748,8 @@ static inline void bw_phase_gen_process_multi(
 				}
 		}
 	} else {
-		if (x_mod != NULL) {
-			if (y_inc != NULL)
+		if (x_mod != BW_NULL) {
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -773,7 +774,7 @@ static inline void bw_phase_gen_process_multi(
 					}
 				}
 		} else {
-			if (y_inc != NULL)
+			if (y_inc != BW_NULL)
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_phase_gen_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -801,7 +802,7 @@ static inline void bw_phase_gen_process_multi(
 static inline void bw_phase_gen_set_frequency(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
 		float                             value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -815,7 +816,7 @@ static inline void bw_phase_gen_set_frequency(
 static inline void bw_phase_gen_set_portamento_tau(
 		bw_phase_gen_coeffs * BW_RESTRICT coeffs,
 		float                             value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phase_gen_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phase_gen_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -829,7 +830,7 @@ static inline void bw_phase_gen_set_portamento_tau(
 
 static inline char bw_phase_gen_coeffs_is_valid(
 		const bw_phase_gen_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_phase_gen_coeffs"))
@@ -867,13 +868,13 @@ static inline char bw_phase_gen_coeffs_is_valid(
 static inline char bw_phase_gen_state_is_valid(
 		const bw_phase_gen_coeffs * BW_RESTRICT coeffs,
 		const bw_phase_gen_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_phase_gen_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_phaser.h b/include/bw_phaser.h
index ea7767d..8e44002 100644
--- a/include/bw_phaser.h
+++ b/include/bw_phaser.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_ap1 bw_common bw_lp1 bw_math bw_one_pole bw_osc_sin bw_phase_gen
  *  }}}
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input value to
@@ -145,7 +150,7 @@ static inline void bw_phaser_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_phaser_update_coeffs_ctrl()
  *  ```>>> */
@@ -267,8 +272,8 @@ static inline char bw_phaser_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_phaser_state`.
@@ -330,7 +335,7 @@ struct bw_phaser_state {
 
 static inline void bw_phaser_init(
 		bw_phaser_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_phase_gen_init(&coeffs->phase_gen_coeffs);
 	bw_ap1_init(&coeffs->ap1_coeffs);
@@ -349,7 +354,7 @@ static inline void bw_phaser_init(
 static inline void bw_phaser_set_sample_rate(
 		bw_phaser_coeffs * BW_RESTRICT coeffs,
 		float                          sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -366,7 +371,7 @@ static inline void bw_phaser_set_sample_rate(
 
 static inline void bw_phaser_reset_coeffs(
 		bw_phaser_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_set_sample_rate);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
@@ -389,10 +394,10 @@ static inline float bw_phaser_reset_state(
 		const bw_phaser_coeffs * BW_RESTRICT coeffs,
 		bw_phaser_state * BW_RESTRICT        state,
 		float                                x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float y = bw_ap1_reset_state(&coeffs->ap1_coeffs, &state->ap1_state[0], x_0);
@@ -418,18 +423,18 @@ static inline void bw_phaser_reset_state_multi(
 		const float *                                     x_0,
 		float *                                           y_0,
 		size_t                                            n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_phaser_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -438,12 +443,12 @@ static inline void bw_phaser_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_phaser_update_coeffs_ctrl(
 		bw_phaser_coeffs *BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
@@ -456,7 +461,7 @@ static inline void bw_phaser_update_coeffs_ctrl(
 
 static inline void bw_phaser_update_coeffs_audio(
 		bw_phaser_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
@@ -477,11 +482,11 @@ static inline float bw_phaser_process1(
 		const bw_phaser_coeffs * BW_RESTRICT coeffs,
 		bw_phaser_state * BW_RESTRICT        state,
 		float                                x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -504,15 +509,15 @@ static inline void bw_phaser_process(
 		const float *                  x,
 		float *                        y,
 		size_t                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_phaser_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -533,18 +538,18 @@ static inline void bw_phaser_process_multi(
 		float * const *                                   y,
 		size_t                                            n_channels,
 		size_t                                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(coeffs->center * bw_pow2f(coeffs->amount) >= 1e-6f && coeffs->center * bw_pow2f(coeffs->amount) <= 1e12f);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -565,7 +570,7 @@ static inline void bw_phaser_process_multi(
 static inline void bw_phaser_set_rate(
 		bw_phaser_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -579,7 +584,7 @@ static inline void bw_phaser_set_rate(
 static inline void bw_phaser_set_center(
 		bw_phaser_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -594,7 +599,7 @@ static inline void bw_phaser_set_center(
 static inline void bw_phaser_set_amount(
 		bw_phaser_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_phaser_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_phaser_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -608,7 +613,7 @@ static inline void bw_phaser_set_amount(
 
 static inline char bw_phaser_coeffs_is_valid(
 		const bw_phaser_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_phaser_coeffs"))
@@ -636,20 +641,20 @@ static inline char bw_phaser_coeffs_is_valid(
 static inline char bw_phaser_state_is_valid(
 		const bw_phaser_coeffs * BW_RESTRICT coeffs,
 		const bw_phaser_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_phaser_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : NULL, &state->ap1_state[0])
-		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : NULL, &state->ap1_state[1])
-		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : NULL, &state->ap1_state[2])
-		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : NULL, &state->ap1_state[3]);
+	return bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : BW_NULL, &state->ap1_state[0])
+		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : BW_NULL, &state->ap1_state[1])
+		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : BW_NULL, &state->ap1_state[2])
+		&& bw_ap1_state_is_valid(coeffs ? &coeffs->ap1_coeffs : BW_NULL, &state->ap1_state[3]);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_pink_filt.h b/include/bw_pink_filt.h
index ac47bdf..7f571ce 100644
--- a/include/bw_pink_filt.h
+++ b/include/bw_pink_filt.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Pinking filter.
@@ -40,6 +40,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_pink_filt_reset_coeffs()</code>,
@@ -175,7 +180,7 @@ static inline void bw_pink_filt_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_pink_filt_update_coeffs_ctrl()
  *  ```>>> */
@@ -290,8 +295,8 @@ static inline char bw_pink_filt_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_pink_filt_state`.
@@ -348,7 +353,7 @@ struct bw_pink_filt_state {
 
 static inline void bw_pink_filt_init(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->sample_rate_scaling = 0;
 
@@ -364,7 +369,7 @@ static inline void bw_pink_filt_init(
 static inline void bw_pink_filt_set_sample_rate(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -380,7 +385,7 @@ static inline void bw_pink_filt_set_sample_rate(
 
 static inline void bw_pink_filt_reset_coeffs(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_set_sample_rate);
 
@@ -398,10 +403,10 @@ static inline float bw_pink_filt_reset_state(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		bw_pink_filt_state * BW_RESTRICT        state,
 		float                                   x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	(void)coeffs;
@@ -429,18 +434,18 @@ static inline void bw_pink_filt_reset_state_multi(
 		const float *                                        x_0,
 		float *                                              y_0,
 		size_t                                               n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_pink_filt_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -449,12 +454,12 @@ static inline void bw_pink_filt_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_pink_filt_update_coeffs_ctrl(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
 
@@ -463,7 +468,7 @@ static inline void bw_pink_filt_update_coeffs_ctrl(
 
 static inline void bw_pink_filt_update_coeffs_audio(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
 
@@ -474,10 +479,10 @@ static inline float bw_pink_filt_process1(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		bw_pink_filt_state * BW_RESTRICT        state,
 		float                                   x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -503,10 +508,10 @@ static inline float bw_pink_filt_process1_scaling(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		bw_pink_filt_state * BW_RESTRICT        state,
 		float                                   x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -526,14 +531,14 @@ static inline void bw_pink_filt_process(
 		const float *                     x,
 		float *                           y,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->sample_rate_scaling)
 		for (size_t i = 0; i < n_samples; i++)
@@ -555,17 +560,17 @@ static inline void bw_pink_filt_process_multi(
 		float * const *                                      y,
 		size_t                                               n_channels,
 		size_t                                               n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -582,7 +587,7 @@ static inline void bw_pink_filt_process_multi(
 static inline void bw_pink_filt_set_sample_rate_scaling(
 		bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		char                              value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_init);
 
@@ -594,7 +599,7 @@ static inline void bw_pink_filt_set_sample_rate_scaling(
 
 static inline float bw_pink_filt_get_scaling_k(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_pink_filt_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_pink_filt_coeffs_state_set_sample_rate);
 
@@ -603,7 +608,7 @@ static inline float bw_pink_filt_get_scaling_k(
 
 static inline char bw_pink_filt_coeffs_is_valid(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_pink_filt_coeffs"))
@@ -623,13 +628,13 @@ static inline char bw_pink_filt_coeffs_is_valid(
 static inline char bw_pink_filt_state_is_valid(
 		const bw_pink_filt_coeffs * BW_RESTRICT coeffs,
 		const bw_pink_filt_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_pink_filt_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_ppm.h b/include/bw_ppm.h
index be3b7a9..7b736b5 100644
--- a/include/bw_ppm.h
+++ b/include/bw_ppm.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_env_follow bw_math bw_one_pole }}}
  *  description {{{
  *    Digital peak programme meter with adjustable integration time constant.
@@ -30,6 +30,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Enforced minimum output value <code>-600.f</code>.</li>
@@ -144,7 +149,7 @@ static inline void bw_ppm_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_ppm_update_coeffs_ctrl()
  *  ```>>> */
@@ -186,7 +191,7 @@ static inline void bw_ppm_process(
  *
  *    Output sample values are in dBFS (minimum `-600.f`).
  *
- *    `y` may be `NULL`.
+ *    `y` may be `BW_NULL`.
  *
  *    #### bw_ppm_process_multi()
  *  ```>>> */
@@ -205,7 +210,7 @@ static inline void bw_ppm_process_multi(
  *
  *    Output sample values are in dBFS (minimum `-600.f`).
  *
- *    `y` or any element of `y` may be `NULL`.
+ *    `y` or any element of `y` may be `BW_NULL`.
  *
  *    #### bw_ppm_set_integration_time()
  *  ```>>> */
@@ -248,8 +253,8 @@ static inline char bw_ppm_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_ppm_state`.
@@ -304,7 +309,7 @@ struct bw_ppm_state {
 
 static inline void bw_ppm_init(
 		bw_ppm_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_env_follow_init(&coeffs->env_follow_coeffs);
 	bw_env_follow_set_release_tau(&coeffs->env_follow_coeffs, 0.738300619235528f);
@@ -321,7 +326,7 @@ static inline void bw_ppm_init(
 static inline void bw_ppm_set_sample_rate(
 		bw_ppm_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -337,7 +342,7 @@ static inline void bw_ppm_set_sample_rate(
 
 static inline void bw_ppm_reset_coeffs(
 		bw_ppm_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_set_sample_rate);
 
@@ -355,10 +360,10 @@ static inline float bw_ppm_reset_state(
 		const bw_ppm_coeffs * BW_RESTRICT coeffs,
 		bw_ppm_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float yl = bw_env_follow_reset_state(&coeffs->env_follow_coeffs, &state->env_follow_state, x_0);
@@ -383,18 +388,18 @@ static inline void bw_ppm_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_ppm_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -403,12 +408,12 @@ static inline void bw_ppm_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_ppm_update_coeffs_ctrl(
 		bw_ppm_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
 
@@ -420,7 +425,7 @@ static inline void bw_ppm_update_coeffs_ctrl(
 
 static inline void bw_ppm_update_coeffs_audio(
 		bw_ppm_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
 
@@ -434,10 +439,10 @@ static inline float bw_ppm_process1(
 		const bw_ppm_coeffs * BW_RESTRICT coeffs,
 		bw_ppm_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -459,16 +464,16 @@ static inline void bw_ppm_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
 
 	bw_ppm_update_coeffs_ctrl(coeffs);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++) {
 			bw_ppm_update_coeffs_audio(coeffs);
 			y[i] = bw_ppm_process1(coeffs, state, x[i]);
@@ -482,7 +487,7 @@ static inline void bw_ppm_process(
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_ppm_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
 }
 
 static inline void bw_ppm_process_multi(
@@ -492,30 +497,30 @@ static inline void bw_ppm_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
+				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 #endif
 
 	bw_ppm_update_coeffs_ctrl(coeffs);
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_samples; i++) {
 			bw_ppm_update_coeffs_audio(coeffs);
 			for (size_t j = 0; j < n_channels; j++) {
 				const float v = bw_ppm_process1(coeffs, state[j], x[j][i]);
-				if (y[j] != NULL)
+				if (y[j] != BW_NULL)
 					y[j][i] = v;
 			}
 		}
@@ -533,7 +538,7 @@ static inline void bw_ppm_process_multi(
 static inline void bw_ppm_set_integration_tau(
 		bw_ppm_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ppm_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ppm_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -546,15 +551,15 @@ static inline void bw_ppm_set_integration_tau(
 }
 
 static inline float bw_ppm_get_y_z1(const bw_ppm_state *BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_ppm_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_ppm_state_is_valid(BW_NULL, state));
 
 	return state->y_z1;
 }
 
 static inline char bw_ppm_coeffs_is_valid(
 		const bw_ppm_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ppm_coeffs"))
@@ -569,20 +574,20 @@ static inline char bw_ppm_coeffs_is_valid(
 static inline char bw_ppm_state_is_valid(
 		const bw_ppm_coeffs * BW_RESTRICT coeffs,
 		const bw_ppm_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_ppm_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
 	if (!bw_is_finite(state->y_z1) || state->y_z1 < -600.f)
 		return 0.f;
 
-	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : NULL, &state->env_follow_state);
+	return bw_env_follow_state_is_valid(coeffs ? &coeffs->env_follow_coeffs : BW_NULL, &state->env_follow_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_rand.h b/include/bw_rand.h
index d2711b9..b945daf 100644
--- a/include/bw_rand.h
+++ b/include/bw_rand.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Pseudo-random number generators.
@@ -42,6 +42,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added one more assertion in <code>bw_randf()</code>.</li>
@@ -119,7 +124,7 @@ extern "C" {
 
 static inline uint32_t bw_randu32(
 		uint64_t * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	// Permuted Congruential Generator,
 	// taken from https://nullprogram.com/blog/2017/09/21/
 	*state = *state * 0x9b60933458e17d7d + 0xd737232eeccdf7ed;
@@ -128,7 +133,7 @@ static inline uint32_t bw_randu32(
 
 static inline float bw_randf(
 		uint64_t * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	const float y = (2.f / (float)UINT32_MAX) * (float)bw_randu32(state) - 1.f;
 	BW_ASSERT(bw_is_finite(y));
 	return y;
diff --git a/include/bw_reverb.h b/include/bw_reverb.h
index 4cba914..33dbe20 100644
--- a/include/bw_reverb.h
+++ b/include/bw_reverb.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_buf bw_common bw_delay bw_dry_wet bw_gain bw_lp1 bw_math bw_one_pole
  *    bw_osc_sin bw_phase_gen
@@ -35,6 +35,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial value arguments in
@@ -170,7 +175,7 @@ static inline void bw_reverb_reset_state_multi(
  *    (left) and `x_r_0` (right) arrays.
  *
  *    The corresponding initial output values are written into the `y_l_0`
- *    (left) and `y_r_0` arrays, if each is not `NULL`.
+ *    (left) and `y_r_0` arrays, if each is not `BW_NULL`.
  *
  *    #### bw_reverb_update_coeffs_ctrl()
  *  ```>>> */
@@ -316,8 +321,8 @@ static inline char bw_reverb_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_reverb_state`.
@@ -455,7 +460,7 @@ struct bw_reverb_state {
 
 static inline void bw_reverb_init(
 		bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_delay_init(&coeffs->predelay_coeffs, 0.1f);
 	bw_lp1_init(&coeffs->bandwidth_coeffs);
@@ -498,7 +503,7 @@ static inline void bw_reverb_init(
 static inline void bw_reverb_set_sample_rate(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -559,7 +564,7 @@ static inline void bw_reverb_set_sample_rate(
 
 static inline size_t bw_reverb_mem_req(
 		const bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_set_sample_rate);
 
@@ -582,11 +587,11 @@ static inline void bw_reverb_mem_set(
 		const bw_reverb_coeffs * BW_RESTRICT coeffs,
 		bw_reverb_state * BW_RESTRICT        state,
 		void * BW_RESTRICT                   mem) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_set_sample_rate);
-	BW_ASSERT(state != NULL);
-	BW_ASSERT(mem != NULL);
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT(mem != BW_NULL);
 
 	char *m = (char *)mem;
 	bw_delay_mem_set(&coeffs->predelay_coeffs, &state->predelay_state, m);
@@ -627,7 +632,7 @@ static inline void bw_reverb_mem_set(
 
 static inline void bw_reverb_reset_coeffs(
 		bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_set_sample_rate);
 
@@ -671,16 +676,16 @@ static inline void bw_reverb_reset_state(
 		float                                x_r_0,
 		float * BW_RESTRICT                  y_l_0,
 		float * BW_RESTRICT                  y_r_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_reverb_state_state_mem_set);
 	BW_ASSERT(bw_is_finite(x_l_0));
 	BW_ASSERT(bw_is_finite(x_r_0));
-	BW_ASSERT(y_l_0 != NULL);
-	BW_ASSERT(y_r_0 != NULL);
+	BW_ASSERT(y_l_0 != BW_NULL);
+	BW_ASSERT(y_r_0 != BW_NULL);
 	BW_ASSERT(y_l_0 != y_r_0);
 
 	const float i = 0.5f * (x_l_0 + x_r_0);
@@ -739,21 +744,21 @@ static inline void bw_reverb_reset_state_multi(
 		float *                                           y_l_0,
 		float *                                           y_r_0,
 		size_t                                            n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_l_0 != NULL);
-	BW_ASSERT(x_r_0 != NULL);
-	BW_ASSERT(y_l_0 != NULL && y_r_0 != NULL ? y_l_0 != y_r_0 : 1);
+	BW_ASSERT(x_l_0 != BW_NULL);
+	BW_ASSERT(x_r_0 != BW_NULL);
+	BW_ASSERT(y_l_0 != BW_NULL && y_r_0 != BW_NULL ? y_l_0 != y_r_0 : 1);
 
-	if (y_l_0 != NULL) {
-		if (y_r_0 != NULL) {
+	if (y_l_0 != BW_NULL) {
+		if (y_r_0 != BW_NULL) {
 			for (size_t i = 0; i < n_channels; i++)
 				bw_reverb_reset_state(coeffs, state[i], x_l_0[i], x_r_0[i], y_l_0 + i, y_r_0 + i);
 		} else {
@@ -762,7 +767,7 @@ static inline void bw_reverb_reset_state_multi(
 				bw_reverb_reset_state(coeffs, state[i], x_l_0[i], x_r_0[i], y_l_0 + i, &yr);
 		}
 	} else {
-		if (y_r_0 != NULL) {
+		if (y_r_0 != BW_NULL) {
 			float yl;
 			for (size_t i = 0; i < n_channels; i++)
 				bw_reverb_reset_state(coeffs, state[i], x_l_0[i], x_r_0[i], &yl, y_r_0 + i);
@@ -775,13 +780,13 @@ static inline void bw_reverb_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_l_0 != NULL ? bw_has_only_finite(y_l_0, n_channels) : 1);
-	BW_ASSERT_DEEP(y_r_0 != NULL ? bw_has_only_finite(y_r_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_l_0 != BW_NULL ? bw_has_only_finite(y_l_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_r_0 != BW_NULL ? bw_has_only_finite(y_r_0, n_channels) : 1);
 }
 
 static inline void bw_reverb_update_coeffs_ctrl(
 		bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
 
@@ -797,7 +802,7 @@ static inline void bw_reverb_update_coeffs_ctrl(
 
 static inline void bw_reverb_update_coeffs_audio(
 		bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
 
@@ -827,16 +832,16 @@ static inline void bw_reverb_process1(
 		float                                x_r,
 		float *                              y_l,
 		float *                              y_r) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_reverb_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x_l));
 	BW_ASSERT(bw_is_finite(x_r));
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 
 	const float i = 0.5f * (x_l + x_r);
@@ -936,18 +941,18 @@ static inline void bw_reverb_process(
 		float *                        y_l,
 		float *                        y_r,
 		size_t                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_state_is_valid(coeffs, state));
 	BW_ASSERT_DEEP(state->state >= bw_reverb_state_state_reset_state);
-	BW_ASSERT(x_l != NULL);
+	BW_ASSERT(x_l != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_l, n_samples));
-	BW_ASSERT(x_r != NULL);
+	BW_ASSERT(x_r != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_r, n_samples));
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 
 	bw_reverb_update_coeffs_ctrl(coeffs);
@@ -973,19 +978,19 @@ static inline void bw_reverb_process_multi(
 		float * const *                                   y_r,
 		size_t                                            n_channels,
 		size_t                                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_l != NULL);
-	BW_ASSERT(x_r != NULL);
-	BW_ASSERT(y_l != NULL);
-	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(x_l != BW_NULL);
+	BW_ASSERT(x_r != BW_NULL);
+	BW_ASSERT(y_l != BW_NULL);
+	BW_ASSERT(y_r != BW_NULL);
 	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
@@ -1012,7 +1017,7 @@ static inline void bw_reverb_process_multi(
 static inline void bw_reverb_set_predelay(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -1027,7 +1032,7 @@ static inline void bw_reverb_set_predelay(
 static inline void bw_reverb_set_bandwidth(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -1042,7 +1047,7 @@ static inline void bw_reverb_set_bandwidth(
 static inline void bw_reverb_set_damping(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -1057,7 +1062,7 @@ static inline void bw_reverb_set_damping(
 static inline void bw_reverb_set_decay(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -1072,7 +1077,7 @@ static inline void bw_reverb_set_decay(
 static inline void bw_reverb_set_wet(
 		bw_reverb_coeffs * BW_RESTRICT coeffs,
 		float                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_reverb_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_reverb_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -1086,7 +1091,7 @@ static inline void bw_reverb_set_wet(
 
 static inline char bw_reverb_coeffs_is_valid(
 		const bw_reverb_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_reverb_coeffs"))
@@ -1145,7 +1150,7 @@ static inline char bw_reverb_coeffs_is_valid(
 static inline char bw_reverb_state_is_valid(
 		const bw_reverb_coeffs * BW_RESTRICT coeffs,
 		const bw_reverb_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_reverb_state"))
@@ -1154,29 +1159,29 @@ static inline char bw_reverb_state_is_valid(
 		return 0;
 
 	if (state->state >= bw_reverb_state_state_reset_state) {
-		if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+		if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 			return 0;
 
-		if (!bw_lp1_state_is_valid(coeffs ? &coeffs->bandwidth_coeffs : NULL, &state->bandwidth_state)
-			|| !bw_lp1_state_is_valid(coeffs ? &coeffs->damping_coeffs : NULL, &state->damping_1_state)
-			|| !bw_lp1_state_is_valid(coeffs ? &coeffs->damping_coeffs : NULL, &state->damping_2_state))
+		if (!bw_lp1_state_is_valid(coeffs ? &coeffs->bandwidth_coeffs : BW_NULL, &state->bandwidth_state)
+			|| !bw_lp1_state_is_valid(coeffs ? &coeffs->damping_coeffs : BW_NULL, &state->damping_1_state)
+			|| !bw_lp1_state_is_valid(coeffs ? &coeffs->damping_coeffs : BW_NULL, &state->damping_2_state))
 			return 0;
 	}
 #endif
 
-	return bw_delay_state_is_valid(coeffs ? &coeffs->predelay_coeffs : NULL, &state->predelay_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id1_coeffs : NULL, &state->delay_id1_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id2_coeffs : NULL, &state->delay_id2_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id3_coeffs : NULL, &state->delay_id3_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id4_coeffs : NULL, &state->delay_id4_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd1_coeffs : NULL, &state->delay_dd1_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd2_coeffs : NULL, &state->delay_dd2_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd3_coeffs : NULL, &state->delay_dd3_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd4_coeffs : NULL, &state->delay_dd4_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d1_coeffs : NULL, &state->delay_d1_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d2_coeffs : NULL, &state->delay_d2_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d3_coeffs : NULL, &state->delay_d3_state)
-		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d4_coeffs : NULL, &state->delay_d4_state);
+	return bw_delay_state_is_valid(coeffs ? &coeffs->predelay_coeffs : BW_NULL, &state->predelay_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id1_coeffs : BW_NULL, &state->delay_id1_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id2_coeffs : BW_NULL, &state->delay_id2_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id3_coeffs : BW_NULL, &state->delay_id3_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_id4_coeffs : BW_NULL, &state->delay_id4_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd1_coeffs : BW_NULL, &state->delay_dd1_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd2_coeffs : BW_NULL, &state->delay_dd2_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd3_coeffs : BW_NULL, &state->delay_dd3_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_dd4_coeffs : BW_NULL, &state->delay_dd4_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d1_coeffs : BW_NULL, &state->delay_d1_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d2_coeffs : BW_NULL, &state->delay_d2_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d3_coeffs : BW_NULL, &state->delay_d3_state)
+		&& bw_delay_state_is_valid(coeffs ? &coeffs->delay_d4_coeffs : BW_NULL, &state->delay_d4_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_ring_mod.h b/include/bw_ring_mod.h
index 5c461bc..08f2b4a 100644
--- a/include/bw_ring_mod.h
+++ b/include/bw_ring_mod.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Ring modulator with variable modulation amount.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Module renamed as bw_ring_mod.</li>
@@ -226,7 +231,7 @@ struct bw_ring_mod_coeffs {
 
 static inline void bw_ring_mod_init(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.05f);
@@ -243,7 +248,7 @@ static inline void bw_ring_mod_init(
 static inline void bw_ring_mod_set_sample_rate(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs,
 		float                            sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -260,7 +265,7 @@ static inline void bw_ring_mod_set_sample_rate(
 
 static inline void bw_ring_mod_reset_coeffs(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_set_sample_rate);
 
@@ -275,7 +280,7 @@ static inline void bw_ring_mod_reset_coeffs(
 
 static inline void bw_ring_mod_update_coeffs_ctrl(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_reset_coeffs);
 
@@ -284,7 +289,7 @@ static inline void bw_ring_mod_update_coeffs_ctrl(
 
 static inline void bw_ring_mod_update_coeffs_audio(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_reset_coeffs);
 
@@ -298,7 +303,7 @@ static inline float bw_ring_mod_process1(
 		const bw_ring_mod_coeffs * BW_RESTRICT coeffs,
 		float                                  x_mod,
 		float                                  x_car) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_reset_coeffs);
 	BW_ASSERT(bw_is_finite(x_mod));
@@ -320,14 +325,14 @@ static inline void bw_ring_mod_process(
 		const float *                    x_car,
 		float *                          y,
 		size_t                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_mod != NULL);
+	BW_ASSERT(x_mod != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_mod, n_samples));
-	BW_ASSERT(x_car != NULL);
+	BW_ASSERT(x_car != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x_car, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_ring_mod_update_coeffs_audio(coeffs);
@@ -346,12 +351,12 @@ static inline void bw_ring_mod_process_multi(
 		float * const *                  y,
 		size_t                           n_channels,
 		size_t                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_reset_coeffs);
-	BW_ASSERT(x_mod != NULL);
-	BW_ASSERT(x_car != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x_mod != BW_NULL);
+	BW_ASSERT(x_car != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -371,7 +376,7 @@ static inline void bw_ring_mod_process_multi(
 static inline void bw_ring_mod_set_amount(
 		bw_ring_mod_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_ring_mod_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_ring_mod_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -385,7 +390,7 @@ static inline void bw_ring_mod_set_amount(
 
 static inline char bw_ring_mod_coeffs_is_valid(
 		const bw_ring_mod_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_ring_mod_coeffs"))
diff --git a/include/bw_satur.h b/include/bw_satur.h
index 64ec75a..149a16b 100644
--- a/include/bw_satur.h
+++ b/include/bw_satur.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Antialiased tanh-based saturation with parametric bias and gain
@@ -45,6 +45,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Changed default value for gain compensation to off.</li>
@@ -166,7 +171,7 @@ static inline void bw_satur_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_satur_update_coeffs_ctrl()
  *  ```>>> */
@@ -288,8 +293,8 @@ static inline char bw_satur_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_satur_state`.
@@ -362,7 +367,7 @@ static inline float bw_satur_tanhf(
 
 static inline void bw_satur_init(
 		bw_satur_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -383,7 +388,7 @@ static inline void bw_satur_init(
 static inline void bw_satur_set_sample_rate(
 		bw_satur_coeffs * BW_RESTRICT coeffs,
 		float                         sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -415,7 +420,7 @@ static inline void bw_satur_do_update_coeffs(
 
 static inline void bw_satur_reset_coeffs(
 		bw_satur_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_set_sample_rate);
 
@@ -435,10 +440,10 @@ static inline float bw_satur_reset_state(
 		const bw_satur_coeffs * BW_RESTRICT coeffs,
 		bw_satur_state * BW_RESTRICT        state,
 		float                               x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	const float x = bw_one_pole_get_y_z1(&coeffs->smooth_gain_state) * x_0 + bw_one_pole_get_y_z1(&coeffs->smooth_bias_state);
@@ -467,18 +472,18 @@ static inline void bw_satur_reset_state_multi(
 		const float *                                    x_0,
 		float *                                          y_0,
 		size_t                                           n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_satur_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -487,12 +492,12 @@ static inline void bw_satur_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_satur_update_coeffs_ctrl(
 		bw_satur_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
 
@@ -501,7 +506,7 @@ static inline void bw_satur_update_coeffs_ctrl(
 
 static inline void bw_satur_update_coeffs_audio(
 		bw_satur_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
 
@@ -515,10 +520,10 @@ static inline float bw_satur_process1(
 		const bw_satur_coeffs * BW_RESTRICT coeffs,
 		bw_satur_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -543,10 +548,10 @@ static inline float bw_satur_process1_comp(
 		const bw_satur_coeffs * BW_RESTRICT coeffs,
 		bw_satur_state * BW_RESTRICT        state,
 		float                               x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -566,14 +571,14 @@ static inline void bw_satur_process(
 		const float *                 x,
 		float *                       y,
 		size_t                        n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	if (coeffs->gain_compensation)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -599,17 +604,17 @@ static inline void bw_satur_process_multi(
 		float * const *                                  y,
 		size_t                                           n_channels,
 		size_t                                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -630,7 +635,7 @@ static inline void bw_satur_process_multi(
 static inline void bw_satur_set_bias(
 		bw_satur_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -645,7 +650,7 @@ static inline void bw_satur_set_bias(
 static inline void bw_satur_set_gain(
 		bw_satur_coeffs * BW_RESTRICT coeffs,
 		float                         value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -660,7 +665,7 @@ static inline void bw_satur_set_gain(
 static inline void bw_satur_set_gain_compensation(
 		bw_satur_coeffs * BW_RESTRICT coeffs,
 		char                          value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_satur_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_satur_coeffs_state_init);
 
@@ -672,7 +677,7 @@ static inline void bw_satur_set_gain_compensation(
 
 static inline char bw_satur_coeffs_is_valid(
 		const bw_satur_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_satur_coeffs"))
@@ -709,13 +714,13 @@ static inline char bw_satur_coeffs_is_valid(
 static inline char bw_satur_state_is_valid(
 		const bw_satur_coeffs * BW_RESTRICT coeffs,
 		const bw_satur_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_satur_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_slew_lim.h b/include/bw_slew_lim.h
index afe3a4a..c695023 100644
--- a/include/bw_slew_lim.h
+++ b/include/bw_slew_lim.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Slew-rate limiter with separate maximum increasing and decreasing rates.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_slew_lim_reset_state_multi()</code> and updated
@@ -150,7 +155,7 @@ static inline void bw_slew_lim_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the
- *    `y_0` array, if not `NULL`.
+ *    `y_0` array, if not `BW_NULL`.
  *
  *    #### bw_slew_lim_update_coeffs_ctrl()
  *  ```>>> */
@@ -219,7 +224,7 @@ static inline void bw_slew_lim_process(
  *    first `n_samples` of the output buffer `y`, while using and updating both
  *    `coeffs` and `state` (control and audio rate).
  *
- *    `y` may be `NULL`.
+ *    `y` may be `BW_NULL`.
  *
  *    #### bw_slew_lim_process_multi()
  *  ```>>> */
@@ -236,7 +241,7 @@ static inline void bw_slew_lim_process_multi(
  *    using and updating both the common `coeffs` and each of the `n_channels`
  *    `state`s (control and audio rate).
  *
- *    `y` or any element of `y` may be `NULL`.
+ *    `y` or any element of `y` may be `BW_NULL`.
  *
  *    #### bw_slew_lim_set_max_rate()
  *  ```>>> */
@@ -316,8 +321,8 @@ static inline char bw_slew_lim_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_slew_lim_state`.
@@ -377,7 +382,7 @@ struct bw_slew_lim_state {
 
 static inline void bw_slew_lim_init(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->max_rate_up = INFINITY;
 	coeffs->max_rate_down = INFINITY;
@@ -394,7 +399,7 @@ static inline void bw_slew_lim_init(
 static inline void bw_slew_lim_set_sample_rate(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		float                            sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -417,7 +422,7 @@ static inline void bw_slew_lim_do_update_coeffs_ctrl(
 
 static inline void bw_slew_lim_reset_coeffs(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_set_sample_rate);
 
@@ -435,10 +440,10 @@ static inline float bw_slew_lim_reset_state(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		bw_slew_lim_state * BW_RESTRICT        state,
 		float                                  x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	(void)coeffs;
@@ -463,18 +468,18 @@ static inline void bw_slew_lim_reset_state_multi(
 		const float *                                       x_0,
 		float *                                             y_0,
 		size_t                                              n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_slew_lim_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -483,12 +488,12 @@ static inline void bw_slew_lim_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_slew_lim_update_coeffs_ctrl(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
 
@@ -500,7 +505,7 @@ static inline void bw_slew_lim_update_coeffs_ctrl(
 
 static inline void bw_slew_lim_update_coeffs_audio(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
 
@@ -511,10 +516,10 @@ static inline float bw_slew_lim_process1(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		bw_slew_lim_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 	BW_ASSERT(bw_is_finite(coeffs->max_inc) && bw_is_finite(coeffs->max_dec));
@@ -534,10 +539,10 @@ static inline float bw_slew_lim_process1_up(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		bw_slew_lim_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 	BW_ASSERT(bw_is_finite(coeffs->max_inc));
@@ -557,10 +562,10 @@ static inline float bw_slew_lim_process1_down(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		bw_slew_lim_state * BW_RESTRICT        state,
 		float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 	BW_ASSERT(bw_is_finite(coeffs->max_dec));
@@ -580,10 +585,10 @@ static inline float bw_slew_lim_process1_none(
 	const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 	bw_slew_lim_state * BW_RESTRICT        state,
 	float                                  x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -603,16 +608,16 @@ static inline void bw_slew_lim_process(
 		const float *                    x,
 		float *                          y,
 		size_t                           n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
 
 	bw_slew_lim_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
+	if (y != BW_NULL) {
 		if (coeffs->max_rate_up != INFINITY) {
 			if (coeffs->max_rate_down != INFINITY)
 				for (size_t i = 0; i < n_samples; i++)
@@ -650,7 +655,7 @@ static inline void bw_slew_lim_process(
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y != NULL ? bw_has_only_finite(y, n_samples) : 1);
+	BW_ASSERT_DEEP(y != BW_NULL ? bw_has_only_finite(y, n_samples) : 1);
 }
 
 static inline void bw_slew_lim_process_multi(
@@ -660,29 +665,29 @@ static inline void bw_slew_lim_process_multi(
 		float * const *                                     y,
 		size_t                                              n_channels,
 		size_t                                              n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != NULL)
+	if (y != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
+				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 #endif
 
 	bw_slew_lim_update_coeffs_ctrl(coeffs);
-	if (y != NULL) {
+	if (y != BW_NULL) {
 		if (coeffs->max_rate_up != INFINITY) {
 			if (coeffs->max_rate_down != INFINITY)
 				for (size_t j = 0; j < n_channels; j++)
-					if (y[j] != NULL)
+					if (y[j] != BW_NULL)
 						for (size_t i = 0; i < n_samples; i++)
 							y[j][i] = bw_slew_lim_process1(coeffs, state[j], x[j][i]);
 					else
@@ -691,14 +696,14 @@ static inline void bw_slew_lim_process_multi(
 			else
 				for (size_t j = 0; j < n_channels; j++)
 					for (size_t i = 0; i < n_samples; i++)
-						if (y[j] != NULL)
+						if (y[j] != BW_NULL)
 							y[j][i] = bw_slew_lim_process1_up(coeffs, state[j], x[j][i]);
 						else
 							bw_slew_lim_process1_up(coeffs, state[j], x[j][i]);
 		} else {
 			if (coeffs->max_rate_down != INFINITY)
 				for (size_t j = 0; j < n_channels; j++)
-					if (y[j] != NULL)
+					if (y[j] != BW_NULL)
 						for (size_t i = 0; i < n_samples; i++)
 							y[j][i] = bw_slew_lim_process1_down(coeffs, state[j], x[j][i]);
 					else
@@ -706,18 +711,18 @@ static inline void bw_slew_lim_process_multi(
 							bw_slew_lim_process1_down(coeffs, state[j], x[j][i]);
 			else
 				for (size_t j = 0; j < n_channels; j++) {
-					BW_ASSERT(state[j] != NULL);
+					BW_ASSERT(state[j] != BW_NULL);
 					BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state[j]));
-					BW_ASSERT(x[j] != NULL);
+					BW_ASSERT(x[j] != BW_NULL);
 					BW_ASSERT_DEEP(bw_has_only_finite(x[j], n_samples));
 
-					if (y[j] != NULL)
+					if (y[j] != BW_NULL)
 						for (size_t i = 0; i < n_samples; i++)
 							y[j][i] = x[j][i];
 					state[j]->y_z1 = x[j][n_samples - 1];
 
 					BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state[j]));
-					BW_ASSERT_DEEP(y[j] != NULL ? bw_has_only_finite(y[j], n_samples) : 1);
+					BW_ASSERT_DEEP(y[j] != BW_NULL ? bw_has_only_finite(y[j], n_samples) : 1);
 				}
 		}
 	} else {
@@ -737,9 +742,9 @@ static inline void bw_slew_lim_process_multi(
 						bw_slew_lim_process1_down(coeffs, state[j], x[j][i]);
 			else
 				for (size_t j = 0; j < n_channels; j++) {
-					BW_ASSERT(state[j] != NULL);
+					BW_ASSERT(state[j] != BW_NULL);
 					BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(coeffs, state[j]));
-					BW_ASSERT(x[j] != NULL);
+					BW_ASSERT(x[j] != BW_NULL);
 					BW_ASSERT_DEEP(bw_has_only_finite(x[j], n_samples));
 
 					state[j]->y_z1 = x[j][n_samples - 1];
@@ -756,7 +761,7 @@ static inline void bw_slew_lim_process_multi(
 static inline void bw_slew_lim_set_max_rate(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -772,7 +777,7 @@ static inline void bw_slew_lim_set_max_rate(
 static inline void bw_slew_lim_set_max_rate_up(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -787,7 +792,7 @@ static inline void bw_slew_lim_set_max_rate_up(
 static inline void bw_slew_lim_set_max_rate_down(
 		bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		float                            value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_slew_lim_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_slew_lim_coeffs_state_init);
 	BW_ASSERT(!bw_is_nan(value));
@@ -801,15 +806,15 @@ static inline void bw_slew_lim_set_max_rate_down(
 
 static inline float bw_slew_lim_get_y_z1(
 		const bw_slew_lim_state * BW_RESTRICT state) {
-	BW_ASSERT(state != NULL);
-	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(NULL, state));
+	BW_ASSERT(state != BW_NULL);
+	BW_ASSERT_DEEP(bw_slew_lim_state_is_valid(BW_NULL, state));
 
 	return state->y_z1;
 }
 
 static inline char bw_slew_lim_coeffs_is_valid(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_slew_lim_coeffs"))
@@ -843,13 +848,13 @@ static inline char bw_slew_lim_coeffs_is_valid(
 static inline char bw_slew_lim_state_is_valid(
 		const bw_slew_lim_coeffs * BW_RESTRICT coeffs,
 		const bw_slew_lim_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_slew_lim_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_sr_reduce.h b/include/bw_sr_reduce.h
index e9b0fe2..e066d88 100644
--- a/include/bw_sr_reduce.h
+++ b/include/bw_sr_reduce.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sample rate reducer.
@@ -31,6 +31,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_sr_reduce_set_sample_rate()</code>,
@@ -152,7 +157,7 @@ static inline void bw_sr_reduce_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_sr_reduce_update_coeffs_ctrl()
  *  ```>>> */
@@ -240,8 +245,8 @@ static inline char bw_sr_reduce_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_sr_reduce_state`.
@@ -295,7 +300,7 @@ struct bw_sr_reduce_state {
 
 static inline void bw_sr_reduce_init(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	coeffs->ratio = 1.f;
 
@@ -311,7 +316,7 @@ static inline void bw_sr_reduce_init(
 static inline void bw_sr_reduce_set_sample_rate(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
 		float                             sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -328,7 +333,7 @@ static inline void bw_sr_reduce_set_sample_rate(
 
 static inline void bw_sr_reduce_reset_coeffs(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_set_sample_rate);
 
@@ -346,10 +351,10 @@ static inline float bw_sr_reduce_reset_state(
 		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
 		bw_sr_reduce_state * BW_RESTRICT        state,
 		float                                   x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	(void)coeffs;
@@ -375,18 +380,18 @@ static inline void bw_sr_reduce_reset_state_multi(
 		const float *                                        x_0,
 		float *                                              y_0,
 		size_t                                               n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_sr_reduce_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -395,12 +400,12 @@ static inline void bw_sr_reduce_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_sr_reduce_update_coeffs_ctrl(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
 
@@ -409,7 +414,7 @@ static inline void bw_sr_reduce_update_coeffs_ctrl(
 
 static inline void bw_sr_reduce_update_coeffs_audio(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
 
@@ -420,10 +425,10 @@ static inline float bw_sr_reduce_process1(
 		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
 		bw_sr_reduce_state * BW_RESTRICT        state,
 		float                                   x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -448,14 +453,14 @@ static inline void bw_sr_reduce_process(
 		const float *                     x,
 		float *                           y,
 		size_t                            n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	for (size_t i = 0; i < n_samples; i++)
 		y[i] = bw_sr_reduce_process1(coeffs, state, x[i]);
@@ -473,17 +478,17 @@ static inline void bw_sr_reduce_process_multi(
 		float * const *                                      y,
 		size_t                                               n_channels,
 		size_t                                               n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -500,7 +505,7 @@ static inline void bw_sr_reduce_process_multi(
 static inline void bw_sr_reduce_set_ratio(
 		bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
 		float                             value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_sr_reduce_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_sr_reduce_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -514,7 +519,7 @@ static inline void bw_sr_reduce_set_ratio(
 
 static inline char bw_sr_reduce_coeffs_is_valid(
 		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_sr_reduce_coeffs"))
@@ -529,13 +534,13 @@ static inline char bw_sr_reduce_coeffs_is_valid(
 static inline char bw_sr_reduce_state_is_valid(
 		const bw_sr_reduce_coeffs * BW_RESTRICT coeffs,
 		const bw_sr_reduce_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_sr_reduce_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_src.h b/include/bw_src.h
index eb4e617..49f53b9 100644
--- a/include/bw_src.h
+++ b/include/bw_src.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Aribtrary-ratio IIR sample rate converter.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_src_reset_state_multi()</code> and updated C++
@@ -130,7 +135,7 @@ static inline void bw_src_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_src_process()
  *  ```>>> */
@@ -200,8 +205,8 @@ static inline char bw_src_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_src_state`.
@@ -257,7 +262,7 @@ struct bw_src_state {
 static inline void bw_src_init(
 		bw_src_coeffs * BW_RESTRICT coeffs,
 		float                       ratio) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT(ratio > 0.f);
 
 	coeffs->k = ratio >= 1.f ? 1.f / ratio : -1.f / ratio;
@@ -283,9 +288,9 @@ static inline float bw_src_reset_state(
 		const bw_src_coeffs * BW_RESTRICT coeffs,
 		bw_src_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	if (coeffs->k < 0) {
@@ -325,17 +330,17 @@ static inline void bw_src_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_src_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -343,7 +348,7 @@ static inline void bw_src_reset_state_multi(
 			bw_src_reset_state(coeffs, state[i], x_0[i]);
 
 	BW_ASSERT_DEEP(bw_src_coeffs_is_valid(coeffs));
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_src_process(
@@ -353,16 +358,16 @@ static inline void bw_src_process(
 		float * BW_RESTRICT               y,
 		size_t * BW_RESTRICT              n_in_samples,
 		size_t * BW_RESTRICT              n_out_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_state_is_valid(coeffs, state));
-	BW_ASSERT(n_in_samples != NULL);
-	BW_ASSERT(n_out_samples != NULL);
+	BW_ASSERT(n_in_samples != BW_NULL);
+	BW_ASSERT(n_out_samples != BW_NULL);
 	BW_ASSERT(n_in_samples != n_out_samples);
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, *n_in_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 	BW_ASSERT(x != y);
 
 	size_t i = 0;
@@ -444,16 +449,16 @@ static inline void bw_src_process_multi(
 		size_t                                         n_channels,
 		size_t * BW_RESTRICT                           n_in_samples,
 		size_t * BW_RESTRICT                           n_out_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 	BW_ASSERT((void *)x != (void *)y);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
@@ -463,8 +468,8 @@ static inline void bw_src_process_multi(
 		for (size_t j = 0; j < n_channels; j++)
 			BW_ASSERT((void *)x[i] != (void *)y[j]);
 #endif
-	BW_ASSERT(n_in_samples != NULL);
-	BW_ASSERT(n_out_samples != NULL);
+	BW_ASSERT(n_in_samples != BW_NULL);
+	BW_ASSERT(n_out_samples != BW_NULL);
 	BW_ASSERT(n_in_samples != n_out_samples);
 
 	for (size_t i = 0; i < n_channels; i++)
@@ -475,7 +480,7 @@ static inline void bw_src_process_multi(
 
 static inline char bw_src_coeffs_is_valid(
 		const bw_src_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_src_coeffs"))
@@ -493,13 +498,13 @@ static inline char bw_src_coeffs_is_valid(
 static inline char bw_src_state_is_valid(
 		const bw_src_coeffs * BW_RESTRICT coeffs,
 		const bw_src_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_src_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_src_int.h b/include/bw_src_int.h
index 905ae5b..580a3cd 100644
--- a/include/bw_src_int.h
+++ b/include/bw_src_int.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Integer-ratio IIR sample rate converter.
@@ -33,6 +33,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added <code>bw_src_int_reset_state_multi()</code> and updated
@@ -139,7 +144,7 @@ static inline void bw_src_int_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_src_int_process()
  *  ```>>> */
@@ -184,7 +189,7 @@ static inline void bw_src_int_process_multi(
  *    A given buffer cannot be used both as an input and output buffer.
  *
  *    `n_out_samples` is filled with the number of generated output samples for
- *    each output buffer, if not `NULL`.
+ *    each output buffer, if not `BW_NULL`.
  *
  *    #### bw_src_int_coeffs_is_valid()
  *  ```>>> */
@@ -208,8 +213,8 @@ static inline char bw_src_int_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_src_int_state`.
@@ -262,7 +267,7 @@ struct bw_src_int_state {
 static inline void bw_src_int_init(
 		bw_src_int_coeffs * BW_RESTRICT coeffs,
 		int ratio) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT(ratio < -1 || ratio > 1);
 
 	coeffs->ratio = ratio;
@@ -288,9 +293,9 @@ static inline float bw_src_int_reset_state(
 		const bw_src_int_coeffs * BW_RESTRICT coeffs,
 		bw_src_int_state * BW_RESTRICT        state,
 		float                                 x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_int_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	if (coeffs->ratio < 0) {
@@ -327,17 +332,17 @@ static inline void bw_src_int_reset_state_multi(
 		const float *                                      x_0,
 		float *                                            y_0,
 		size_t                                             n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_int_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_src_int_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -345,7 +350,7 @@ static inline void bw_src_int_reset_state_multi(
 			bw_src_int_reset_state(coeffs, state[i], x_0[i]);
 
 	BW_ASSERT_DEEP(bw_src_int_coeffs_is_valid(coeffs));
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline size_t bw_src_int_process(
@@ -354,13 +359,13 @@ static inline size_t bw_src_int_process(
 		const float * BW_RESTRICT             x,
 		float * BW_RESTRICT                   y,
 		size_t                                n_in_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_int_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_int_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_in_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 	BW_ASSERT(x != y);
 
 	size_t n = 0;
@@ -420,16 +425,16 @@ static inline void bw_src_int_process_multi(
 		size_t                                             n_channels,
 		size_t                                             n_in_samples,
 		size_t * BW_RESTRICT                               n_out_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_src_int_coeffs_is_valid(coeffs));
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 	BW_ASSERT((void *)x != (void *)y);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
@@ -440,7 +445,7 @@ static inline void bw_src_int_process_multi(
 			BW_ASSERT((void *)x[i] != (void *)y[j]);
 #endif
 
-	if (n_out_samples != NULL)
+	if (n_out_samples != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			n_out_samples[i] = bw_src_int_process(coeffs, state[i], x[i], y[i], n_in_samples);
 	else
@@ -452,7 +457,7 @@ static inline void bw_src_int_process_multi(
 
 static inline char bw_src_int_coeffs_is_valid(
 		const bw_src_int_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_src_int_coeffs"))
@@ -470,13 +475,13 @@ static inline char bw_src_int_coeffs_is_valid(
 static inline char bw_src_int_state_is_valid(
 		const bw_src_int_coeffs * BW_RESTRICT coeffs,
 		const bw_src_int_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_src_int_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_svf.h b/include/bw_svf.h
index 8135511..0324939 100644
--- a/include/bw_svf.h
+++ b/include/bw_svf.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    State variable filter (2nd order, 12 dB/oct) model with separated lowpass,
@@ -28,6 +28,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Changed model to get positive polarity at the bandpass
@@ -174,7 +179,7 @@ static inline void bw_svf_reset_state_multi(
  *
  *    The corresponding initial lowpass, bandpass, and highpass output values
  *    are put into the `y_lp_0`, `y_bp_0`, and `y_hp_0` arrays, respectively, if
- *    they are not `NULL`.
+ *    they are not `BW_NULL`.
  *
  *    #### bw_svf_update_coeffs_ctrl()
  *  ```>>> */
@@ -217,8 +222,8 @@ static inline void bw_svf_process(
 /*! <<<```
  *    Processes the first `n_samples` of the input buffer `x` and fills the
  *    first `n_samples` of the output buffers `y_lp` (lowpass), `y_bp`
- *    (bandpass), and `y_hp` (highpass), if they are not `NULL`, while using and
- *    updating both `coeffs` and `state` (control and audio rate).
+ *    (bandpass), and `y_hp` (highpass), if they are not `BW_NULL`, while using
+ *    and updating both `coeffs` and `state` (control and audio rate).
  * 
  *    #### bw_svf_process_multi()
  *  ```>>> */
@@ -238,7 +243,7 @@ static inline void bw_svf_process_multi(
  *    updating both the common `coeffs` and each of the `n_channels` `state`s
  *    (control and audio rate).
  * 
- *    `y_lp`, `y_bp`, and `y_hp`, or any of their elements may be `NULL`.
+ *    `y_lp`, `y_bp`, and `y_hp`, or any of their elements may be `BW_NULL`.
  *
  *    #### bw_svf_set_cutoff()
  *  ```>>> */
@@ -312,8 +317,8 @@ static inline char bw_svf_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_svf_state`.
@@ -390,7 +395,7 @@ struct bw_svf_state {
 
 static inline void bw_svf_init(
 		bw_svf_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_one_pole_init(&coeffs->smooth_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.005f);
@@ -412,7 +417,7 @@ static inline void bw_svf_init(
 static inline void bw_svf_set_sample_rate(
 		bw_svf_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -462,7 +467,7 @@ static inline void bw_svf_do_update_coeffs(
 
 static inline void bw_svf_reset_coeffs(
 		bw_svf_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_set_sample_rate);
 
@@ -486,14 +491,14 @@ static inline void bw_svf_reset_state(
 		float * BW_RESTRICT               y_lp_0,
 		float * BW_RESTRICT               y_bp_0,
 		float * BW_RESTRICT               y_hp_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
-	BW_ASSERT(y_lp_0 != NULL);
-	BW_ASSERT(y_bp_0 != NULL);
-	BW_ASSERT(y_hp_0 != NULL);
+	BW_ASSERT(y_lp_0 != BW_NULL);
+	BW_ASSERT(y_bp_0 != BW_NULL);
+	BW_ASSERT(y_hp_0 != BW_NULL);
 	BW_ASSERT(y_lp_0 != y_bp_0);
 	BW_ASSERT(y_lp_0 != y_hp_0);
 	BW_ASSERT(y_bp_0 != y_hp_0);
@@ -526,20 +531,20 @@ static inline void bw_svf_reset_state_multi(
 		float *                                        y_bp_0,
 		float *                                        y_hp_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_lp_0 != NULL) {
-		if (y_bp_0 != NULL) {
-			if (y_hp_0 != NULL) {
+	if (y_lp_0 != BW_NULL) {
+		if (y_bp_0 != BW_NULL) {
+			if (y_hp_0 != BW_NULL) {
 				for (size_t i = 0; i < n_channels; i++)
 					bw_svf_reset_state(coeffs, state[i], x_0[i], y_lp_0 + i, y_bp_0 + i, y_hp_0 + i);
 			} else {
@@ -549,7 +554,7 @@ static inline void bw_svf_reset_state_multi(
 				}
 			}
 		} else {
-			if (y_hp_0 != NULL) {
+			if (y_hp_0 != BW_NULL) {
 				for (size_t i = 0; i < n_channels; i++) {
 					float v_bp;
 					bw_svf_reset_state(coeffs, state[i], x_0[i], y_lp_0 + i, &v_bp, y_hp_0 + i);
@@ -562,8 +567,8 @@ static inline void bw_svf_reset_state_multi(
 			}
 		}
 	} else {
-		if (y_bp_0 != NULL) {
-			if (y_hp_0 != NULL) {
+		if (y_bp_0 != BW_NULL) {
+			if (y_hp_0 != BW_NULL) {
 				for (size_t i = 0; i < n_channels; i++) {
 					float v_lp;
 					bw_svf_reset_state(coeffs, state[i], x_0[i], &v_lp, y_bp_0 + i, y_hp_0 + i);
@@ -575,7 +580,7 @@ static inline void bw_svf_reset_state_multi(
 				}
 			}
 		} else {
-			if (y_hp_0 != NULL) {
+			if (y_hp_0 != BW_NULL) {
 				for (size_t i = 0; i < n_channels; i++) {
 					float v_lp, v_bp;
 					bw_svf_reset_state(coeffs, state[i], x_0[i], &v_lp, &v_bp, y_hp_0 + i);
@@ -591,14 +596,14 @@ static inline void bw_svf_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_lp_0 != NULL ? bw_has_only_finite(y_lp_0, n_channels) : 1);
-	BW_ASSERT_DEEP(y_bp_0 != NULL ? bw_has_only_finite(y_bp_0, n_channels) : 1);
-	BW_ASSERT_DEEP(y_hp_0 != NULL ? bw_has_only_finite(y_hp_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_lp_0 != BW_NULL ? bw_has_only_finite(y_lp_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_bp_0 != BW_NULL ? bw_has_only_finite(y_bp_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_hp_0 != BW_NULL ? bw_has_only_finite(y_hp_0, n_channels) : 1);
 }
 
 static inline void bw_svf_update_coeffs_ctrl(
 		bw_svf_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
 
@@ -607,7 +612,7 @@ static inline void bw_svf_update_coeffs_ctrl(
 
 static inline void bw_svf_update_coeffs_audio(
 		bw_svf_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
 
@@ -624,15 +629,15 @@ static inline void bw_svf_process1(
 		float * BW_RESTRICT               y_lp,
 		float * BW_RESTRICT               y_bp,
 		float * BW_RESTRICT               y_hp) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
-	BW_ASSERT(y_lp != NULL);
-	BW_ASSERT(y_bp != NULL);
-	BW_ASSERT(y_hp != NULL);
+	BW_ASSERT(y_lp != BW_NULL);
+	BW_ASSERT(y_bp != BW_NULL);
+	BW_ASSERT(y_hp != BW_NULL);
 	BW_ASSERT(y_lp != y_bp);
 	BW_ASSERT(y_lp != y_hp);
 	BW_ASSERT(y_bp != y_hp);
@@ -664,20 +669,20 @@ static inline void bw_svf_process(
 		float *                     y_bp,
 		float *                     y_hp,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y_lp == NULL || y_bp == NULL || y_lp != y_bp);
-	BW_ASSERT(y_lp == NULL || y_hp == NULL || y_lp != y_hp);
-	BW_ASSERT(y_bp == NULL || y_hp == NULL || y_bp != y_hp);
+	BW_ASSERT(y_lp == BW_NULL || y_bp == BW_NULL || y_lp != y_bp);
+	BW_ASSERT(y_lp == BW_NULL || y_hp == BW_NULL || y_lp != y_hp);
+	BW_ASSERT(y_bp == BW_NULL || y_hp == BW_NULL || y_bp != y_hp);
 
-	if (y_lp != NULL) {
-		if (y_bp != NULL) {
-			if (y_hp != NULL) {
+	if (y_lp != BW_NULL) {
+		if (y_bp != BW_NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					bw_svf_process1(coeffs, state, x[i], y_lp + i, y_bp + i, y_hp + i);
@@ -690,7 +695,7 @@ static inline void bw_svf_process(
 				}
 			}
 		} else {
-			if (y_hp != NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					float v_bp;
@@ -705,8 +710,8 @@ static inline void bw_svf_process(
 			}
 		}
 	} else {
-		if (y_bp != NULL) {
-			if (y_hp != NULL) {
+		if (y_bp != BW_NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					float v_lp;
@@ -720,7 +725,7 @@ static inline void bw_svf_process(
 				}
 			}
 		} else {
-			if (y_hp != NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					float v_lp, v_bp;
@@ -739,9 +744,9 @@ static inline void bw_svf_process(
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_svf_state_is_valid(coeffs, state));
-	BW_ASSERT_DEEP(y_lp != NULL ? bw_has_only_finite(y_lp, n_samples) : 1);
-	BW_ASSERT_DEEP(y_bp != NULL ? bw_has_only_finite(y_bp, n_samples) : 1);
-	BW_ASSERT_DEEP(y_hp != NULL ? bw_has_only_finite(y_hp, n_samples) : 1);
+	BW_ASSERT_DEEP(y_lp != BW_NULL ? bw_has_only_finite(y_lp, n_samples) : 1);
+	BW_ASSERT_DEEP(y_bp != BW_NULL ? bw_has_only_finite(y_bp, n_samples) : 1);
+	BW_ASSERT_DEEP(y_hp != BW_NULL ? bw_has_only_finite(y_hp, n_samples) : 1);
 }
 
 static inline void bw_svf_process_multi(
@@ -753,49 +758,49 @@ static inline void bw_svf_process_multi(
 		float * const *                                y_hp,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y_lp == NULL || y_bp == NULL || y_lp != y_bp);
-	BW_ASSERT(y_lp == NULL || y_hp == NULL || y_lp != y_hp);
-	BW_ASSERT(y_bp == NULL || y_hp == NULL || y_bp != y_hp);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y_lp == BW_NULL || y_bp == BW_NULL || y_lp != y_bp);
+	BW_ASSERT(y_lp == BW_NULL || y_hp == BW_NULL || y_lp != y_hp);
+	BW_ASSERT(y_bp == BW_NULL || y_hp == BW_NULL || y_bp != y_hp);
 #ifndef BW_NO_DEBUG
-	if (y_lp != NULL)
+	if (y_lp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] == NULL || y_lp[j] == NULL || y_lp[i] != y_lp[j]);
-	if (y_bp != NULL)
+				BW_ASSERT(y_lp[i] == BW_NULL || y_lp[j] == BW_NULL || y_lp[i] != y_lp[j]);
+	if (y_bp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_bp[i] == NULL || y_bp[j] == NULL || y_bp[i] != y_bp[j]);
-	if (y_hp != NULL)
+				BW_ASSERT(y_bp[i] == BW_NULL || y_bp[j] == BW_NULL || y_bp[i] != y_bp[j]);
+	if (y_hp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_hp[i] == NULL || y_hp[j] == NULL || y_hp[i] != y_hp[j]);
-	if (y_lp != NULL && y_bp != NULL)
+				BW_ASSERT(y_hp[i] == BW_NULL || y_hp[j] == BW_NULL || y_hp[i] != y_hp[j]);
+	if (y_lp != BW_NULL && y_bp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] == NULL || y_bp[j] == NULL || y_lp[i] != y_bp[j]);
-	if (y_lp != NULL && y_hp != NULL)
+				BW_ASSERT(y_lp[i] == BW_NULL || y_bp[j] == BW_NULL || y_lp[i] != y_bp[j]);
+	if (y_lp != BW_NULL && y_hp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] == NULL || y_hp[j] == NULL || y_lp[i] != y_hp[j]);
-	if (y_bp != NULL && y_hp != NULL)
+				BW_ASSERT(y_lp[i] == BW_NULL || y_hp[j] == BW_NULL || y_lp[i] != y_hp[j]);
+	if (y_bp != BW_NULL && y_hp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_bp[i] == NULL || y_hp[j] == NULL || y_bp[i] != y_hp[j]);
+				BW_ASSERT(y_bp[i] == BW_NULL || y_hp[j] == BW_NULL || y_bp[i] != y_hp[j]);
 #endif
 
-	if (y_lp != NULL) {
-		if (y_bp != NULL) {
-			if (y_hp != NULL) {
+	if (y_lp != BW_NULL) {
+		if (y_bp != BW_NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -823,7 +828,7 @@ static inline void bw_svf_process_multi(
 				}
 			}
 		} else {
-			if (y_hp != NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -848,8 +853,8 @@ static inline void bw_svf_process_multi(
 			}
 		}
 	} else {
-		if (y_bp != NULL) {
-			if (y_hp != NULL) {
+		if (y_bp != BW_NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -873,7 +878,7 @@ static inline void bw_svf_process_multi(
 				}
 			}
 		} else {
-			if (y_hp != NULL) {
+			if (y_hp != BW_NULL) {
 				for (size_t i = 0; i < n_samples; i++) {
 					bw_svf_update_coeffs_audio(coeffs);
 					for (size_t j = 0; j < n_channels; j++) {
@@ -902,7 +907,7 @@ static inline void bw_svf_process_multi(
 static inline void bw_svf_set_cutoff(
 		bw_svf_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -917,7 +922,7 @@ static inline void bw_svf_set_cutoff(
 static inline void bw_svf_set_Q(
 		bw_svf_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -932,7 +937,7 @@ static inline void bw_svf_set_Q(
 static inline void bw_svf_set_prewarp_at_cutoff(
 		bw_svf_coeffs * BW_RESTRICT coeffs,
 		char                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_init);
 
@@ -945,7 +950,7 @@ static inline void bw_svf_set_prewarp_at_cutoff(
 static inline void bw_svf_set_prewarp_freq(
 		bw_svf_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_svf_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_svf_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -959,7 +964,7 @@ static inline void bw_svf_set_prewarp_freq(
 
 static inline char bw_svf_coeffs_is_valid(
 		const bw_svf_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_svf_coeffs"))
@@ -1017,13 +1022,13 @@ static inline char bw_svf_coeffs_is_valid(
 static inline char bw_svf_state_is_valid(
 		const bw_svf_coeffs * BW_RESTRICT coeffs,
 		const bw_svf_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_svf_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
diff --git a/include/bw_trem.h b/include/bw_trem.h
index ef61fc2..39b7dd9 100644
--- a/include/bw_trem.h
+++ b/include/bw_trem.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{
  *    bw_common bw_math bw_one_pole bw_osc_sin bw_phase_gen bw_ring_mod
  *  }}}
@@ -29,6 +29,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input value to
@@ -142,7 +147,7 @@ static inline void bw_trem_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_trem_update_coeffs_ctrl()
  *  ```>>> */
@@ -244,8 +249,8 @@ static inline char bw_trem_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_trem_state`.
@@ -301,7 +306,7 @@ struct bw_trem_state {
 
 static inline void bw_trem_init(
 		bw_trem_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_phase_gen_init(&coeffs->phase_gen_coeffs);
 	bw_ring_mod_init(&coeffs->ring_mod_coeffs);
@@ -318,7 +323,7 @@ static inline void bw_trem_init(
 static inline void bw_trem_set_sample_rate(
 		bw_trem_coeffs * BW_RESTRICT coeffs,
 		float                        sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -335,7 +340,7 @@ static inline void bw_trem_set_sample_rate(
 
 static inline void bw_trem_reset_coeffs(
 		bw_trem_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_set_sample_rate);
 
@@ -354,10 +359,10 @@ static inline float bw_trem_reset_state(
 		const bw_trem_coeffs * BW_RESTRICT coeffs,
 		bw_trem_state * BW_RESTRICT        state,
 		float                              x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float p, pi;
@@ -383,18 +388,18 @@ static inline void bw_trem_reset_state_multi(
 		const float *                                   x_0,
 		float *                                         y_0,
 		size_t                                          n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_trem_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -403,12 +408,12 @@ static inline void bw_trem_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_trem_update_coeffs_ctrl(
 		bw_trem_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
 
@@ -421,7 +426,7 @@ static inline void bw_trem_update_coeffs_ctrl(
 
 static inline void bw_trem_update_coeffs_audio(
 		bw_trem_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
 
@@ -436,10 +441,10 @@ static inline float bw_trem_process1(
 		const bw_trem_coeffs * BW_RESTRICT coeffs,
 		bw_trem_state * BW_RESTRICT        state,
 		float                              x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -462,14 +467,14 @@ static inline void bw_trem_process(
 		const float *                x,
 		float *                      y,
 		size_t                       n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_trem_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -490,17 +495,17 @@ static inline void bw_trem_process_multi(
 		float * const *                                 y,
 		size_t                                          n_channels,
 		size_t                                          n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -521,7 +526,7 @@ static inline void bw_trem_process_multi(
 static inline void bw_trem_set_rate(
 		bw_trem_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -535,7 +540,7 @@ static inline void bw_trem_set_rate(
 static inline void bw_trem_set_amount(
 		bw_trem_coeffs * BW_RESTRICT coeffs,
 		float                        value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_trem_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_trem_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -549,7 +554,7 @@ static inline void bw_trem_set_amount(
 
 static inline char bw_trem_coeffs_is_valid(
 		const bw_trem_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_trem_coeffs"))
@@ -564,17 +569,17 @@ static inline char bw_trem_coeffs_is_valid(
 static inline char bw_trem_state_is_valid(
 		const bw_trem_coeffs * BW_RESTRICT coeffs,
 		const bw_trem_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_trem_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_phase_gen_state_is_valid(coeffs ? &coeffs->phase_gen_coeffs : NULL, &state->phase_gen_state);
+	return bw_phase_gen_state_is_valid(coeffs ? &coeffs->phase_gen_coeffs : BW_NULL, &state->phase_gen_state);
 }
 
 #ifdef __cplusplus
diff --git a/include/bw_voice_alloc.h b/include/bw_voice_alloc.h
index 4c39479..ddd1d90 100644
--- a/include/bw_voice_alloc.h
+++ b/include/bw_voice_alloc.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2023 Orastron Srl unipersonale
+ * Copyright (C) 2023, 2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,13 +20,18 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_note_queue }}}
  *  description {{{
  *    Basic voice allocator with low/high note priority.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Specified that velocity can be negative in
@@ -149,15 +154,15 @@ void bw_voice_alloc(
 		bw_note_queue * BW_RESTRICT             queue,
 		void * BW_RESTRICT const * BW_RESTRICT  voices,
 		size_t                                  n_voices) {
-	BW_ASSERT(opts != NULL);
+	BW_ASSERT(opts != BW_NULL);
 	BW_ASSERT(opts->priority == bw_voice_alloc_priority_low || opts->priority == bw_voice_alloc_priority_high);
-	BW_ASSERT(n_voices == 0 || opts->note_on != NULL);
-	BW_ASSERT(n_voices == 0 || opts->note_off != NULL);
-	BW_ASSERT(n_voices == 0 || opts->get_note != NULL);
-	BW_ASSERT(n_voices == 0 || opts->is_free != NULL);
-	BW_ASSERT(queue != NULL);
+	BW_ASSERT(n_voices == 0 || opts->note_on != BW_NULL);
+	BW_ASSERT(n_voices == 0 || opts->note_off != BW_NULL);
+	BW_ASSERT(n_voices == 0 || opts->get_note != BW_NULL);
+	BW_ASSERT(n_voices == 0 || opts->is_free != BW_NULL);
+	BW_ASSERT(queue != BW_NULL);
 	BW_ASSERT_DEEP(bw_note_queue_is_valid(queue));
-	BW_ASSERT(n_voices == 0 || voices != NULL);
+	BW_ASSERT(n_voices == 0 || voices != BW_NULL);
 
 	for (unsigned char i = 0; i < queue->n_events; i++) {
 		bw_note_queue_event *ev = queue->events + i;
diff --git a/include/bw_wah.h b/include/bw_wah.h
index 04b316b..d14e8be 100644
--- a/include/bw_wah.h
+++ b/include/bw_wah.h
@@ -1,7 +1,7 @@
 /*
  * Brickworks
  *
- * Copyright (C) 2022, 2023 Orastron Srl unipersonale
+ * Copyright (C) 2022-2024 Orastron Srl unipersonale
  *
  * Brickworks is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Wah effect.
@@ -29,6 +29,11 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Now using <code>BW_NULL</code>.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>Added initial input value to
@@ -156,7 +161,7 @@ static inline void bw_wah_reset_state_multi(
  *    array.
  *
  *    The corresponding initial output values are written into the `y_0` array,
- *    if not `NULL`.
+ *    if not `BW_NULL`.
  *
  *    #### bw_wah_update_coeffs_ctrl()
  *  ```>>> */
@@ -244,8 +249,8 @@ static inline char bw_wah_state_is_valid(
  *    seems to be the case and `0` if it is certainly not. False positives are
  *    possible, false negatives are not.
  *
- *    If `coeffs` is not `NULL` extra cross-checks might be performed (`state`
- *    is supposed to be associated to `coeffs`).
+ *    If `coeffs` is not `BW_NULL` extra cross-checks might be performed
+ *    (`state` is supposed to be associated to `coeffs`).
  *
  *    `state` must at least point to a readable memory block of size greater
  *    than or equal to that of `bw_wah_state`.
@@ -298,7 +303,7 @@ struct bw_wah_state {
 
 static inline void bw_wah_init(
 		bw_wah_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 	bw_svf_init(&coeffs->svf_coeffs);
 	bw_svf_set_cutoff(&coeffs->svf_coeffs, 600.f);
@@ -316,7 +321,7 @@ static inline void bw_wah_init(
 static inline void bw_wah_set_sample_rate(
 		bw_wah_coeffs * BW_RESTRICT coeffs,
 		float                       sample_rate) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
@@ -332,7 +337,7 @@ static inline void bw_wah_set_sample_rate(
 
 static inline void bw_wah_reset_coeffs(
 		bw_wah_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_set_sample_rate);
 
@@ -350,10 +355,10 @@ static inline float bw_wah_reset_state(
 		const bw_wah_coeffs * BW_RESTRICT coeffs,
 		bw_wah_state * BW_RESTRICT        state,
 		float                             x_0) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	float lp, bp, hp;
@@ -377,18 +382,18 @@ static inline void bw_wah_reset_state_multi(
 		const float *                                  x_0,
 		float *                                        y_0,
 		size_t                                         n_channels) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x_0 != NULL);
+	BW_ASSERT(x_0 != BW_NULL);
 
-	if (y_0 != NULL)
+	if (y_0 != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			y_0[i] = bw_wah_reset_state(coeffs, state[i], x_0[i]);
 	else
@@ -397,12 +402,12 @@ static inline void bw_wah_reset_state_multi(
 
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+	BW_ASSERT_DEEP(y_0 != BW_NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
 static inline void bw_wah_update_coeffs_ctrl(
 		bw_wah_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
 
@@ -414,7 +419,7 @@ static inline void bw_wah_update_coeffs_ctrl(
 
 static inline void bw_wah_update_coeffs_audio(
 		bw_wah_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
 
@@ -428,10 +433,10 @@ static inline float bw_wah_process1(
 		const bw_wah_coeffs * BW_RESTRICT coeffs,
 		bw_wah_state * BW_RESTRICT        state,
 		float                             x) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_state_is_valid(coeffs, state));
 	BW_ASSERT(bw_is_finite(x));
 
@@ -452,14 +457,14 @@ static inline void bw_wah_process(
 		const float *               x,
 		float *                     y,
 		size_t                      n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_state_is_valid(coeffs, state));
-	BW_ASSERT(x != NULL);
+	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(y != BW_NULL);
 
 	bw_wah_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -480,17 +485,17 @@ static inline void bw_wah_process_multi(
 		float * const *                                y,
 		size_t                                         n_channels,
 		size_t                                         n_samples) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_reset_coeffs);
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
 #endif
-	BW_ASSERT(x != NULL);
-	BW_ASSERT(y != NULL);
+	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
@@ -511,7 +516,7 @@ static inline void bw_wah_process_multi(
 static inline void bw_wah_set_wah(
 		bw_wah_coeffs * BW_RESTRICT coeffs,
 		float                       value) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 	BW_ASSERT_DEEP(bw_wah_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_wah_coeffs_state_init);
 	BW_ASSERT(bw_is_finite(value));
@@ -525,7 +530,7 @@ static inline void bw_wah_set_wah(
 
 static inline char bw_wah_coeffs_is_valid(
 		const bw_wah_coeffs * BW_RESTRICT coeffs) {
-	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(coeffs != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (coeffs->hash != bw_hash_sdbm("bw_wah_coeffs"))
@@ -540,17 +545,17 @@ static inline char bw_wah_coeffs_is_valid(
 static inline char bw_wah_state_is_valid(
 		const bw_wah_coeffs * BW_RESTRICT coeffs,
 		const bw_wah_state * BW_RESTRICT  state) {
-	BW_ASSERT(state != NULL);
+	BW_ASSERT(state != BW_NULL);
 
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_wah_state"))
 		return 0;
 
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (coeffs != BW_NULL && coeffs->reset_id != state->coeffs_reset_id)
 		return 0;
 #endif
 
-	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : NULL, &state->svf_state);
+	return bw_svf_state_is_valid(coeffs ? &coeffs->svf_coeffs : BW_NULL, &state->svf_state);
 }
 
 #ifdef __cplusplus