From 69b74c4ccbf95bc1b492e9ce9c773b63444048ab Mon Sep 17 00:00:00 2001
From: Stefano D'Angelo <stefano.dangelo@orastron.com>
Date: Fri, 15 Sep 2023 08:30:01 +0200
Subject: [PATCH] finalized bw_env_follow, untested + wip bw_comp

---
 include/bw_comp.h       | 214 +++++++++++++++---
 include/bw_env_follow.h | 475 +++++++++++++++++++++++++++++++++++-----
 2 files changed, 601 insertions(+), 88 deletions(-)

diff --git a/include/bw_comp.h b/include/bw_comp.h
index 193eb55..84c17d1 100644
--- a/include/bw_comp.h
+++ b/include/bw_comp.h
@@ -31,8 +31,10 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
- *          <li>Added initial value arguments in
- *              <code>bw_comp_reset_state()</code>.</li>
+ *          <li>Added <code>bw_comp_reset_state_multi()</code> and updated C++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_comp_reset_state()</code> returns the initial
+ *              output value.</li>
  *          <li>Added overloaded C++ <code>reset()</code> functions taking
  *              arrays as arguments.</li>
  *          <li><code>bw_comp_process()</code> and
@@ -44,6 +46,8 @@
  *          <li>Added overloaded C++ <code>process()</code> function taking
  *              C-style arrays as arguments.</li>
  *          <li>Removed usage of reserved identifiers.</li>
+ *          <li>Clearly specified parameter validity ranges.</li>
+ *          <li>Added debugging code.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>0.6.0</strong>:
@@ -92,45 +96,77 @@ typedef struct bw_comp_state bw_comp_state;
  *
  *    #### bw_comp_init()
  *  ```>>> */
-static inline void bw_comp_init(bw_comp_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comp_init(
+	bw_comp_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
  *    #### bw_comp_set_sample_rate()
  *  ```>>> */
-static inline void bw_comp_set_sample_rate(bw_comp_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_comp_set_sample_rate(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_comp_reset_coeffs()
  *  ```>>> */
-static inline void bw_comp_reset_coeffs(bw_comp_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comp_reset_coeffs(
+	bw_comp_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_comp_reset_state()
  *  ```>>> */
-static inline void bw_comp_reset_state(const bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, float x_0, float x_sc_0);
+static inline float bw_comp_reset_state(
+	const bw_comp_coeffs * BW_RESTRICT coeffs,
+	bw_comp_state * BW_RESTRICT        state,
+	float                              x_0,
+	float                              x_sc_0);
 /*! <<<```
  *    Resets the given `state` to its initial values using the given `coeffs`
- *    and the quiescent/initial input value `x_0` and sidechain input value
- *    `x_sc_0`.
+ *    and the initial input value `x_0` and sidechain input value `x_sc_0`.
+ *
+ *    Returns the corresponding initial output value.
+ *
+ *    #### bw_comp_reset_state_multi()
+ *  ```>>> */
+static inline void bw_comp_reset_state_multi(
+	const bw_comp_coeffs * BW_RESTRICT              coeffs,
+	bw_comp_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float *                                   x_0,
+	const float *                                   x_sc_0,
+	float *                                         y_0,
+	size_t                                          n_channels);
+/*! <<<```
+ *    Resets each of the `n_channels` `state`s to its initial values using the
+ *    given `coeffs` and the corresponding initial input value in the `x_0`
+ *    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`.
  *
  *    #### bw_comp_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_comp_update_coeffs_ctrl(bw_comp_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comp_update_coeffs_ctrl(
+	bw_comp_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_comp_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_comp_update_coeffs_audio(bw_comp_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comp_update_coeffs_audio(
+	bw_comp_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_comp_process1()
  *  ```>>> */
-static inline float bw_comp_process1(const bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, float x, float x_sc);
+static inline float bw_comp_process1(
+	const bw_comp_coeffs * BW_RESTRICT coeffs,
+	bw_comp_state * BW_RESTRICT        state,
+	float                              x,
+	float                              x_sc);
 /*! <<<```
  *    Processes one input sample `x` and the corresponding sidechain input
  *    sample `x_sc` using `coeffs`, while using and updating `state`. Returns
@@ -138,7 +174,13 @@ static inline float bw_comp_process1(const bw_comp_coeffs *BW_RESTRICT coeffs, b
  *
  *    #### bw_comp_process()
  *  ```>>> */
-static inline void bw_comp_process(bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, const float *x, const float *x_sc, float *y, size_t n_samples);
+static inline void bw_comp_process(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	bw_comp_state * BW_RESTRICT  state,
+	const float *                x,
+	const float *                x_sc,
+	float *                      y,
+	size_t                       n_samples);
 /*! <<<```
  *    Processes the first `n_samples` of the input buffer `x` and the first
  *    `n_samples` of the sidechain input buffer `x_sc`, and fills the first
@@ -147,7 +189,14 @@ static inline void bw_comp_process(bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_s
  *
  *    #### bw_comp_process_multi()
  *  ```>>> */
-static inline void bw_comp_process_multi(bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, const float * const *x_sc, float * const *y, size_t n_channels, size_t n_samples);
+static inline void bw_comp_process_multi(
+	bw_comp_coeffs * BW_RESTRICT                    coeffs,
+	bw_comp_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float * const *                           x,
+	const float * const *                           x_sc,
+	float * const *                                 y,
+	size_t                                          n_channels,
+	size_t                                          n_samples);
 /*! <<<```
  *    Processes the first `n_samples` of the `n_channels` input buffers `x` and
  *    the first `n_samples` of the `n_channels` sidechain input buffers `x_sc`,
@@ -157,23 +206,33 @@ static inline void bw_comp_process_multi(bw_comp_coeffs *BW_RESTRICT coeffs, bw_
  *
  *    #### bw_comp_set_thresh_lin()
  *  ```>>> */
-static inline void bw_comp_set_thresh_lin(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_thresh_lin(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the threshold `value` (linear) in `coeffs`.
  *
+ *    Valid range: [`1e-20f`, `1e20f`].
+ *
  *    Default value: `1.f`.
  *
  *    #### bw_comp_set_thresh_dBFS()
  *  ```>>> */
-static inline void bw_comp_set_thresh_dBFS(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_thresh_dBFS(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the threshold `value` (dBFS) in `coeffs`.
  *
+ *    Valid range: [`-400.f`, `400.f`].
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comp_set_ratio()
  *  ```>>> */
-static inline void bw_comp_set_ratio(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_ratio(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the compression ratio `value` in `coeffs`.
  *
@@ -186,34 +245,50 @@ static inline void bw_comp_set_ratio(bw_comp_coeffs *BW_RESTRICT coeffs, float v
  *
  *    #### bw_comp_set_attack_tau()
  *  ```>>> */
-static inline void bw_comp_set_attack_tau(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_attack_tau(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the attack time constant `value` (s) in `coeffs`.
  *
+ *    `value` must be non-negative.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comp_set_release_tau()
  *  ```>>> */
-static inline void bw_comp_set_release_tau(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_release_tau(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the release time constant `value` (s) in `coeffs`.
  *
+ *    `value` must be non-negative.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comp_set_gain_lin()
  *  ```>>> */
-static inline void bw_comp_set_gain_lin(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_gain_lin(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the output makeup gain `value` (linear ratio) in `coeffs`.
  *
+ *    `value` must be finite.
+ *
  *    Default value: `1.f`.
  *
  *    #### bw_comp_set_gain_dB()
  *  ```>>> */
-static inline void bw_comp_set_gain_dB(bw_comp_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comp_set_gain_dB(
+	bw_comp_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the output makeup gain `value` (dB) in `coeffs`.
  *
+ *    `value` must be less than or equal to `770.630f`.
+ *
  *    Default value: `0.f`.
  *  }}} */
 
@@ -235,49 +310,110 @@ static inline void bw_comp_set_gain_dB(bw_comp_coeffs *BW_RESTRICT coeffs, float
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_comp_coeffs_state {
+	bw_comp_coeffs_state_invalid,
+	bw_comp_coeffs_state_init,
+	bw_comp_coeffs_state_set_sample_rate,
+	bw_comp_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_comp_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_comp_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_env_follow_coeffs	env_follow_coeffs;
-	bw_gain_coeffs		gain_coeffs;
-	bw_one_pole_coeffs	smooth_coeffs;
-	bw_one_pole_state	smooth_thresh_state;
-	bw_one_pole_state	smooth_ratio_state;
+	bw_env_follow_coeffs		env_follow_coeffs;
+	bw_gain_coeffs			gain_coeffs;
+	bw_one_pole_coeffs		smooth_coeffs;
+	bw_one_pole_state		smooth_thresh_state;
+	bw_one_pole_state		smooth_ratio_state;
 	
 	// Coefficients
-	float			kc;
+	float				kc;
 
 	// Parameters
-	float			thresh;
-	float			ratio;
+	float				thresh;
+	float				ratio;
 };
 
 struct bw_comp_state {
+#ifdef BW_DEBUG_DEEP
+	uint32_t		hash;
+	uint32_t		coeffs_reset_id;
+#endif
+
+	// Sub-components
 	bw_env_follow_state	env_follow_state;
 };
 
-static inline void bw_comp_init(bw_comp_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_comp_init(
+		bw_comp_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	bw_env_follow_init(&coeffs->env_follow_coeffs);
 	bw_gain_init(&coeffs->gain_coeffs);
 	bw_one_pole_set_tau(&coeffs->smooth_coeffs, 0.05f);
 	coeffs->thresh = 1.f;
 	coeffs->ratio = 1.f;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_comp_coeffs");
+	coeffs->state = bw_comp_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comp_coeffs_state_init);
 }
 
-static inline void bw_comp_set_sample_rate(bw_comp_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+static inline void bw_comp_set_sample_rate(
+		bw_comp_coeffs * BW_RESTRICT coeffs,
+		float                        sample_rate) {
+	BW_ASSERT(coeffs != 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);
+
 	bw_env_follow_set_sample_rate(&coeffs->env_follow_coeffs, sample_rate);
 	bw_gain_set_sample_rate(&coeffs->gain_coeffs, sample_rate);
 	bw_one_pole_set_sample_rate(&coeffs->smooth_coeffs, sample_rate);
 	bw_one_pole_reset_coeffs(&coeffs->smooth_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_comp_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comp_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_comp_reset_coeffs(bw_comp_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_comp_reset_coeffs(
+		bw_comp_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comp_coeffs_state_set_sample_rate);
+
 	bw_env_follow_reset_coeffs(&coeffs->env_follow_coeffs);
 	bw_gain_reset_coeffs(&coeffs->gain_coeffs);
 	bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_thresh_state, coeffs->thresh);
 	bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_ratio_state, coeffs->ratio);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_comp_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_comp_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comp_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_comp_reset_state(const bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, float x_0, float x_sc_0) {
+static inline float bw_comp_reset_state(
+		const bw_comp_coeffs * BW_RESTRICT coeffs,
+		bw_comp_state * BW_RESTRICT state,
+		float x_0,
+		float x_sc_0) {
 	(void)x_0;
 	bw_env_follow_reset_state(&coeffs->env_follow_coeffs, &state->env_follow_state, x_sc_0);
 }
@@ -297,8 +433,18 @@ static inline void bw_comp_update_coeffs_audio(bw_comp_coeffs *BW_RESTRICT coeff
 static inline float bw_comp_process1(const bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, float x, float x_sc) {
 	const float env = bw_env_follow_process1(&coeffs->env_follow_coeffs, &state->env_follow_state, x_sc);
 	const float thresh = bw_one_pole_get_y_z1(&coeffs->smooth_thresh_state);
-	const float y = env > thresh ? bw_pow2f(coeffs->kc * bw_log2f(thresh * bw_rcpf(env))) * x : x;
-	return bw_gain_process1(&coeffs->gain_coeffs, y);
+	float y;
+	if (env > thresh) {
+		float v = thresh * bw_rcpf(env);
+		if (v >= 1.175494350822287e-38f) {
+			v = coeffs->kc * bw_log2f(v);
+			y = v > -126.f ? bw_pow2f(v) * x: thresh;
+		} else
+			y = thresh;
+	} else
+		y = x;
+	y = bw_gain_process1(&coeffs->gain_coeffs, y);
+	return y;
 }
 
 static inline void bw_comp_process(bw_comp_coeffs *BW_RESTRICT coeffs, bw_comp_state *BW_RESTRICT state, const float *x, const float *x_sc, float *y, size_t n_samples) {
diff --git a/include/bw_env_follow.h b/include/bw_env_follow.h
index 027a8eb..af8ce10 100644
--- a/include/bw_env_follow.h
+++ b/include/bw_env_follow.h
@@ -30,6 +30,12 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
+ *          <li>Added <code>bw_env_follow_reset_state_multi()</code> and updated
+ *              C++ API in this regard.</li>
+ *          <li>Now <code>bw_env_follow_reset_state()</code> returns the initial
+ *              output value.</li>
+ *          <li>Added overloaded C++ <code>reset()</code> functions taking
+ *              arrays as arguments.</li>
  *          <li><code>bw_env_follow_process()</code> and
  *              <code>bw_env_follow_process_multi()</code> now use
  *              <code>size_t</code> to count samples and channels.</li>
@@ -39,6 +45,8 @@
  *          <li>Added overloaded C++ <code>process()</code> function taking
  *              C-style arrays as arguments.</li>
  *          <li>Removed usage of reserved identifiers.</li>
+ *          <li>Clearly specified parameter validity ranges.</li>
+ *          <li>Added debugging code.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>0.6.0</strong>:
@@ -95,50 +103,86 @@ typedef struct bw_env_follow_state bw_env_follow_state;
  *
  *    #### bw_env_follow_init()
  *  ```>>> */
-static inline void bw_env_follow_init(bw_env_follow_coeffs *BW_RESTRICT coeffs);
+static inline void bw_env_follow_init(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
  *    #### bw_env_follow_set_sample_rate()
  *  ```>>> */
-static inline void bw_env_follow_set_sample_rate(bw_env_follow_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_env_follow_set_sample_rate(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs,
+	float                              sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_env_follow_reset_coeffs()
  *  ```>>> */
-static inline void bw_env_follow_reset_coeffs(bw_env_follow_coeffs *BW_RESTRICT coeffs);
+static inline void bw_env_follow_reset_coeffs(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_env_follow_reset_state()
  *  ```>>> */
-static inline void bw_env_follow_reset_state(const bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state);
+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);
 /*! <<<```
- *    Resets the given `state` to its initial values using the given `coeffs`.
+ *    Resets the given `state` to its initial values using the given `coeffs`
+ *    and the initial input value `x_0`.
+ *
+ *    Returns the corresponding initial output value.
+ *
+ *    #### bw_env_follow_reset_state_multi()
+ *  ```>>> */
+static inline void bw_env_follow_reset_state_multi(
+	const bw_env_follow_coeffs * BW_RESTRICT              coeffs,
+	bw_env_follow_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float *                                         x_0,
+	float *                                               y_0,
+	size_t                                                n_channels);
+/*! <<<```
+ *    Resets each of the `n_channels` `state`s to its initial values using the
+ *    given `coeffs` and the corresponding initial input value in the `x_0`
+ *    array.
+ *
+ *    The corresponding initial output values are written into the `y_0` array,
+ *    if not `NULL`.
  *
  *    #### bw_env_follow_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_env_follow_update_coeffs_ctrl(bw_env_follow_coeffs *BW_RESTRICT coeffs);
+static inline void bw_env_follow_update_coeffs_ctrl(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_env_follow_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_env_follow_update_coeffs_audio(bw_env_follow_coeffs *BW_RESTRICT coeffs);
+static inline void bw_env_follow_update_coeffs_audio(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_env_follow_process1()
  *  ```>>> */
-static inline float bw_env_follow_process1(const bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state, float x);
+static inline float bw_env_follow_process1(
+	const bw_env_follow_coeffs * BW_RESTRICT coeffs,
+	bw_env_follow_state * BW_RESTRICT        state,
+	float                                    x);
 /*! <<<```
  *    Processes one input sample `x` using `coeffs`, while using and updating
  *    `state`. Returns the corresponding output sample.
  *
  *    #### bw_env_follow_process()
  *  ```>>> */
-static inline void bw_env_follow_process(bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples);
+static inline void bw_env_follow_process(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs,
+	bw_env_follow_state * BW_RESTRICT  state,
+	const float *                      x,
+	float *                            y,
+	size_t                             n_samples);
 /*! <<<```
  *    Processes the first `n_samples` of the input buffer `x` and fills the
  *    first `n_samples` of the output buffer `y`, while using and updating both
@@ -148,7 +192,13 @@ static inline void bw_env_follow_process(bw_env_follow_coeffs *BW_RESTRICT coeff
  *
  *    #### bw_env_follow_process_multi()
  *  ```>>> */
-static inline void bw_env_follow_process_multi(bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, float * const *y, size_t n_channels, size_t n_samples);
+static inline void bw_env_follow_process_multi(
+	bw_env_follow_coeffs * BW_RESTRICT                    coeffs,
+	bw_env_follow_state * BW_RESTRICT const * BW_RESTRICT state,
+	const float * const *                                 x,
+	float * const *                                       y,
+	size_t                                                n_channels,
+	size_t                                                n_samples);
 /*! <<<```
  *    Processes the first `n_samples` of the `n_channels` input buffers `x` and
  *    fills the first `n_samples` of the `n_channels` output buffers `y`, while
@@ -159,27 +209,64 @@ static inline void bw_env_follow_process_multi(bw_env_follow_coeffs *BW_RESTRICT
  *
  *    #### bw_env_follow_set_attack_tau()
  *  ```>>> */
-static inline void bw_env_follow_set_attack_tau(bw_env_follow_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_env_follow_set_attack_tau(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs,
+	float                              value);
 /*! <<<```
  *    Sets the upgoing (attack) time constant in `coeffs` of the one-pole filter
  *    to `value` (s).
  *
+ *    `value` must be non-negative.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_env_follow_set_release_tau()
  *  ```>>> */
-static inline void bw_env_follow_set_release_tau(bw_env_follow_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_env_follow_set_release_tau(
+	bw_env_follow_coeffs * BW_RESTRICT coeffs,
+	float                              value);
 /*! <<<```
  *    Sets the downgoing (release) time constant in `coeffs` of the one-pole
  *    filter to `value` (s).
  *
+ *    `value` must be non-negative.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_env_follow_get_y_z1()
  *  ```>>> */
-static inline float bw_env_follow_get_y_z1(const bw_env_follow_state *BW_RESTRICT state);
+static inline float bw_env_follow_get_y_z1(
+	const bw_env_follow_state * BW_RESTRICT state);
 /*! <<<```
  *    Returns the last output sample as stored in `state`.
+ *
+ *    #### bw_env_follow_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_env_follow_coeffs_is_valid(
+	const bw_env_follow_coeffs * BW_RESTRICT coeffs);
+/*! <<<```
+ *    Tries to determine whether `coeffs` is valid and returns non-`0` if it
+ *    seems to be the case and `0` if it is certainly not. False positives are
+ *    possible, false negatives are not.
+ *
+ *    `coeffs` must at least point to a readable memory block of size greater
+ *    than or equal to that of `bw_env_follow_coeffs`.
+ *
+ *    #### bw_env_follow_state_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);
+/*! <<<```
+ *    Tries to determine whether `state` is valid and returns non-`0` if it
+ *    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`).
+ *
+ *    `state` must at least point to a readable memory block of size greater
+ *    than or equal to that of `bw_env_follow_state`.
  *  }}} */
  
 #ifdef __cplusplus
@@ -198,45 +285,193 @@ static inline float bw_env_follow_get_y_z1(const bw_env_follow_state *BW_RESTRIC
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_env_follow_coeffs_state {
+	bw_env_follow_coeffs_state_invalid,
+	bw_env_follow_coeffs_state_init,
+	bw_env_follow_coeffs_state_set_sample_rate,
+	bw_env_follow_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_env_follow_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_env_follow_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_one_pole_coeffs	one_pole_coeffs;
+	bw_one_pole_coeffs		one_pole_coeffs;
 };
 
 struct bw_env_follow_state {
+#ifdef BW_DEBUG_DEEP
+	uint32_t		hash;
+	uint32_t		coeffs_reset_id;
+#endif
+
+	// Sub-components
 	bw_one_pole_state	one_pole_state;
 };
 
-static inline void bw_env_follow_init(bw_env_follow_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_env_follow_init(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	bw_one_pole_init(&coeffs->one_pole_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_env_follow_coeffs");
+	coeffs->state = bw_env_follow_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_env_follow_coeffs_state_init);
 }
 
-static inline void bw_env_follow_set_sample_rate(bw_env_follow_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+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_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);
+
 	bw_one_pole_set_sample_rate(&coeffs->one_pole_coeffs, sample_rate);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_env_follow_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_env_follow_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_env_follow_reset_coeffs(bw_env_follow_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_env_follow_reset_coeffs(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_set_sample_rate);
+
 	bw_one_pole_reset_coeffs(&coeffs->one_pole_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_env_follow_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_env_follow_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_env_follow_reset_state(const bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state) {
-	bw_one_pole_reset_state(&coeffs->one_pole_coeffs, &state->one_pole_state, 0.f);
+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_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(bw_is_finite(x_0));
+
+	const float x = bw_absf(x_0);
+	const float y = bw_one_pole_reset_state(&coeffs->one_pole_coeffs, &state->one_pole_state, x);
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_env_follow_state");
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	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(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_env_follow_update_coeffs_ctrl(bw_env_follow_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_env_follow_reset_state_multi(
+		const bw_env_follow_coeffs * BW_RESTRICT              coeffs,
+		bw_env_follow_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float *                                   x_0,
+		float *                                         y_0,
+		size_t                                          n_channels) {
+	BW_ASSERT(coeffs != 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(x_0 != NULL);
+
+	if (y_0 != 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
+		for (size_t i = 0; i < n_channels; i++)
+			bw_env_follow_reset_state(coeffs, state[i], x_0[i]);
+
+	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);
+}
+
+static inline void bw_env_follow_update_coeffs_ctrl(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
+
 	bw_one_pole_update_coeffs_ctrl(&coeffs->one_pole_coeffs);
+
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_env_follow_update_coeffs_audio(bw_env_follow_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_env_follow_update_coeffs_audio(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
+
 	bw_one_pole_update_coeffs_audio(&coeffs->one_pole_coeffs);
+
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 }
 
-static inline float bw_env_follow_process1(const bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state, float x) {
+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_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_DEEP(bw_env_follow_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(x));
+
 	x = bw_absf(x);
-	return bw_one_pole_process1_asym(&coeffs->one_pole_coeffs, &state->one_pole_state, x);
+	const float y = bw_one_pole_process1_asym(&coeffs->one_pole_coeffs, &state->one_pole_state, x);
+
+	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(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_env_follow_process(bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples) {
+static inline void bw_env_follow_process(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs,
+		bw_env_follow_state * BW_RESTRICT  state,
+		const float *                      x,
+		float *                            y,
+		size_t                             n_samples) {
+	BW_ASSERT(coeffs != 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_DEEP(bw_env_follow_state_is_valid(coeffs, state));
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+
 	bw_env_follow_update_coeffs_ctrl(coeffs);
 	if (y != NULL)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -248,9 +483,26 @@ static inline void bw_env_follow_process(bw_env_follow_coeffs *BW_RESTRICT coeff
 			bw_env_follow_update_coeffs_audio(coeffs);
 			bw_env_follow_process1(coeffs, state, x[i]);
 		}
+
+	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);
 }
 
-static inline void bw_env_follow_process_multi(bw_env_follow_coeffs *BW_RESTRICT coeffs, bw_env_follow_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, float * const *y, size_t n_channels, size_t n_samples) {
+static inline void bw_env_follow_process_multi(
+		bw_env_follow_coeffs * BW_RESTRICT                    coeffs,
+		bw_env_follow_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float * const *                                 x,
+		float * const *                                       y,
+		size_t                                                n_channels,
+		size_t                                                n_samples) {
+	BW_ASSERT(coeffs != 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(x != NULL);
+
 	bw_env_follow_update_coeffs_ctrl(coeffs);
 	if (y != NULL)
 		for (size_t i = 0; i < n_samples; i++) {
@@ -267,20 +519,81 @@ static inline void bw_env_follow_process_multi(bw_env_follow_coeffs *BW_RESTRICT
 			for (size_t j = 0; j < n_channels; j++)
 				bw_env_follow_process1(coeffs, state[j], x[j][i]);
 		}
+
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_env_follow_set_attack_tau(bw_env_follow_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_env_follow_set_attack_tau(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs,
+		float                              value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f);
+
 	bw_one_pole_set_tau_up(&coeffs->one_pole_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_init);
 }
 
-static inline void bw_env_follow_set_release_tau(bw_env_follow_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_env_follow_set_release_tau(
+		bw_env_follow_coeffs * BW_RESTRICT coeffs,
+		float                              value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f);
+
 	bw_one_pole_set_tau_down(&coeffs->one_pole_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_env_follow_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_env_follow_coeffs_state_init);
 }
 
-static inline float bw_env_follow_get_y_z1(const bw_env_follow_state *BW_RESTRICT state) {
+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));
+
 	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);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_env_follow_coeffs"))
+		return 0;
+	if (coeffs->state < bw_env_follow_coeffs_state_init || coeffs->state > bw_env_follow_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	return bw_one_pole_coeffs_is_valid(&coeffs->one_pole_coeffs);
+}
+
+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);
+
+#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)
+		return 0;
+#endif
+
+	(void)coeffs;
+
+	return bw_one_pole_state_is_valid(&coeffs->one_pole_coeffs, &state->one_pole_state);
+}
+
 #ifdef __cplusplus
 }
 
@@ -298,21 +611,43 @@ class EnvFollow {
 public:
 	EnvFollow();
 
-	void setSampleRate(float sampleRate);
-	void reset();
+	void setSampleRate(
+		float sampleRate);
+
+	void reset(
+		float               x0 = 0.f,
+		float * BW_RESTRICT y0 = nullptr);
+
+	void reset(
+		float                                       x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0);
+
+	void reset(
+		const float * x0,
+		float *       y0 = nullptr);
+
+	void reset(
+		std::array<float, N_CHANNELS>               x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0 = nullptr);
+
 	void process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples);
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples);
+
 	void process(
 		std::array<const float *, N_CHANNELS> x,
-		std::array<float *, N_CHANNELS> y,
-		size_t nSamples);
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples);
 
-	void setAttackTau(float value);
-	void setReleaseTau(float value);
-	
-	float getYZ1(size_t channel);
+	void setAttackTau(
+		float value);
+
+	void setReleaseTau(
+		float value);
+
+	float getYZ1(
+		size_t channel);
 /*! <<<...
  *  }
  *  ```
@@ -324,9 +659,9 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_env_follow_coeffs	 coeffs;
-	bw_env_follow_state	 states[N_CHANNELS];
-	bw_env_follow_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_env_follow_coeffs			coeffs;
+	bw_env_follow_state			states[N_CHANNELS];
+	bw_env_follow_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -337,45 +672,77 @@ inline EnvFollow<N_CHANNELS>::EnvFollow() {
 }
 
 template<size_t N_CHANNELS>
-inline void EnvFollow<N_CHANNELS>::setSampleRate(float sampleRate) {
+inline void EnvFollow<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
 	bw_env_follow_set_sample_rate(&coeffs, sampleRate);
 }
 
 template<size_t N_CHANNELS>
-inline void EnvFollow<N_CHANNELS>::reset() {
+inline void EnvFollow<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
 	bw_env_follow_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_env_follow_reset_state(&coeffs, states + i);
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_env_follow_reset_state(&coeffs, states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_env_follow_reset_state(&coeffs, states + i, x0);
+}
+
+template<size_t N_CHANNELS>
+inline void EnvFollow<N_CHANNELS>::reset(
+		float                                       x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
+	reset(x0, y0 != nullptr ? y0->data() : nullptr);
+}
+
+template<size_t N_CHANNELS>
+inline void EnvFollow<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_env_follow_reset_coeffs(&coeffs);
+	bw_env_follow_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void EnvFollow<N_CHANNELS>::reset(
+		std::array<float, N_CHANNELS>               x0,
+		std::array<float, N_CHANNELS> * BW_RESTRICT y0) {
+	reset(x0.data(), y0 != nullptr ? y0->data() : nullptr);
 }
 
 template<size_t N_CHANNELS>
 inline void EnvFollow<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_env_follow_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void EnvFollow<N_CHANNELS>::process(
 		std::array<const float *, N_CHANNELS> x,
-		std::array<float *, N_CHANNELS> y,
-		size_t nSamples) {
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples) {
 	process(x.data(), y.data(), nSamples);
 }
 
 template<size_t N_CHANNELS>
-inline void EnvFollow<N_CHANNELS>::setAttackTau(float value) {
+inline void EnvFollow<N_CHANNELS>::setAttackTau(
+		float value) {
 	bw_env_follow_set_attack_tau(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void EnvFollow<N_CHANNELS>::setReleaseTau(float value) {
+inline void EnvFollow<N_CHANNELS>::setReleaseTau(
+		float value) {
 	bw_env_follow_set_release_tau(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline float EnvFollow<N_CHANNELS>::getYZ1(size_t channel) {
+inline float EnvFollow<N_CHANNELS>::getYZ1(
+		size_t channel) {
 	return bw_env_follow_get_y_z1(states + channel);
 }