diff --git a/examples/fx_drive/src/bw_example_fx_drive.c b/examples/fx_drive/src/bw_example_fx_drive.c
index aefe129..0091efd 100644
--- a/examples/fx_drive/src/bw_example_fx_drive.c
+++ b/examples/fx_drive/src/bw_example_fx_drive.c
@@ -32,7 +32,7 @@ void bw_example_fx_drive_set_sample_rate(bw_example_fx_drive *instance, float sa
 
 void bw_example_fx_drive_reset(bw_example_fx_drive *instance) {
 	bw_drive_reset_coeffs(&instance->drive_coeffs);
-	bw_drive_reset_state(&instance->drive_coeffs, &instance->drive_state);
+	bw_drive_reset_state(&instance->drive_coeffs, &instance->drive_state, 0.f);
 	bw_src_int_reset_state(&instance->src_up_coeffs, &instance->src_up_state, 0.f);
 	bw_src_int_reset_state(&instance->src_down_coeffs, &instance->src_down_state, 0.f);
 }
diff --git a/examples/fx_drive/vst3/Makefile b/examples/fx_drive/vst3/Makefile
index e85999a..294a59e 100644
--- a/examples/fx_drive/vst3/Makefile
+++ b/examples/fx_drive/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fx_drive
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fx_drive.c
 
 include ${ROOT_DIR}/../../common/vst3/vst3.mk
+
+CXXFLAGS += -DRELEASE=1 -DNDEBUG -DBW_NO_DEBUG
+#CXXFLAGS += -DDEVELOPMENT=1 -DBW_DEBUG_DEEP
diff --git a/examples/fxpp_drive/vst3/Makefile b/examples/fxpp_drive/vst3/Makefile
index fe25961..32524ea 100644
--- a/examples/fxpp_drive/vst3/Makefile
+++ b/examples/fxpp_drive/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fxpp_drive
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fxpp_drive.cpp
 
 include ${ROOT_DIR}/../../common/vst3/vst3.mk
+
+CXXFLAGS += -DRELEASE=1 -DNDEBUG -DBW_NO_DEBUG
+#CXXFLAGS += -DDEVELOPMENT=1 -DBW_DEBUG_DEEP
diff --git a/include/bw_clip.h b/include/bw_clip.h
index ea0e94b..8d27e12 100644
--- a/include/bw_clip.h
+++ b/include/bw_clip.h
@@ -425,7 +425,7 @@ static inline float bw_clip_reset_state(
 	const float a = bw_absf(x);
 	const float F = a > 1.f ? a - 0.5f : 0.5f * a * a;
 	const float yb = bw_clipf(x, -1.f, 1.f);
-	const float y = yb - coeffs->bias_dc;
+	const float y = (coeffs->gain_compensation ? coeffs->inv_gain : 1.f) * (yb - coeffs->bias_dc);
 	state->x_z1 = x;
 	state->F_z1 = F;
 
diff --git a/include/bw_dist.h b/include/bw_dist.h
index aad2222..346fa08 100644
--- a/include/bw_dist.h
+++ b/include/bw_dist.h
@@ -34,6 +34,7 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
+ *          <li>Adjusted internal peak cutoff to more sensible value.</li>
  *          <li>Added initial input value to
  *              <code>bw_dist_reset_state()</code>.</li>
  *          <li>Added <code>bw_dist_reset_state_multi()</code> and updated C++
@@ -42,7 +43,6 @@
  *              output value.</li>
  *          <li>Added overloaded C++ <code>reset()</code> functions taking
  *              arrays as arguments.</li>
- *          <li>Adjusted internal peak cutoff to more sensible value.</li>
  *          <li><code>bw_dist_process()</code> and
  *              <code>bw_dist_process_multi()</code> now use <code>size_t</code>
  *              to count samples and channels.</li>
diff --git a/include/bw_drive.h b/include/bw_drive.h
index 4dfe773..fd01afd 100644
--- a/include/bw_drive.h
+++ b/include/bw_drive.h
@@ -3,11 +3,11 @@
  *
  * Copyright (C) 2023 Orastron Srl unipersonale
  *
- * Brickworks is free software: you can redistribute it and/or modify
+ * Brickworks is free software: you can redriveribute it and/or modify
  * it under the terms of the GNU General Public License as published by
  * the Free Software Foundation, version 3 of the License.
  *
- * Brickworks is distributed in the hope that it will be useful,
+ * Brickworks is driveributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
@@ -36,6 +36,12 @@
  *        <ul>
  *          <li>Improved algorithm to be a bit more faithful to the
  *              original.</li>
+ *          <li>Added <code>bw_drive_reset_state_multi()</code> and updated C++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_drive_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_drive_process()</code> and
  *              <code>bw_drive_process_multi()</code> now use
  *              <code>size_t</code> to count samples and channels.</li>
@@ -45,6 +51,8 @@
  *          <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>:
@@ -85,50 +93,86 @@ typedef struct bw_drive_state bw_drive_state;
  *
  *    #### bw_drive_init()
  *  ```>>> */
-static inline void bw_drive_init(bw_drive_coeffs *BW_RESTRICT coeffs);
+static inline void bw_drive_init(
+	bw_drive_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
  *    #### bw_drive_set_sample_rate()
  *  ```>>> */
-static inline void bw_drive_set_sample_rate(bw_drive_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_drive_set_sample_rate(
+	bw_drive_coeffs * BW_RESTRICT coeffs,
+	float                         sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_drive_reset_coeffs()
  *  ```>>> */
-static inline void bw_drive_reset_coeffs(bw_drive_coeffs *BW_RESTRICT coeffs);
+static inline void bw_drive_reset_coeffs(
+	bw_drive_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_drive_reset_state()
  *  ```>>> */
-static inline void bw_drive_reset_state(const bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state);
+static inline float bw_drive_reset_state(
+	const bw_drive_coeffs * BW_RESTRICT coeffs,
+	bw_drive_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_drive_reset_state_multi()
+ *  ```>>> */
+static inline void bw_drive_reset_state_multi(
+	const bw_drive_coeffs * BW_RESTRICT              coeffs,
+	bw_drive_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_drive_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_drive_update_coeffs_ctrl(bw_drive_coeffs *BW_RESTRICT coeffs);
+static inline void bw_drive_update_coeffs_ctrl(
+	bw_drive_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_drive_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_drive_update_coeffs_audio(bw_drive_coeffs *BW_RESTRICT coeffs);
+static inline void bw_drive_update_coeffs_audio(
+	bw_drive_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_drive_process1()
  *  ```>>> */
-static inline float bw_drive_process1(const bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state, float x);
+static inline float bw_drive_process1(
+	const bw_drive_coeffs * BW_RESTRICT coeffs,
+	bw_drive_state * BW_RESTRICT        state,
+	float                               x);
 /*! <<<```
  *    Processes one input sample `x` using `coeffs`, while using and updating
  *    `state`. Returns the corresponding output sample.
  *
  *    #### bw_drive_process()
  *  ```>>> */
-static inline void bw_drive_process(bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples);
+static inline void bw_drive_process(
+	bw_drive_coeffs * BW_RESTRICT coeffs,
+	bw_drive_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
@@ -136,7 +180,13 @@ static inline void bw_drive_process(bw_drive_coeffs *BW_RESTRICT coeffs, bw_driv
  *
  *    #### bw_drive_process_multi()
  *  ```>>> */
-static inline void bw_drive_process_multi(bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_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_drive_process_multi(
+	bw_drive_coeffs * BW_RESTRICT                    coeffs,
+	bw_drive_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
@@ -145,29 +195,68 @@ static inline void bw_drive_process_multi(bw_drive_coeffs *BW_RESTRICT coeffs, b
  *
  *    #### bw_drive_set_drive()
  *  ```>>> */
-static inline void bw_drive_set_drive(bw_drive_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_drive_set_drive(
+	bw_drive_coeffs * BW_RESTRICT coeffs,
+	float value);
 /*! <<<```
  *    Sets the overdrive (input gain, approximately) to the given `value` in
- *    [`0.f`, `1.f`] in `coeffs`.
+ *    `coeffs`.
+ *
+ *    Valid range: [`0.f` (low overdrive), `1.f` (high overdrive)].
  *
  *    Default value: `0.f`.
  *
  *    #### bw_drive_set_tone()
  *  ```>>> */
-static inline void bw_drive_set_tone(bw_drive_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_drive_set_tone(
+	bw_drive_coeffs * BW_RESTRICT coeffs,
+	float value);
 /*! <<<```
- *    Sets the tone (filter) to the given `value` in [`0.f`, `1.f`] in `coeffs`.
+ *    Sets the tone (filter) to the given `value` in `coeffs`.
+ *
+ *    Valid range: [`0.f` (low cutoff), `1.f` (high cutoff)].
  *
  *    Default value: `0.5f`.
  *
  *    #### bw_drive_set_volume()
  *  ```>>> */
-static inline void bw_drive_set_volume(bw_drive_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_drive_set_volume(
+	bw_drive_coeffs * BW_RESTRICT coeffs,
+	float value);
 /*! <<<```
- *    Sets the volume (output gain) to the given `value` in [`0.f`, `1.f`] in
- *    `coeffs`.
+ *    Sets the volume (output gain) to the given `value` in `coeffs`.
+ *
+ *    Valid range: [`0.f` (silence), `1.f` (max volume)].
  *
  *    Default value: `1.f`.
+ *
+ *    #### bw_drive_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_drive_coeffs_is_valid(
+	const bw_drive_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_drive_coeffs`.
+ *
+ *    #### bw_drive_state_is_valid()
+ *  ```>>> */
+static inline char bw_drive_state_is_valid(
+	const bw_drive_coeffs * BW_RESTRICT coeffs,
+	const bw_drive_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_drive_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -190,17 +279,37 @@ static inline void bw_drive_set_volume(bw_drive_coeffs *BW_RESTRICT coeffs, floa
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_drive_coeffs_state {
+	bw_drive_coeffs_state_invalid,
+	bw_drive_coeffs_state_init,
+	bw_drive_coeffs_state_set_sample_rate,
+	bw_drive_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_drive_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_drive_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_svf_coeffs	hp2_coeffs;
-	bw_hs1_coeffs	hs1_coeffs;
-	bw_peak_coeffs	peak_coeffs;
-	bw_satur_coeffs	satur_coeffs;
-	bw_lp1_coeffs	lp1_coeffs;
-	bw_gain_coeffs	gain_coeffs;
+	bw_svf_coeffs			hp2_coeffs;
+	bw_hs1_coeffs			hs1_coeffs;
+	bw_peak_coeffs			peak_coeffs;
+	bw_satur_coeffs			satur_coeffs;
+	bw_lp1_coeffs			lp1_coeffs;
+	bw_gain_coeffs			gain_coeffs;
 };
 
 struct bw_drive_state {
+#ifdef BW_DEBUG_DEEP
+	uint32_t	hash;
+	uint32_t	coeffs_reset_id;
+#endif
+
 	// Sub-components
 	bw_svf_state	hp2_state;
 	bw_hs1_state	hs1_state;
@@ -209,7 +318,10 @@ struct bw_drive_state {
 	bw_lp1_state	lp1_state;
 };
 
-static inline void bw_drive_init(bw_drive_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_drive_init(
+		bw_drive_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	bw_svf_init(&coeffs->hp2_coeffs);
 	bw_hs1_init(&coeffs->hs1_coeffs);
 	bw_peak_init(&coeffs->peak_coeffs);
@@ -225,9 +337,24 @@ static inline void bw_drive_init(bw_drive_coeffs *BW_RESTRICT coeffs) {
 	bw_satur_set_gain(&coeffs->satur_coeffs, 1.5f);
 	bw_satur_set_gain_compensation(&coeffs->satur_coeffs, 1);
 	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 400.f + (5e3f - 400.f) * 0.125f);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_drive_coeffs");
+	coeffs->state = bw_drive_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_init);
 }
 
-static inline void bw_drive_set_sample_rate(bw_drive_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+static inline void bw_drive_set_sample_rate(
+		bw_drive_coeffs * BW_RESTRICT coeffs,
+		float                         sample_rate) {
+	BW_ASSERT(coeffs != 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);
+
 	bw_svf_set_sample_rate(&coeffs->hp2_coeffs, sample_rate);
 	bw_hs1_set_sample_rate(&coeffs->hs1_coeffs, sample_rate);
 	bw_peak_set_sample_rate(&coeffs->peak_coeffs, sample_rate);
@@ -237,71 +364,277 @@ static inline void bw_drive_set_sample_rate(bw_drive_coeffs *BW_RESTRICT coeffs,
 	bw_svf_reset_coeffs(&coeffs->hp2_coeffs);
 	bw_hs1_reset_coeffs(&coeffs->hs1_coeffs);
 	bw_satur_reset_coeffs(&coeffs->satur_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_drive_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_drive_reset_coeffs(bw_drive_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_drive_reset_coeffs(
+		bw_drive_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_set_sample_rate);
+
 	bw_peak_reset_coeffs(&coeffs->peak_coeffs);
 	bw_lp1_reset_coeffs(&coeffs->lp1_coeffs);
 	bw_gain_reset_coeffs(&coeffs->gain_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_drive_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_drive_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_drive_reset_state(const bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state) {
-	bw_svf_reset_state(&coeffs->hp2_coeffs, &state->hp2_state, 0.f);
-	bw_hs1_reset_state(&coeffs->hs1_coeffs, &state->hs1_state, 0.f);
-	bw_peak_reset_state(&coeffs->peak_coeffs, &state->peak_state, 0.f);
-	bw_satur_reset_state(&coeffs->satur_coeffs, &state->satur_state);
-	bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, 0.f);
+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_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(bw_is_finite(x_0));
+
+	float v_lp, v_hp, v_bp;
+	bw_svf_reset_state(&coeffs->hp2_coeffs, &state->hp2_state, 0.316f * x_0, &v_lp, &v_bp, &v_hp);
+	float y = bw_hs1_reset_state(&coeffs->hs1_coeffs, &state->hs1_state, v_hp);
+	y = bw_peak_reset_state(&coeffs->peak_coeffs, &state->peak_state, y);
+	y = v_hp + bw_satur_reset_state(&coeffs->satur_coeffs, &state->satur_state, y - v_hp);
+	y = bw_lp1_reset_state(&coeffs->lp1_coeffs, &state->lp1_state, y);
+	y = bw_gain_get_gain_cur(&coeffs->gain_coeffs) * y;
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_drive_state");
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_drive_update_coeffs_ctrl(bw_drive_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_drive_reset_state_multi(
+		const bw_drive_coeffs * BW_RESTRICT              coeffs,
+		bw_drive_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_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_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_drive_reset_state(coeffs, state[i], x_0[i]);
+	else
+		for (size_t i = 0; i < n_channels; i++)
+			bw_drive_reset_state(coeffs, state[i], x_0[i]);
+
+	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);
+}
+
+static inline void bw_drive_update_coeffs_ctrl(
+		bw_drive_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+
 	bw_peak_update_coeffs_ctrl(&coeffs->peak_coeffs);
 	bw_lp1_update_coeffs_ctrl(&coeffs->lp1_coeffs);
 	bw_gain_update_coeffs_ctrl(&coeffs->gain_coeffs);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_drive_update_coeffs_audio(bw_drive_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_drive_update_coeffs_audio(
+		bw_drive_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+
 	bw_peak_update_coeffs_audio(&coeffs->peak_coeffs);
 	bw_lp1_update_coeffs_audio(&coeffs->lp1_coeffs);
 	bw_gain_update_coeffs_audio(&coeffs->gain_coeffs);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
 }
 
-static inline float bw_drive_process1(const bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state, float x) {
+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_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(x));
+
 	float v_lp, v_hp, v_bp;
 	bw_svf_process1(&coeffs->hp2_coeffs, &state->hp2_state, 0.316f * x, &v_lp, &v_bp, &v_hp);
 	float y = bw_hs1_process1(&coeffs->hs1_coeffs, &state->hs1_state, v_hp);
 	y = bw_peak_process1(&coeffs->peak_coeffs, &state->peak_state, y);
 	y = v_hp + bw_satur_process1_comp(&coeffs->satur_coeffs, &state->satur_state, y - v_hp);
 	y = bw_lp1_process1(&coeffs->lp1_coeffs, &state->lp1_state, y);
-	return bw_gain_process1(&coeffs->gain_coeffs, y);
+	y = bw_gain_process1(&coeffs->gain_coeffs, y);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_drive_process(bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples) {
+static inline void bw_drive_process(
+		bw_drive_coeffs * BW_RESTRICT coeffs,
+		bw_drive_state * BW_RESTRICT  state,
+		const float *                 x,
+		float *                       y,
+		size_t                        n_samples) {
+	BW_ASSERT(coeffs != 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_DEEP(bw_drive_state_is_valid(coeffs, state));
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
 	bw_drive_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_drive_update_coeffs_audio(coeffs);
 		y[i] = bw_drive_process1(coeffs, state, x[i]);
 	}
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_drive_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
-static inline void bw_drive_process_multi(bw_drive_coeffs *BW_RESTRICT coeffs, bw_drive_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_drive_process_multi(
+		bw_drive_coeffs * BW_RESTRICT                    coeffs,
+		bw_drive_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_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	bw_drive_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_drive_update_coeffs_audio(coeffs);
 		for (size_t j = 0; j < n_channels; j++)
 			y[j][i] = bw_drive_process1(coeffs, state[j], x[j][i]);
 	}
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_drive_set_drive(bw_drive_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_drive_set_drive(
+		bw_drive_coeffs * BW_RESTRICT coeffs,
+		float                         value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_peak_set_peak_gain_dB(&coeffs->peak_coeffs, 20.f * value);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 }
 
-static inline void bw_drive_set_tone(bw_drive_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_drive_set_tone(
+		bw_drive_coeffs * BW_RESTRICT coeffs,
+		float                         value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 400.f + (5e3f - 400.f) * value * value * value);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
 }
 
-static inline void bw_drive_set_volume(bw_drive_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_drive_set_volume(
+		bw_drive_coeffs * BW_RESTRICT coeffs,
+		float                         value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_gain_set_gain_lin(&coeffs->gain_coeffs, value * value * value);
+
+	BW_ASSERT_DEEP(bw_drive_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_drive_coeffs_state_init);
+}
+
+static inline char bw_drive_coeffs_is_valid(
+		const bw_drive_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_drive_coeffs"))
+		return 0;
+	if (coeffs->state < bw_drive_coeffs_state_init || coeffs->state > bw_drive_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	return bw_svf_coeffs_is_valid(&coeffs->hp2_coeffs)
+		&& bw_hs1_coeffs_is_valid(&coeffs->hs1_coeffs)
+		&& bw_peak_coeffs_is_valid(&coeffs->peak_coeffs)
+		&& bw_satur_coeffs_is_valid(&coeffs->satur_coeffs)
+		&& bw_lp1_coeffs_is_valid(&coeffs->lp1_coeffs)
+		&& bw_gain_coeffs_is_valid(&coeffs->gain_coeffs);
+}
+
+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);
+
+#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)
+		return 0;
+#endif
+
+	(void)coeffs;
+
+	return bw_svf_state_is_valid(&coeffs->hp2_coeffs, &state->hp2_state)
+		&& bw_hs1_state_is_valid(&coeffs->hs1_coeffs, &state->hs1_state)
+		&& bw_peak_state_is_valid(&coeffs->peak_coeffs, &state->peak_state)
+		&& bw_satur_state_is_valid(&coeffs->satur_coeffs, &state->satur_state)
+		&& bw_lp1_state_is_valid(&coeffs->lp1_coeffs, &state->lp1_state);
 }
 
 #ifdef __cplusplus
@@ -321,20 +654,43 @@ class Drive {
 public:
 	Drive();
 
-	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 setDrive(float value);
-	void setTone(float value);
-	void setVolume(float value);
+	void setDrive(
+		float value);
+
+	void setTone(
+		float value);
+
+	void setVolume(
+		float value);
 /*! <<<...
  *  }
  *  ```
@@ -346,9 +702,9 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_drive_coeffs	 coeffs;
-	bw_drive_state	 states[N_CHANNELS];
-	bw_drive_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_drive_coeffs			coeffs;
+	bw_drive_state			states[N_CHANNELS];
+	bw_drive_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -359,45 +715,77 @@ inline Drive<N_CHANNELS>::Drive() {
 }
 
 template<size_t N_CHANNELS>
-inline void Drive<N_CHANNELS>::setSampleRate(float sampleRate) {
+inline void Drive<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
 	bw_drive_set_sample_rate(&coeffs, sampleRate);
 }
 
 template<size_t N_CHANNELS>
-inline void Drive<N_CHANNELS>::reset() {
+inline void Drive<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
 	bw_drive_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_drive_reset_state(&coeffs, states + i);
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_drive_reset_state(&coeffs, states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_drive_reset_state(&coeffs, states + i, x0);
+}
+
+template<size_t N_CHANNELS>
+inline void Drive<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 Drive<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_drive_reset_coeffs(&coeffs);
+	bw_drive_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void Drive<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 Drive<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_drive_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void Drive<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 Drive<N_CHANNELS>::setDrive(float value) {
+inline void Drive<N_CHANNELS>::setDrive(
+		float value) {
 	bw_drive_set_drive(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Drive<N_CHANNELS>::setTone(float value) {
+inline void Drive<N_CHANNELS>::setTone(
+		float value) {
 	bw_drive_set_tone(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Drive<N_CHANNELS>::setVolume(float value) {
+inline void Drive<N_CHANNELS>::setVolume(
+		float value) {
 	bw_drive_set_volume(&coeffs, value);
 }
 
diff --git a/include/bw_satur.h b/include/bw_satur.h
index 0b0104b..fd8fff1 100644
--- a/include/bw_satur.h
+++ b/include/bw_satur.h
@@ -445,7 +445,7 @@ static inline float bw_satur_reset_state(
 	const float ax = bw_absf(x);
 	const float F = ax >= 2.115287308554551f ? ax - 0.6847736211329452f : ax * ax * ((0.00304518315009429f * ax - 0.09167437770414569f) * ax + 0.5f);
 	const float yb = bw_satur_tanhf(x);
-	const float y = yb - coeffs->bias_dc;
+	const float y = (coeffs->gain_compensation ? coeffs->inv_gain : 1.f) * (yb - coeffs->bias_dc);
 	state->x_z1 = x;
 	state->F_z1 = F;