diff --git a/TODO b/TODO
index 151a051..092ccb9 100644
--- a/TODO
+++ b/TODO
@@ -30,6 +30,7 @@ finally:
 * state that audio cannot be inf (also in reset)
 * state that you need different output buffers to reset
 * thank scientific paper authors
+* change config.h in examples version 1.0.0
 
 build system:
 * single header generation (vs modules in bwp... to think about)
diff --git a/examples/fx_dist/src/bw_example_fx_dist.c b/examples/fx_dist/src/bw_example_fx_dist.c
index 5b78c91..e6be37c 100644
--- a/examples/fx_dist/src/bw_example_fx_dist.c
+++ b/examples/fx_dist/src/bw_example_fx_dist.c
@@ -32,7 +32,7 @@ void bw_example_fx_dist_set_sample_rate(bw_example_fx_dist *instance, float samp
 
 void bw_example_fx_dist_reset(bw_example_fx_dist *instance) {
 	bw_dist_reset_coeffs(&instance->dist_coeffs);
-	bw_dist_reset_state(&instance->dist_coeffs, &instance->dist_state);
+	bw_dist_reset_state(&instance->dist_coeffs, &instance->dist_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_dist/vst3/Makefile b/examples/fx_dist/vst3/Makefile
index ae091c2..f2624c8 100644
--- a/examples/fx_dist/vst3/Makefile
+++ b/examples/fx_dist/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fx_dist
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fx_dist.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_dist/vst3/Makefile b/examples/fxpp_dist/vst3/Makefile
index 158a5f5..6493bca 100644
--- a/examples/fxpp_dist/vst3/Makefile
+++ b/examples/fxpp_dist/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fxpp_dist
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_fxpp_dist.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_dist.h b/include/bw_dist.h
index fb01de1..aad2222 100644
--- a/include/bw_dist.h
+++ b/include/bw_dist.h
@@ -34,8 +34,12 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
- *          <li>Added initial value argument in
+ *          <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++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_dist_reset_state()</code> returns the initial
+ *              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>
@@ -48,6 +52,8 @@
  *          <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>:
@@ -88,51 +94,86 @@ typedef struct bw_dist_state bw_dist_state;
  *
  *    #### bw_dist_init()
  *  ```>>> */
-static inline void bw_dist_init(bw_dist_coeffs *BW_RESTRICT coeffs);
+static inline void bw_dist_init(
+	bw_dist_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Initializes input parameter values in `coeffs`.
  *
  *    #### bw_dist_set_sample_rate()
  *  ```>>> */
-static inline void bw_dist_set_sample_rate(bw_dist_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_dist_set_sample_rate(
+	bw_dist_coeffs * BW_RESTRICT coeffs,
+	float                        sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_dist_reset_coeffs()
  *  ```>>> */
-static inline void bw_dist_reset_coeffs(bw_dist_coeffs *BW_RESTRICT coeffs);
+static inline void bw_dist_reset_coeffs(
+	bw_dist_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_dist_reset_state()
  *  ```>>> */
-static inline void bw_dist_reset_state(const bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, float x_0);
+static inline float bw_dist_reset_state(
+	const bw_dist_coeffs * BW_RESTRICT coeffs,
+	bw_dist_state * BW_RESTRICT        state,
+	float                              x_0);
 /*! <<<```
  *    Resets the given `state` to its initial values using the given `coeffs`
- *    and the quiescent/initial input value `x_0`.
+ *    and the initial input value `x_0`.
+ *
+ *    Returns the corresponding initial output value.
+ *
+ *    #### bw_dist_reset_state_multi()
+ *  ```>>> */
+static inline void bw_dist_reset_state_multi(
+	const bw_dist_coeffs * BW_RESTRICT              coeffs,
+	bw_dist_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_dist_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_dist_update_coeffs_ctrl(bw_dist_coeffs *BW_RESTRICT coeffs);
+static inline void bw_dist_update_coeffs_ctrl(
+	bw_dist_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_dist_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_dist_update_coeffs_audio(bw_dist_coeffs *BW_RESTRICT coeffs);
+static inline void bw_dist_update_coeffs_audio(
+	bw_dist_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_dist_process1()
  *  ```>>> */
-static inline float bw_dist_process1(const bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, float x);
+static inline float bw_dist_process1(
+	const bw_dist_coeffs * BW_RESTRICT coeffs,
+	bw_dist_state * BW_RESTRICT        state,
+	float                              x);
 /*! <<<```
  *    Processes one input sample `x` using `coeffs`, while using and updating
  *    `state`. Returns the corresponding output sample.
  *
  *    #### bw_dist_process()
  *  ```>>> */
-static inline void bw_dist_process(bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples);
+static inline void bw_dist_process(
+	bw_dist_coeffs * BW_RESTRICT coeffs,
+	bw_dist_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
@@ -140,7 +181,13 @@ static inline void bw_dist_process(bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_s
  *
  *    #### bw_dist_process_multi()
  *  ```>>> */
-static inline void bw_dist_process_multi(bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_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_dist_process_multi(
+	bw_dist_coeffs * BW_RESTRICT                    coeffs,
+	bw_dist_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
@@ -149,29 +196,68 @@ static inline void bw_dist_process_multi(bw_dist_coeffs *BW_RESTRICT coeffs, bw_
  *
  *    #### bw_dist_set_distortion()
  *  ```>>> */
-static inline void bw_dist_set_distortion(bw_dist_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_dist_set_distortion(
+	bw_dist_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the distortion (input gain, approximately) to the given `value` in
- *    [`0.f`, `1.f`] in `coeffs`.
+ *    `coeffs`.
+ *
+ *    Valid range: [`0.f` (low distortion), `1.f` (high distortion)].
  *
  *    Default value: `0.f`.
  *
  *    #### bw_dist_set_tone()
  *  ```>>> */
-static inline void bw_dist_set_tone(bw_dist_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_dist_set_tone(
+	bw_dist_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_dist_set_volume()
  *  ```>>> */
-static inline void bw_dist_set_volume(bw_dist_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_dist_set_volume(
+	bw_dist_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_dist_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_dist_coeffs_is_valid(
+	const bw_dist_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_dist_coeffs`.
+ *
+ *    #### bw_dist_state_is_valid()
+ *  ```>>> */
+static inline char bw_dist_state_is_valid(
+	const bw_dist_coeffs * BW_RESTRICT coeffs,
+	const bw_dist_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_dist_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -194,17 +280,37 @@ static inline void bw_dist_set_volume(bw_dist_coeffs *BW_RESTRICT coeffs, float
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_dist_coeffs_state {
+	bw_dist_coeffs_state_invalid,
+	bw_dist_coeffs_state_init,
+	bw_dist_coeffs_state_set_sample_rate,
+	bw_dist_coeffs_state_reset_coeffs
+};
+#endif
+
 struct bw_dist_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_dist_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_hp1_coeffs	hp1_coeffs;
-	bw_peak_coeffs	peak_coeffs;
-	bw_clip_coeffs	clip_coeffs;
-	bw_satur_coeffs	satur_coeffs;
-	bw_lp1_coeffs	lp1_coeffs;
-	bw_gain_coeffs	gain_coeffs;
+	bw_hp1_coeffs			hp1_coeffs;
+	bw_peak_coeffs			peak_coeffs;
+	bw_clip_coeffs			clip_coeffs;
+	bw_satur_coeffs			satur_coeffs;
+	bw_lp1_coeffs			lp1_coeffs;
+	bw_gain_coeffs			gain_coeffs;
 };
 
 struct bw_dist_state {
+#ifdef BW_DEBUG_DEEP
+	uint32_t	hash;
+	uint32_t	coeffs_reset_id;
+#endif
+
 	// Sub-components
 	bw_hp1_state	hp1_state;
 	bw_peak_state	peak_state;
@@ -213,7 +319,10 @@ struct bw_dist_state {
 	bw_lp1_state	lp1_state;
 };
 
-static inline void bw_dist_init(bw_dist_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_dist_init(
+		bw_dist_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
 	bw_hp1_init(&coeffs->hp1_coeffs);
 	bw_peak_init(&coeffs->peak_coeffs);
 	bw_clip_init(&coeffs->clip_coeffs);
@@ -229,9 +338,24 @@ static inline void bw_dist_init(bw_dist_coeffs *BW_RESTRICT coeffs) {
 	bw_satur_set_gain(&coeffs->satur_coeffs, 1.f / 0.7f);
 	bw_satur_set_gain_compensation(&coeffs->satur_coeffs, 1);
 	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 475.f + (20e3f - 475.f) * 0.125f);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_dist_coeffs");
+	coeffs->state = bw_dist_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_dist_coeffs_state_init);
 }
 
-static inline void bw_dist_set_sample_rate(bw_dist_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+static inline void bw_dist_set_sample_rate(
+		bw_dist_coeffs * BW_RESTRICT coeffs,
+		float                        sample_rate) {
+	BW_ASSERT(coeffs != 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);
+
 	bw_hp1_set_sample_rate(&coeffs->hp1_coeffs, sample_rate);
 	bw_peak_set_sample_rate(&coeffs->peak_coeffs, sample_rate);
 	bw_clip_set_sample_rate(&coeffs->clip_coeffs, sample_rate);
@@ -241,70 +365,275 @@ static inline void bw_dist_set_sample_rate(bw_dist_coeffs *BW_RESTRICT coeffs, f
 	bw_hp1_reset_coeffs(&coeffs->hp1_coeffs);
 	bw_clip_reset_coeffs(&coeffs->clip_coeffs);
 	bw_satur_reset_coeffs(&coeffs->satur_coeffs);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_dist_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_dist_coeffs_state_set_sample_rate);
 }
 
-static inline void bw_dist_reset_coeffs(bw_dist_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_dist_reset_coeffs(
+		bw_dist_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_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_dist_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_dist_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_dist_reset_state(const bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, float x_0) {
-	bw_hp1_reset_state(&coeffs->hp1_coeffs, &state->hp1_state, x_0); //...
-	bw_peak_reset_state(&coeffs->peak_coeffs, &state->peak_state, 0.f);
-	bw_clip_reset_state(&coeffs->clip_coeffs, &state->clip_state);
-	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_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_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(bw_is_finite(x_0));
+
+	float y = bw_hp1_reset_state(&coeffs->hp1_coeffs, &state->hp1_state, x_0);
+	y = bw_peak_reset_state(&coeffs->peak_coeffs, &state->peak_state, y);
+	y = bw_clip_reset_state(&coeffs->clip_coeffs, &state->clip_state, y);
+	y = bw_satur_reset_state(&coeffs->satur_coeffs, &state->satur_state, y);
+	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_dist_state");
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_dist_update_coeffs_ctrl(bw_dist_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_dist_reset_state_multi(
+		const bw_dist_coeffs * BW_RESTRICT              coeffs,
+		bw_dist_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_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_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_dist_reset_state(coeffs, state[i], x_0[i]);
+	else
+		for (size_t i = 0; i < n_channels; i++)
+			bw_dist_reset_state(coeffs, state[i], x_0[i]);
+
+	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);
+}
+
+static inline void bw_dist_update_coeffs_ctrl(
+		bw_dist_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_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_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_dist_update_coeffs_audio(bw_dist_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_dist_update_coeffs_audio(
+		bw_dist_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_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_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
 }
 
-static inline float bw_dist_process1(const bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, float x) {
+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_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(x));
+
 	float y = bw_hp1_process1(&coeffs->hp1_coeffs, &state->hp1_state, x);
 	y = bw_peak_process1(&coeffs->peak_coeffs, &state->peak_state, y);
 	y = bw_clip_process1_comp(&coeffs->clip_coeffs, &state->clip_state, y);
 	y = bw_satur_process1_comp(&coeffs->satur_coeffs, &state->satur_state, y);
 	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_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_dist_process(bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples) {
+static inline void bw_dist_process(
+		bw_dist_coeffs * BW_RESTRICT coeffs,
+		bw_dist_state * BW_RESTRICT  state,
+		const float *                x,
+		float *                      y,
+		size_t                       n_samples) {
+	BW_ASSERT(coeffs != 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_DEEP(bw_dist_state_is_valid(coeffs, state));
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
 	bw_dist_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_dist_update_coeffs_audio(coeffs);
 		y[i] = bw_dist_process1(coeffs, state, x[i]);
 	}
+
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_dist_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
-static inline void bw_dist_process_multi(bw_dist_coeffs *BW_RESTRICT coeffs, bw_dist_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_dist_process_multi(
+		bw_dist_coeffs * BW_RESTRICT                    coeffs,
+		bw_dist_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_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	bw_dist_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_dist_update_coeffs_audio(coeffs);
 		for (size_t j = 0; j < n_channels; j++)
 			y[j][i] = bw_dist_process1(coeffs, state[j], x[j][i]);
 	}
+
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_dist_set_distortion(bw_dist_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_dist_set_distortion(
+		bw_dist_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_peak_set_peak_gain_dB(&coeffs->peak_coeffs, 60.f * value);
+
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 }
 
-static inline void bw_dist_set_tone(bw_dist_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_dist_set_tone(
+		bw_dist_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_lp1_set_cutoff(&coeffs->lp1_coeffs, 475.f + (20e3f - 475.f) * value * value * value);
+
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
 }
 
-static inline void bw_dist_set_volume(bw_dist_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_dist_set_volume(
+		bw_dist_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != 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));
+	BW_ASSERT(value >= 0.f && value <= 1.f);
+
 	bw_gain_set_gain_lin(&coeffs->gain_coeffs, value * value * value);
+
+	BW_ASSERT_DEEP(bw_dist_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_dist_coeffs_state_init);
+}
+
+static inline char bw_dist_coeffs_is_valid(
+		const bw_dist_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_dist_coeffs"))
+		return 0;
+	if (coeffs->state < bw_dist_coeffs_state_init || coeffs->state > bw_dist_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	return bw_hp1_coeffs_is_valid(&coeffs->hp1_coeffs)
+		&& bw_peak_coeffs_is_valid(&coeffs->peak_coeffs)
+		&& bw_clip_coeffs_is_valid(&coeffs->clip_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_dist_state_is_valid(
+		const bw_dist_coeffs * BW_RESTRICT coeffs,
+		const bw_dist_state * BW_RESTRICT  state) {
+	BW_ASSERT(state != 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)
+		return 0;
+#endif
+
+	(void)coeffs;
+
+	return bw_hp1_state_is_valid(&coeffs->hp1_coeffs, &state->hp1_state)
+		&& bw_peak_state_is_valid(&coeffs->peak_coeffs, &state->peak_state)
+		&& bw_clip_state_is_valid(&coeffs->clip_coeffs, &state->clip_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
@@ -324,22 +653,43 @@ class Dist {
 public:
 	Dist();
 
-	void setSampleRate(float sampleRate);
-	void reset(float x_0 = 0.f);
-	void reset(const float *BW_RESTRICT x_0);
-	void reset(const std::array<float, N_CHANNELS> x_0);
-	void process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples);
-	void process(
-		const std::array<const float *, N_CHANNELS> x,
-		const std::array<float *, N_CHANNELS> y,
-		size_t nSamples);
+	void setSampleRate(
+		float sampleRate);
 
-	void setDistortion(float value);
-	void setTone(float value);
-	void setVolume(float value);
+	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);
+
+	void process(
+		std::array<const float *, N_CHANNELS> x,
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples);
+
+	void setDistortion(
+		float value);
+
+	void setTone(
+		float value);
+
+	void setVolume(
+		float value);
 /*! <<<...
  *  }
  *  ```
@@ -351,9 +701,9 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_dist_coeffs	 coeffs;
-	bw_dist_state	 states[N_CHANNELS];
-	bw_dist_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_dist_coeffs			coeffs;
+	bw_dist_state			states[N_CHANNELS];
+	bw_dist_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -364,57 +714,77 @@ inline Dist<N_CHANNELS>::Dist() {
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::setSampleRate(float sampleRate) {
+inline void Dist<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
 	bw_dist_set_sample_rate(&coeffs, sampleRate);
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::reset(float x_0) {
+inline void Dist<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
 	bw_dist_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_dist_reset_state(&coeffs, states + i, x_0);
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_dist_reset_state(&coeffs, states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_dist_reset_state(&coeffs, states + i, x0);
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::reset(const float *BW_RESTRICT x_0) {
-	bw_dist_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_dist_reset_state(&coeffs, states + i, x_0[i]);
+inline void Dist<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 Dist<N_CHANNELS>::reset(const std::array<float, N_CHANNELS> x_0) {
-	reset(x_0.data());
+inline void Dist<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_dist_reset_coeffs(&coeffs);
+	bw_dist_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void Dist<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 Dist<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_dist_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void Dist<N_CHANNELS>::process(
-		const std::array<const float *, N_CHANNELS> x,
-		const std::array<float *, N_CHANNELS> y,
-		size_t nSamples) {
+		std::array<const float *, N_CHANNELS> x,
+		std::array<float *, N_CHANNELS>       y,
+		size_t                                nSamples) {
 	process(x.data(), y.data(), nSamples);
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::setDistortion(float value) {
+inline void Dist<N_CHANNELS>::setDistortion(
+		float value) {
 	bw_dist_set_distortion(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::setTone(float value) {
+inline void Dist<N_CHANNELS>::setTone(
+		float value) {
 	bw_dist_set_tone(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Dist<N_CHANNELS>::setVolume(float value) {
+inline void Dist<N_CHANNELS>::setVolume(
+		float value) {
 	bw_dist_set_volume(&coeffs, value);
 }
 
diff --git a/include/bw_wah.h b/include/bw_wah.h
index 4d848f7..ce3c6f9 100644
--- a/include/bw_wah.h
+++ b/include/bw_wah.h
@@ -216,8 +216,9 @@ static inline void bw_wah_set_wah(
 	bw_wah_coeffs * BW_RESTRICT coeffs,
 	float                       value);
 /*! <<<```
- *    Sets the wah pedal position to the given `value` in [`0.f` (low cutoff),
- *    `1.f` (high cutoff)] in `coeffs`.
+ *    Sets the wah pedal position to the given `value`.
+ *
+ *    Valid range: [`0.f` (low cutoff), `1.f` (high cutoff)].
  *
  *    Default value: `0.5f`.
  *