From 07ff65597fe6e7c2214fde6e952db3e02de3c26d Mon Sep 17 00:00:00 2001
From: Stefano D'Angelo <s@dangelo.audio>
Date: Fri, 22 Sep 2023 14:52:45 +0200
Subject: [PATCH] finalized bw_comb + examples + better debug in bw_delay

---
 TODO                                      |   1 +
 examples/fx_comb/src/bw_example_fx_comb.c |   2 +-
 examples/fx_comb/vst3/Makefile            |   3 +
 examples/fxpp_comb/vst3/Makefile          |   3 +
 include/bw_comb.h                         | 703 +++++++++++++++++++---
 include/bw_delay.h                        |  54 +-
 6 files changed, 655 insertions(+), 111 deletions(-)

diff --git a/TODO b/TODO
index 82cf7a5..c70e71e 100644
--- a/TODO
+++ b/TODO
@@ -18,6 +18,7 @@ finally:
 * thank scientific paper authors
 * change config.h in examples version 1.0.0
 * "Templates must have C++ linkage"?
+* state that mem_set() can/must be called on uninitialized state (before reset_state)
 
 build system:
 * single header generation (vs modules in bwp... to think about)
diff --git a/examples/fx_comb/src/bw_example_fx_comb.c b/examples/fx_comb/src/bw_example_fx_comb.c
index 4a711ae..544f7fd 100644
--- a/examples/fx_comb/src/bw_example_fx_comb.c
+++ b/examples/fx_comb/src/bw_example_fx_comb.c
@@ -38,7 +38,7 @@ void bw_example_fx_comb_mem_set(bw_example_fx_comb *instance, void *mem) {
 
 void bw_example_fx_comb_reset(bw_example_fx_comb *instance) {
 	bw_comb_reset_coeffs(&instance->comb_coeffs);
-	bw_comb_reset_state(&instance->comb_coeffs, &instance->comb_state);
+	bw_comb_reset_state(&instance->comb_coeffs, &instance->comb_state, 0.f);
 }
 
 void bw_example_fx_comb_process(bw_example_fx_comb *instance, const float** x, float** y, int n_samples) {
diff --git a/examples/fx_comb/vst3/Makefile b/examples/fx_comb/vst3/Makefile
index b72ae23..2a07762 100644
--- a/examples/fx_comb/vst3/Makefile
+++ b/examples/fx_comb/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fx_comb
 SOURCE := bw_example_fx_comb.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_comb/vst3/Makefile b/examples/fxpp_comb/vst3/Makefile
index 9461b0c..f389815 100644
--- a/examples/fxpp_comb/vst3/Makefile
+++ b/examples/fxpp_comb/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_fxpp_comb
 SOURCE := bw_example_fxpp_comb.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_comb.h b/include/bw_comb.h
index e6375ab..5bc4e21 100644
--- a/include/bw_comb.h
+++ b/include/bw_comb.h
@@ -33,7 +33,7 @@
  *    J. Audio Eng. Soc., vol. 45, no. 10, pp. 764-788, October 1997.
  *
  *    Unlike in the original paper, the feedback signal is not subtracted but
- *    rather added to the input. 
+ *    rather added to the input.
  *  }}}
  *  changelog {{{
  *    <ul>
@@ -41,6 +41,10 @@
  *        <ul>
  *          <li>Added initial value argument in
  *              <code>bw_chorus_reset_state()</code>.</li>
+ *          <li>Added <code>bw_comb_reset_state_multi()</code> and updated C++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_comb_reset_state()</code> returns the initial
+ *              output value.</li>
  *          <li>Added overloaded C++ <code>reset()</code> functions taking
  *              arrays as arguments.</li>
  *          <li>Now using <code>size_t</code> instead of
@@ -54,6 +58,8 @@
  *          <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>:
@@ -102,65 +108,113 @@ typedef struct bw_comb_state bw_comb_state;
  *
  *    #### bw_comb_init()
  *  ```>>> */
-static inline void bw_comb_init(bw_comb_coeffs *BW_RESTRICT coeffs, float max_delay);
+static inline void bw_comb_init(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        max_delay);
 /*! <<<```
  *    Initializes input parameter values in `coeffs` using `max_delay` (s) as
  *    the maximum delay time.
  *
+ *    `max_delay` must be finite and non-negative.
+ *
  *    #### bw_comb_set_sample_rate()
  *  ```>>> */
-static inline void bw_comb_set_sample_rate(bw_comb_coeffs *BW_RESTRICT coeffs, float sample_rate);
+static inline void bw_comb_set_sample_rate(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        sample_rate);
 /*! <<<```
  *    Sets the `sample_rate` (Hz) value in `coeffs`.
  *
  *    #### bw_comb_mem_req()
  *  ```>>> */
-static inline size_t bw_comb_mem_req(const bw_comb_coeffs *BW_RESTRICT coeffs);
+static inline size_t bw_comb_mem_req(
+	const bw_comb_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Returns the size, in bytes, of contiguous memory to be supplied to
  *    `bw_comb_mem_set()` using `coeffs`.
  *
  *    #### bw_comb_mem_set()
  *  ```>>> */
-static inline void bw_comb_mem_set(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, void *BW_RESTRICT mem);
+static inline void bw_comb_mem_set(
+	const bw_comb_coeffs * BW_RESTRICT coeffs,
+	bw_comb_state * BW_RESTRICT        state,
+	void * BW_RESTRICT                 mem);
 /*! <<<```
- *    Associates the contiguous memory block `mem` to the given `state`.
+ *    Associates the contiguous memory block `mem` to the given `state` using
+ *    `coeffs`.
  *
  *    #### bw_comb_reset_coeffs()
  *  ```>>> */
-static inline void bw_comb_reset_coeffs(bw_comb_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comb_reset_coeffs(
+	bw_comb_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Resets coefficients in `coeffs` to assume their target values.
  *
  *    #### bw_comb_reset_state()
  *  ```>>> */
-static inline void bw_comb_reset_state(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, float x_0);
+static inline float bw_comb_reset_state(
+	const bw_comb_coeffs * BW_RESTRICT coeffs,
+	bw_comb_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.
+ *
+ *    If parameter `fb`  has value `-1.f` or `1.f`, then `x_0` must be `0.f`.
+ *
+ *    #### bw_comb_reset_state_multi()
+ *  ```>>> */
+static inline void bw_comb_reset_state_multi(
+	const bw_comb_coeffs * BW_RESTRICT              coeffs,
+	bw_comb_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`.
+ *
+ *    If parameter `fb`  has value `-1.f` or `1.f`, then `x_0` must only contain
+ *    `0.f`.
  *
  *    #### bw_comb_update_coeffs_ctrl()
  *  ```>>> */
-static inline void bw_comb_update_coeffs_ctrl(bw_comb_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comb_update_coeffs_ctrl(
+	bw_comb_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers control-rate update of coefficients in `coeffs`.
  *
  *    #### bw_comb_update_coeffs_audio()
  *  ```>>> */
-static inline void bw_comb_update_coeffs_audio(bw_comb_coeffs *BW_RESTRICT coeffs);
+static inline void bw_comb_update_coeffs_audio(
+	bw_comb_coeffs * BW_RESTRICT coeffs);
 /*! <<<```
  *    Triggers audio-rate update of coefficients in `coeffs`.
  *
  *    #### bw_comb_process1()
  *  ```>>> */
-static inline float bw_comb_process1(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, float x);
+static inline float bw_comb_process1(
+	const bw_comb_coeffs * BW_RESTRICT coeffs,
+	bw_comb_state * BW_RESTRICT        state,
+	float                              x);
 /*! <<<```
  *    Processes one input sample `x` using `coeffs`, while using and updating
  *    `state`. Returns the corresponding output sample.
  *
  *    #### bw_comb_process()
  *  ```>>> */
-static inline void bw_comb_process(bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples);
+static inline void bw_comb_process(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	bw_comb_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
@@ -168,7 +222,13 @@ static inline void bw_comb_process(bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_s
  *
  *    #### bw_comb_process_multi()
  *  ```>>> */
-static inline void bw_comb_process_multi(bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_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_comb_process_multi(
+	bw_comb_coeffs * BW_RESTRICT                    coeffs,
+	bw_comb_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
@@ -177,43 +237,95 @@ static inline void bw_comb_process_multi(bw_comb_coeffs *BW_RESTRICT coeffs, bw_
  *
  *    #### bw_comb_set_delay_ff()
  *  ```>>> */
-static inline void bw_comb_set_delay_ff(bw_comb_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comb_set_delay_ff(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the feedforward delay time `value` (s) in `coeffs`.
  *
+ *    This parameter is internally limited to avoid buffer overflows.
+ *
+ *    `value` must be finite.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comb_set_delay_fb()
  *  ```>>> */
-static inline void bw_comb_set_delay_fb(bw_comb_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comb_set_delay_fb(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the feedback delay time `value` (s) in `coeffs`.
  *
+ *    This parameter is internally limited to avoid buffer overflows.
+ *
+ *    `value` must be finite.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comb_set_coeff_blend()
  *  ```>>> */
-static inline void bw_comb_set_coeff_blend(bw_comb_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comb_set_coeff_blend(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the blend coefficient `value` in `coeffs`.
  *
+ *    `value` must be finite.
+ *
  *    Default value: `1.f`.
  *
  *    #### bw_comb_set_coeff_ff()
  *  ```>>> */
-static inline void bw_comb_set_coeff_ff(bw_comb_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comb_set_coeff_ff(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the feedforward coefficient `value` in `coeffs`.
  *
+ *    `value` must be finite.
+ *
  *    Default value: `0.f`.
  *
  *    #### bw_comb_set_coeff_fb()
  *  ```>>> */
-static inline void bw_comb_set_coeff_fb(bw_comb_coeffs *BW_RESTRICT coeffs, float value);
+static inline void bw_comb_set_coeff_fb(
+	bw_comb_coeffs * BW_RESTRICT coeffs,
+	float                        value);
 /*! <<<```
  *    Sets the feedback coefficient `value` in `coeffs`.
  *
+ *    Valid range: [`-1.f`, `1.f`].
+ *
  *    Default value: `0.f`.
+ *
+ *    #### bw_comb_coeffs_is_valid()
+ *  ```>>> */
+static inline char bw_comb_coeffs_is_valid(
+	const bw_comb_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_comb_coeffs`.
+ *
+ *    #### bw_comb_state_is_valid()
+ *  ```>>> */
+static inline char bw_comb_state_is_valid(
+	const bw_comb_coeffs * BW_RESTRICT coeffs,
+	const bw_comb_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_comb_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -234,35 +346,70 @@ static inline void bw_comb_set_coeff_fb(bw_comb_coeffs *BW_RESTRICT coeffs, floa
 extern "C" {
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_comb_coeffs_state {
+	bw_comb_coeffs_state_invalid,
+	bw_comb_coeffs_state_init,
+	bw_comb_coeffs_state_set_sample_rate,
+	bw_comb_coeffs_state_reset_coeffs
+};
+#endif
+
+#ifdef BW_DEBUG_DEEP
+enum bw_comb_state_state {
+	bw_comb_state_state_invalid,
+	bw_comb_state_state_mem_set,
+	bw_comb_state_state_reset_state
+};
+#endif
+
 struct bw_comb_coeffs {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_comb_coeffs_state	state;
+	uint32_t			reset_id;
+#endif
+
 	// Sub-components
-	bw_delay_coeffs		delay_coeffs;
-	bw_gain_coeffs		blend_coeffs;
-	bw_gain_coeffs		ff_coeffs;
-	bw_gain_coeffs		fb_coeffs;
-	bw_one_pole_coeffs	smooth_coeffs;
-	bw_one_pole_state	smooth_delay_ff_state;
-	bw_one_pole_state	smooth_delay_fb_state;
+	bw_delay_coeffs			delay_coeffs;
+	bw_gain_coeffs			blend_coeffs;
+	bw_gain_coeffs			ff_coeffs;
+	bw_gain_coeffs			fb_coeffs;
+	bw_one_pole_coeffs		smooth_coeffs;
+	bw_one_pole_state		smooth_delay_ff_state;
+	bw_one_pole_state		smooth_delay_fb_state;
 
 	// Coefficients
-	float			fs;
+	float				fs;
 
-	size_t			dffi;
-	float			dfff;
-	size_t			dfbi;
-	float			dfbf;
+	size_t				dffi;
+	float				dfff;
+	size_t				dfbi;
+	float				dfbf;
 
 	// Parameters
-	float			delay_ff;
-	float			delay_fb;
+	float				delay_ff;
+	float				delay_fb;
 };
 
 struct bw_comb_state {
+#ifdef BW_DEBUG_DEEP
+	uint32_t			hash;
+	enum bw_comb_state_state	state;
+	uint32_t			coeffs_reset_id;
+#endif
+
 	// Sub-components
-	bw_delay_state		delay_state;
+	bw_delay_state			delay_state;
 };
 
-static inline void bw_comb_init(bw_comb_coeffs *BW_RESTRICT coeffs, float max_delay) {
+static inline void bw_comb_init(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        max_delay) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT(bw_is_finite(max_delay));
+	BW_ASSERT(max_delay >= 0.f);
+
 	bw_delay_init(&coeffs->delay_coeffs, max_delay);
 	bw_gain_init(&coeffs->blend_coeffs);
 	bw_gain_init(&coeffs->ff_coeffs);
@@ -274,27 +421,73 @@ static inline void bw_comb_init(bw_comb_coeffs *BW_RESTRICT coeffs, float max_de
 	bw_gain_set_gain_lin(&coeffs->fb_coeffs, 0.f);
 	coeffs->delay_ff = 0.f;
 	coeffs->delay_fb = 0.f;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->hash = bw_hash_sdbm("bw_comb_coeffs");
+	coeffs->state = bw_comb_coeffs_state_init;
+	coeffs->reset_id = coeffs->hash + 1;
+#endif
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comb_coeffs_state_init);
 }
 
-static inline void bw_comb_set_sample_rate(bw_comb_coeffs *BW_RESTRICT coeffs, float sample_rate) {
+static inline void bw_comb_set_sample_rate(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        sample_rate) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(sample_rate) && sample_rate > 0.f);
+
 	bw_delay_set_sample_rate(&coeffs->delay_coeffs, sample_rate);
-	bw_gain_set_sample_rate(&coeffs->blend_coeffs, sample_rate); 
-	bw_gain_set_sample_rate(&coeffs->ff_coeffs, sample_rate); 
-	bw_gain_set_sample_rate(&coeffs->fb_coeffs, sample_rate); 
+	bw_gain_set_sample_rate(&coeffs->blend_coeffs, sample_rate);
+	bw_gain_set_sample_rate(&coeffs->ff_coeffs, sample_rate);
+	bw_gain_set_sample_rate(&coeffs->fb_coeffs, sample_rate);
 	bw_one_pole_set_sample_rate(&coeffs->smooth_coeffs, sample_rate);
 	bw_one_pole_reset_coeffs(&coeffs->smooth_coeffs);
 	coeffs->fs = sample_rate;
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_comb_coeffs_state_set_sample_rate;
+#endif
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comb_coeffs_state_set_sample_rate);
 }
 
-static inline size_t bw_comb_mem_req(const bw_comb_coeffs *BW_RESTRICT coeffs) {
+static inline size_t bw_comb_mem_req(
+		const bw_comb_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
+
 	return bw_delay_mem_req(&coeffs->delay_coeffs);
 }
 
-static inline void bw_comb_mem_set(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, void *BW_RESTRICT mem) {
+static inline void bw_comb_mem_set(
+		const bw_comb_coeffs * BW_RESTRICT coeffs,
+		bw_comb_state * BW_RESTRICT        state,
+		void * BW_RESTRICT                 mem) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(mem != NULL);
+
 	bw_delay_mem_set(&coeffs->delay_coeffs, &state->delay_state, mem);
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_comb_state");
+	state->state = bw_comb_state_state_mem_set;
+#endif
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state == bw_comb_state_state_mem_set);
 }
 
-static inline void bw_comb_do_update_coeffs(bw_comb_coeffs *BW_RESTRICT coeffs, char force) {
+static inline void bw_comb_do_update_coeffs(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		char                         force) {
 	float delay_ff_cur = bw_one_pole_get_y_z1(&coeffs->smooth_delay_ff_state);
 	float delay_fb_cur = bw_one_pole_get_y_z1(&coeffs->smooth_delay_fb_state);
 	if (force || delay_ff_cur != coeffs->delay_ff) {
@@ -323,7 +516,12 @@ static inline void bw_comb_do_update_coeffs(bw_comb_coeffs *BW_RESTRICT coeffs,
 	}
 }
 
-static inline void bw_comb_reset_coeffs(bw_comb_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_comb_reset_coeffs(
+		bw_comb_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_set_sample_rate);
+
 	bw_delay_reset_coeffs(&coeffs->delay_coeffs);
 	bw_gain_reset_coeffs(&coeffs->blend_coeffs);
 	bw_gain_reset_coeffs(&coeffs->ff_coeffs);
@@ -331,68 +529,323 @@ static inline void bw_comb_reset_coeffs(bw_comb_coeffs *BW_RESTRICT coeffs) {
 	bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_delay_ff_state, coeffs->delay_ff);
 	bw_one_pole_reset_state(&coeffs->smooth_coeffs, &coeffs->smooth_delay_fb_state, coeffs->delay_fb);
 	bw_comb_do_update_coeffs(coeffs, 1);
+
+#ifdef BW_DEBUG_DEEP
+	coeffs->state = bw_comb_coeffs_state_reset_coeffs;
+	coeffs->reset_id++;
+#endif
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state == bw_comb_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_comb_reset_state(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, float x_0) {
-	bw_delay_reset_state(&coeffs->delay_coeffs, &state->delay_state, x_0);
+static inline float bw_comb_reset_state(
+		const bw_comb_coeffs * BW_RESTRICT coeffs,
+		bw_comb_state * BW_RESTRICT        state,
+		float                              x_0) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_mem_set);
+	BW_ASSERT(bw_is_finite(x_0));
+	BW_ASSERT(bw_gain_get_gain_cur(&coeffs->fb_coeffs) == -1.f || bw_gain_get_gain_cur(&coeffs->fb_coeffs) == 1.f ? x_0 == 0.f : 1);
+
+	const float fb = bw_gain_get_gain_cur(&coeffs->fb_coeffs);
+	float y;
+	if (fb == -1.f || fb == 1.f) {
+		bw_delay_reset_state(&coeffs->delay_coeffs, &state->delay_state, 0.f);
+		y = 0.f;
+	} else {
+		const float v = x_0 / (1.f - fb);
+		bw_delay_reset_state(&coeffs->delay_coeffs, &state->delay_state, v);
+		y = (bw_gain_get_gain_cur(&coeffs->ff_coeffs) + bw_gain_get_gain_cur(&coeffs->blend_coeffs)) * v;
+	}
+
+#ifdef BW_DEBUG_DEEP
+	state->state = bw_comb_state_state_reset_state;
+	state->coeffs_reset_id = coeffs->reset_id;
+#endif
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_comb_update_coeffs_ctrl(bw_comb_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_comb_reset_state_multi(
+		const bw_comb_coeffs * BW_RESTRICT              coeffs,
+		bw_comb_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_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_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_comb_reset_state(coeffs, state[i], x_0[i]);
+	else
+		for (size_t i = 0; i < n_channels; i++)
+			bw_comb_reset_state(coeffs, state[i], x_0[i]);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
+}
+
+static inline void bw_comb_update_coeffs_ctrl(
+		bw_comb_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+
 	bw_gain_update_coeffs_ctrl(&coeffs->blend_coeffs);
 	bw_gain_update_coeffs_ctrl(&coeffs->ff_coeffs);
 	bw_gain_update_coeffs_ctrl(&coeffs->fb_coeffs);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_comb_update_coeffs_audio(bw_comb_coeffs *BW_RESTRICT coeffs) {
+static inline void bw_comb_update_coeffs_audio(
+		bw_comb_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+
 	bw_gain_update_coeffs_audio(&coeffs->blend_coeffs);
 	bw_gain_update_coeffs_audio(&coeffs->ff_coeffs);
 	bw_gain_update_coeffs_audio(&coeffs->fb_coeffs);
 	bw_comb_do_update_coeffs(coeffs, 0);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
 }
 
-static inline float bw_comb_process1(const bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, float x) {
+static inline float bw_comb_process1(
+		const bw_comb_coeffs * BW_RESTRICT coeffs,
+		bw_comb_state * BW_RESTRICT        state,
+		float                              x) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
+	BW_ASSERT(bw_is_finite(x));
+
 	const float fb = bw_delay_read(&coeffs->delay_coeffs, &state->delay_state, coeffs->dfbi, coeffs->dfbf);
 	const float v = x + bw_gain_process1(&coeffs->fb_coeffs, fb);
 	bw_delay_write(&coeffs->delay_coeffs, &state->delay_state, v);
 	const float ff = bw_delay_read(&coeffs->delay_coeffs, &state->delay_state, coeffs->dffi, coeffs->dfff);
-	return bw_gain_process1(&coeffs->blend_coeffs, v) + bw_gain_process1(&coeffs->ff_coeffs, ff);
+	const float y = bw_gain_process1(&coeffs->blend_coeffs, v) + bw_gain_process1(&coeffs->ff_coeffs, ff);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
 }
 
-static inline void bw_comb_process(bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples) {
+static inline void bw_comb_process(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		bw_comb_state * BW_RESTRICT  state,
+		const float *                x,
+		float *                      y,
+		size_t                       n_samples) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
 	bw_comb_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_comb_update_coeffs_audio(coeffs);
 		y[i] = bw_comb_process1(coeffs, state, x[i]);
 	}
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT_DEEP(bw_comb_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_comb_state_state_reset_state);
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
-static inline void bw_comb_process_multi(bw_comb_coeffs *BW_RESTRICT coeffs, bw_comb_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_comb_process_multi(
+		bw_comb_coeffs * BW_RESTRICT                    coeffs,
+		bw_comb_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_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	bw_comb_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
 		bw_comb_update_coeffs_audio(coeffs);
 		for (size_t j = 0; j < n_channels; j++)
 			y[j][i] = bw_comb_process1(coeffs, state[j], x[j][i]);
 	}
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_reset_coeffs);
 }
 
-static inline void bw_comb_set_delay_ff(bw_comb_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_comb_set_delay_ff(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+
 	coeffs->delay_ff = value;
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 }
 
-static inline void bw_comb_set_delay_fb(bw_comb_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_comb_set_delay_fb(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+
 	coeffs->delay_fb = value;
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 }
 
-static inline void bw_comb_set_coeff_blend(bw_comb_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_comb_set_coeff_blend(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+
 	bw_gain_set_gain_lin(&coeffs->blend_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 }
 
-static inline void bw_comb_set_coeff_ff(bw_comb_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_comb_set_coeff_ff(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+
 	bw_gain_set_gain_lin(&coeffs->ff_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
 }
 
-static inline void bw_comb_set_coeff_fb(bw_comb_coeffs *BW_RESTRICT coeffs, float value) {
+static inline void bw_comb_set_coeff_fb(
+		bw_comb_coeffs * BW_RESTRICT coeffs,
+		float                        value) {
+	BW_ASSERT(coeffs != NULL);
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+	BW_ASSERT(bw_is_finite(value));
+	BW_ASSERT(value >= -1.f && value <= 1.f);
+
 	bw_gain_set_gain_lin(&coeffs->fb_coeffs, value);
+
+	BW_ASSERT_DEEP(bw_comb_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_comb_coeffs_state_init);
+}
+
+static inline char bw_comb_coeffs_is_valid(
+		const bw_comb_coeffs * BW_RESTRICT coeffs) {
+	BW_ASSERT(coeffs != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->hash != bw_hash_sdbm("bw_comb_coeffs"))
+		return 0;
+	if (coeffs->state < bw_comb_coeffs_state_init || coeffs->state > bw_comb_coeffs_state_reset_coeffs)
+		return 0;
+#endif
+
+	if (!bw_is_finite(coeffs->delay_ff))
+		return 0;
+	if (!bw_is_finite(coeffs->delay_fb))
+		return 0;
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->state >= bw_comb_coeffs_state_set_sample_rate && (!bw_is_finite(coeffs->fs) || coeffs->fs <= 0.f))
+		return 0;
+#endif
+
+	if (!bw_delay_coeffs_is_valid(&coeffs->delay_coeffs)
+		|| !bw_one_pole_coeffs_is_valid(&coeffs->smooth_coeffs))
+		return 0;
+
+#ifdef BW_DEBUG_DEEP
+	if (coeffs->state >= bw_comb_coeffs_state_reset_coeffs) {
+		const size_t len = bw_delay_get_length(&coeffs->delay_coeffs);
+
+		if (!bw_is_finite(coeffs->dfff) || coeffs->dfff < 0.f || coeffs->dfff >= 1.f)
+			return 0;
+		if (coeffs->dffi + coeffs->dfff > len)
+			return 0;
+
+		if (!bw_is_finite(coeffs->dfbf) || coeffs->dfbf < 0.f || coeffs->dfbf >= 1.f)
+			return 0;
+		if (coeffs->dfbi + coeffs->dfbf > len)
+			return 0;
+
+		if (!bw_one_pole_state_is_valid(&coeffs->smooth_coeffs, &coeffs->smooth_delay_ff_state)
+			|| !bw_one_pole_state_is_valid(&coeffs->smooth_coeffs, &coeffs->smooth_delay_fb_state))
+			return 0;
+	}
+#endif
+
+	return bw_gain_coeffs_is_valid(&coeffs->blend_coeffs)
+		&& bw_gain_coeffs_is_valid(&coeffs->ff_coeffs)
+		&& bw_gain_coeffs_is_valid(&coeffs->fb_coeffs);
+}
+
+static inline char bw_comb_state_is_valid(
+		const bw_comb_coeffs * BW_RESTRICT coeffs,
+		const bw_comb_state * BW_RESTRICT  state) {
+	BW_ASSERT(state != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (state->hash != bw_hash_sdbm("bw_comb_state"))
+		return 0;
+	if (state->state < bw_comb_state_state_mem_set || state->state > bw_comb_state_state_reset_state)
+		return 0;
+
+	if (state->state >= bw_comb_state_state_reset_state && coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+		return 0;
+#endif
+
+	return bw_delay_state_is_valid(coeffs ? &coeffs->delay_coeffs : NULL, &state->delay_state);
 }
 
 #ifdef __cplusplus
@@ -410,27 +863,54 @@ namespace Brickworks {
 template<size_t N_CHANNELS>
 class Comb {
 public:
-	Comb(float maxDelay = 1.f);
+	Comb(
+		float maxDelay = 1.f);
+
 	~Comb();
 
-	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 setDelayFF(float value);
-	void setDelayFB(float value);
-	void setCoeffBlend(float value);
-	void setCoeffFF(float value);
-	void setCoeffFB(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 setDelayFF(
+		float value);
+
+	void setDelayFB(
+		float value);
+
+	void setCoeffBlend(
+		float value);
+
+	void setCoeffFF(
+		float value);
+
+	void setCoeffFB(
+		float value);
 /*! <<<...
  *  }
  *  ```
@@ -442,14 +922,15 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_comb_coeffs	 coeffs;
-	bw_comb_state	 states[N_CHANNELS];
-	bw_comb_state	*BW_RESTRICT statesP[N_CHANNELS];
-	void		*BW_RESTRICT mem;
+	bw_comb_coeffs			coeffs;
+	bw_comb_state			states[N_CHANNELS];
+	bw_comb_state * BW_RESTRICT	statesP[N_CHANNELS];
+	void * BW_RESTRICT		mem;
 };
 
 template<size_t N_CHANNELS>
-inline Comb<N_CHANNELS>::Comb(float maxDelay) {
+inline Comb<N_CHANNELS>::Comb(
+		float maxDelay) {
 	bw_comb_init(&coeffs, maxDelay);
 	for (size_t i = 0; i < N_CHANNELS; i++)
 		statesP[i] = states + i;
@@ -463,7 +944,8 @@ inline Comb<N_CHANNELS>::~Comb() {
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::setSampleRate(float sampleRate) {
+inline void Comb<N_CHANNELS>::setSampleRate(
+		float sampleRate) {
 	bw_comb_set_sample_rate(&coeffs, sampleRate);
 	size_t req = bw_comb_mem_req(&coeffs);
 	if (mem != nullptr)
@@ -475,62 +957,83 @@ inline void Comb<N_CHANNELS>::setSampleRate(float sampleRate) {
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::reset(float x_0) {
+inline void Comb<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
 	bw_comb_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_comb_reset_state(&coeffs, states + i, x_0);
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_comb_reset_state(&coeffs, states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_comb_reset_state(&coeffs, states + i, x0);
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::reset(const float *BW_RESTRICT x_0) {
-	bw_comb_reset_coeffs(&coeffs);
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_comb_reset_state(&coeffs, states + i, x_0[i]);
+inline void Comb<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 Comb<N_CHANNELS>::reset(const std::array<float, N_CHANNELS> x_0) {
-	reset(x_0.data());
+inline void Comb<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_comb_reset_coeffs(&coeffs);
+	bw_comb_reset_state_multi(&coeffs, statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void Comb<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 Comb<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_comb_process_multi(&coeffs, statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void Comb<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 Comb<N_CHANNELS>::setDelayFF(float value) {
+inline void Comb<N_CHANNELS>::setDelayFF(
+		float value) {
 	bw_comb_set_delay_ff(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::setDelayFB(float value) {
+inline void Comb<N_CHANNELS>::setDelayFB(
+		float value) {
 	bw_comb_set_delay_fb(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::setCoeffBlend(float value) {
+inline void Comb<N_CHANNELS>::setCoeffBlend(
+		float value) {
 	bw_comb_set_coeff_blend(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::setCoeffFF(float value) {
+inline void Comb<N_CHANNELS>::setCoeffFF(
+		float value) {
 	bw_comb_set_coeff_ff(&coeffs, value);
 }
 
 template<size_t N_CHANNELS>
-inline void Comb<N_CHANNELS>::setCoeffFB(float value) {
+inline void Comb<N_CHANNELS>::setCoeffFB(
+		float value) {
 	bw_comb_set_coeff_fb(&coeffs, value);
 }
 
diff --git a/include/bw_delay.h b/include/bw_delay.h
index a4a5cbb..9a4a591 100644
--- a/include/bw_delay.h
+++ b/include/bw_delay.h
@@ -135,7 +135,8 @@ static inline void bw_delay_mem_set(
 	bw_delay_state * BW_RESTRICT        state,
 	void * BW_RESTRICT                  mem);
 /*! <<<```
- *    Associates the contiguous memory block `mem` to the given `state`.
+ *    Associates the contiguous memory block `mem` to the given `state` using
+ *    `coeffs`.
  *
  *    #### bw_delay_reset_coeffs()
  *  ```>>> */
@@ -321,6 +322,14 @@ enum bw_delay_coeffs_state {
 };
 #endif
 
+#ifdef BW_DEBUG_DEEP
+enum bw_delay_state_state {
+	bw_delay_state_state_invalid,
+	bw_delay_state_state_mem_set,
+	bw_delay_state_state_reset_state
+};
+#endif
+
 struct bw_delay_coeffs {
 #ifdef BW_DEBUG_DEEP
 	uint32_t			hash;
@@ -343,13 +352,14 @@ struct bw_delay_coeffs {
 
 struct bw_delay_state {
 #ifdef BW_DEBUG_DEEP
-	uint32_t		hash;
-	uint32_t		coeffs_reset_id;
+	uint32_t			hash;
+	enum bw_delay_state_state	state;
+	uint32_t			coeffs_reset_id;
 #endif
 
 	// States
-	float * BW_RESTRICT	buf;
-	size_t			idx;
+	float * BW_RESTRICT		buf;
+	size_t				idx;
 };
 
 static inline void bw_delay_init(
@@ -410,6 +420,15 @@ static inline void bw_delay_mem_set(
 
 	(void)coeffs;
 	state->buf = (float *)mem;
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_delay_state");
+	state->state = bw_delay_state_state_mem_set;
+#endif
+	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
+	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_set_sample_rate);
+	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state == bw_delay_state_state_mem_set);
 }
 
 static inline void bw_delay_do_update_coeffs_ctrl(bw_delay_coeffs *BW_RESTRICT coeffs) {
@@ -446,6 +465,8 @@ static inline float bw_delay_reset_state(
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_mem_set);
 	BW_ASSERT(bw_is_finite(x_0));
 
 	bw_buf_fill(x_0, state->buf, coeffs->len);
@@ -453,12 +474,13 @@ static inline float bw_delay_reset_state(
 	const float y = x_0;
 
 #ifdef BW_DEBUG_DEEP
-	state->hash = bw_hash_sdbm("bw_delay_state");
+	state->state = bw_delay_state_state_reset_state;
 	state->coeffs_reset_id = coeffs->reset_id;
 #endif
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(y));
 
 	return y;
@@ -498,6 +520,7 @@ static float bw_delay_read(
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT(state != NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(df));
 	BW_ASSERT(df >= 0.f && df < 1.f);
 	BW_ASSERT(di + df <= coeffs->len);
@@ -509,6 +532,7 @@ static float bw_delay_read(
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(y));
 
 	return y;
@@ -523,6 +547,7 @@ static void bw_delay_write(
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT(state != NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
 
 	state->idx++;
@@ -532,6 +557,7 @@ static void bw_delay_write(
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 }
 
 static inline void bw_delay_update_coeffs_ctrl(
@@ -564,6 +590,7 @@ static inline float bw_delay_process1(
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT(state != NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(x));
 
 	bw_delay_write(coeffs, state, x);
@@ -572,6 +599,7 @@ static inline float bw_delay_process1(
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(bw_is_finite(y));
 
 	return y;
@@ -588,6 +616,7 @@ static inline void bw_delay_process(
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT(state != NULL);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT(x != NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
 	BW_ASSERT(y != NULL);
@@ -599,6 +628,7 @@ static inline void bw_delay_process(
 	BW_ASSERT_DEEP(bw_delay_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_delay_coeffs_state_reset_coeffs);
 	BW_ASSERT_DEEP(bw_delay_state_is_valid(coeffs, state));
+	BW_ASSERT_DEEP(state->state >= bw_delay_state_state_reset_state);
 	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
 }
 
@@ -694,8 +724,7 @@ static inline char bw_delay_state_is_valid(
 #ifdef BW_DEBUG_DEEP
 	if (state->hash != bw_hash_sdbm("bw_delay_state"))
 		return 0;
-
-	if (coeffs != NULL && coeffs->reset_id != state->coeffs_reset_id)
+	if (state->state < bw_delay_state_state_mem_set || state->state > bw_delay_state_state_reset_state)
 		return 0;
 #endif
 
@@ -705,8 +734,13 @@ static inline char bw_delay_state_is_valid(
 		return 0;
 
 #ifdef BW_DEBUG_DEEP
-	if (coeffs != NULL && coeffs->state >= bw_delay_coeffs_state_set_sample_rate && state->idx >= coeffs->len)
-		return 0;
+	if (state->state >= bw_delay_state_state_reset_state && coeffs != NULL) {
+		if (coeffs->reset_id != state->coeffs_reset_id)
+			return 0;
+
+		if (state->idx >= coeffs->len)
+			return 0;
+	}
 #endif
 
 	return 1;