diff --git a/examples/synth_mono/src/bw_example_synth_mono.c b/examples/synth_mono/src/bw_example_synth_mono.c
index 0dbabe7..eb0ec0a 100644
--- a/examples/synth_mono/src/bw_example_synth_mono.c
+++ b/examples/synth_mono/src/bw_example_synth_mono.c
@@ -87,35 +87,37 @@ void bw_example_synth_mono_reset(bw_example_synth_mono *instance) {
 	const float cutoff = 20.f + (20e3f - 20.f) * v * v * v;
 	bw_svf_set_cutoff(&instance->vcf_coeffs, bw_clipf(cutoff, 20.f, 20e3f));
 	
+	float p, pi;
 	bw_phase_gen_reset_coeffs(&instance->vco1_phase_gen_coeffs);
-	bw_phase_gen_reset_state(&instance->vco1_phase_gen_coeffs, &instance->vco1_phase_gen_state, 0.f);
+	bw_phase_gen_reset_state(&instance->vco1_phase_gen_coeffs, &instance->vco1_phase_gen_state, 0.f, &p, &pi);
 	bw_osc_pulse_reset_coeffs(&instance->vco1_pulse_coeffs);
 	bw_osc_tri_reset_coeffs(&instance->vco1_tri_coeffs);
 	bw_gain_reset_coeffs(&instance->vco1_gain_coeffs);
 	bw_phase_gen_reset_coeffs(&instance->vco2_phase_gen_coeffs);
-	bw_phase_gen_reset_state(&instance->vco2_phase_gen_coeffs, &instance->vco2_phase_gen_state, 0.f);
+	bw_phase_gen_reset_state(&instance->vco2_phase_gen_coeffs, &instance->vco2_phase_gen_state, 0.f, &p, &pi);
 	bw_osc_pulse_reset_coeffs(&instance->vco2_pulse_coeffs);
 	bw_osc_tri_reset_coeffs(&instance->vco2_tri_coeffs);
 	bw_gain_reset_coeffs(&instance->vco2_gain_coeffs);
 	bw_phase_gen_reset_coeffs(&instance->vco3_phase_gen_coeffs);
-	bw_phase_gen_reset_state(&instance->vco3_phase_gen_coeffs, &instance->vco3_phase_gen_state, 0.f);
+	bw_phase_gen_reset_state(&instance->vco3_phase_gen_coeffs, &instance->vco3_phase_gen_state, 0.f, &p, &pi);
 	bw_osc_pulse_reset_coeffs(&instance->vco3_pulse_coeffs);
 	bw_osc_tri_reset_coeffs(&instance->vco3_tri_coeffs);
 	bw_gain_reset_coeffs(&instance->vco3_gain_coeffs);
-	bw_osc_filt_reset_state(&instance->osc_filt_state);
+	bw_osc_filt_reset_state(&instance->osc_filt_state, 0.f);
 	bw_pink_filt_reset_state(&instance->pink_filt_coeffs, &instance->pink_filt_state);
 	bw_gain_reset_coeffs(&instance->noise_gain_coeffs);
 	bw_env_gen_reset_coeffs(&instance->vcf_env_gen_coeffs);
-	bw_env_gen_reset_state(&instance->vcf_env_gen_coeffs, &instance->vcf_env_gen_state);
+	bw_env_gen_reset_state(&instance->vcf_env_gen_coeffs, &instance->vcf_env_gen_state, 0);
 	bw_svf_reset_coeffs(&instance->vcf_coeffs);
-	bw_svf_reset_state(&instance->vcf_coeffs, &instance->vcf_state, 0.f);
+	float lp, bp, hp;
+	bw_svf_reset_state(&instance->vcf_coeffs, &instance->vcf_state, 0.f, &lp, &bp, &hp);
 	bw_env_gen_reset_coeffs(&instance->vca_env_gen_coeffs);
-	bw_env_gen_reset_state(&instance->vca_env_gen_coeffs, &instance->vca_env_gen_state);
+	bw_env_gen_reset_state(&instance->vca_env_gen_coeffs, &instance->vca_env_gen_state, 0);
 	bw_phase_gen_reset_coeffs(&instance->a440_phase_gen_coeffs);
-	bw_phase_gen_reset_state(&instance->a440_phase_gen_coeffs, &instance->a440_phase_gen_state, 0.f);
+	bw_phase_gen_reset_state(&instance->a440_phase_gen_coeffs, &instance->a440_phase_gen_state, 0.f, &p, &pi);
 	bw_gain_reset_coeffs(&instance->gain_coeffs);
 	bw_ppm_reset_coeffs(&instance->ppm_coeffs);
-	bw_ppm_reset_state(&instance->ppm_coeffs, &instance->ppm_state);
+	bw_ppm_reset_state(&instance->ppm_coeffs, &instance->ppm_state, 0.f);
 	instance->note = 60;
 	instance->gate = 0;
 	instance->pitch_bend = 0.f;
diff --git a/examples/synth_mono/vst3/Makefile b/examples/synth_mono/vst3/Makefile
index 4296ac9..5fa53d4 100644
--- a/examples/synth_mono/vst3/Makefile
+++ b/examples/synth_mono/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_synth_mono
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_synth_mono.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/synthpp_mono/vst3/Makefile b/examples/synthpp_mono/vst3/Makefile
index f4146f5..fdc83a1 100644
--- a/examples/synthpp_mono/vst3/Makefile
+++ b/examples/synthpp_mono/vst3/Makefile
@@ -4,3 +4,6 @@ NAME := bw_example_synthpp_mono
 SOURCES = ${SOURCES_COMMON} ${ROOT_DIR}/../src/bw_example_synthpp_mono.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_osc_filt.h b/include/bw_osc_filt.h
index 8fb5de4..d67a031 100644
--- a/include/bw_osc_filt.h
+++ b/include/bw_osc_filt.h
@@ -35,6 +35,14 @@
  *    <ul>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
+ *          <li>Added initial input value to
+ *              <code>bw_osc_filt_reset_state()</code>.</li>
+ *          <li>Added <code>bw_osc_filt_reset_state_multi()</code> and updated C++
+ *              API in this regard.</li>
+ *          <li>Now <code>bw_osc_filt_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_osc_filt_process()</code> and
  *              <code>bw_osc_filt_process_multi()</code> now use
  *              <code>size_t</code> to count samples and channels.</li>
@@ -44,6 +52,7 @@
  *          <li>Added overloaded C++ <code>process()</code> function taking
  *              C-style arrays as arguments.</li>
  *          <li>Removed usage of reserved identifiers.</li>
+ *          <li>Added debugging code.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>0.6.0</strong>:
@@ -89,20 +98,45 @@ typedef struct bw_osc_filt_state bw_osc_filt_state;
  *
  *    #### bw_osc_filt_reset()
  *  ```>>> */
-static inline void bw_osc_filt_reset_state(bw_osc_filt_state *BW_RESTRICT state);
+static inline float bw_osc_filt_reset_state(
+	bw_osc_filt_state * BW_RESTRICT state,
+	float                           x_0);
 /*! <<<```
- *    Resets the given `state` to its initial values.
+ *    Resets the given `state` to its initial values using the given initial
+ *    input value `x_0`.
+ *
+ *    Returns the corresponding initial output value.
+ *
+ *    #### bw_osc_filt_reset_state_multi()
+ *  ```>>> */
+static inline void bw_osc_filt_reset_state_multi(
+	bw_osc_filt_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
+ *    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_osc_filt_process1()
  *  ```>>> */
-static inline float bw_osc_filt_process1(bw_osc_filt_state *BW_RESTRICT state, float x);
+static inline float bw_osc_filt_process1(
+	bw_osc_filt_state * BW_RESTRICT state,
+	float                           x);
 /*! <<<```
- *    Processes one input sample `x` usign and updating `state`. Returns the
+ *    Processes one input sample `x` using and updating `state`. Returns the
  *    corresponding output sample.
  *
  *    #### bw_osc_filt_process()
  *  ```>>> */
-static inline void bw_osc_filt_process(bw_osc_filt_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples);
+static inline void bw_osc_filt_process(
+	bw_osc_filt_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
@@ -110,11 +144,28 @@ static inline void bw_osc_filt_process(bw_osc_filt_state *BW_RESTRICT state, con
  *
  *    #### bw_osc_filt_process_multi()
  *  ```>>> */
-static inline void bw_osc_filt_process_multi(bw_osc_filt_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_osc_filt_process_multi(
+	bw_osc_filt_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
  *    using and updating each of the `n_channels` `state`s.
+ *
+ *    #### bw_osc_filt_state_is_valid()
+ *  ```>>> */
+static inline char bw_osc_filt_state_is_valid(
+	const bw_osc_filt_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.
+ *
+ *    `state` must at least point to a readable memory block of size greater
+ *    than or equal to that of `bw_osc_filt_state`.
  *  }}} */
 
 #ifdef __cplusplus
@@ -131,32 +182,110 @@ extern "C" {
 #endif
 
 struct bw_osc_filt_state {
-	float	x_z1;
-	float	y_z1;
+#ifdef BW_DEBUG_DEEP
+	uint32_t	hash;
+#endif
+
+	// States
+	float	z1;
 };
 
-static inline void bw_osc_filt_reset_state(bw_osc_filt_state *BW_RESTRICT state) {
-	state->x_z1 = 0.f;
-	state->y_z1 = 0.f;
-}
+static inline float bw_osc_filt_reset_state(
+		bw_osc_filt_state * BW_RESTRICT state,
+		float                           x_0) {
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(bw_is_finite(x_0));
+
+	state->z1 = 0.f;
+	const float y = x_0;
+
+#ifdef BW_DEBUG_DEEP
+	state->hash = bw_hash_sdbm("bw_osc_filt_state");
+#endif
+	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
+	BW_ASSERT(bw_is_finite(y));
 
-static inline float bw_osc_filt_process1(bw_osc_filt_state *BW_RESTRICT state, float x) {
-	const float y = 1.371308261611209f * x + 0.08785458027104826f * state->x_z1 - 4.591628418822578e-1f * state->y_z1;
-	state->x_z1 = x;
-	state->y_z1 = y;
 	return y;
 }
 
-static inline void bw_osc_filt_process(bw_osc_filt_state *BW_RESTRICT state, const float *x, float *y, size_t n_samples) {
-	for (size_t i = 0; i < n_samples; i++)
-		y[i] = bw_osc_filt_process1(state, x[i]);
+static inline void bw_osc_filt_reset_state_multi(
+		bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float *                                       x_0,
+		float *                                             y_0,
+		size_t                                              n_channels) {
+	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_osc_filt_reset_state(state[i], x_0[i]);
+	else
+		for (size_t i = 0; i < n_channels; i++)
+			bw_osc_filt_reset_state(state[i], x_0[i]);
+
+	BW_ASSERT_DEEP(y_0 != NULL ? bw_has_only_finite(y_0, n_channels) : 1);
 }
 
-static inline void bw_osc_filt_process_multi(bw_osc_filt_state *BW_RESTRICT const *BW_RESTRICT state, const float * const *x, float * const *y, size_t n_channels, size_t n_samples) {
+static inline float bw_osc_filt_process1(
+		bw_osc_filt_state * BW_RESTRICT state,
+		float                           x) {
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
+	BW_ASSERT(bw_is_finite(x));
+
+	const float y = 1.371308261611209f * x + state->z1;
+	state->z1 = 0.08785458027104826f * x - 4.591628418822578e-1f * y;
+
+	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
+	BW_ASSERT(bw_is_finite(y));
+
+	return y;
+}
+
+static inline void bw_osc_filt_process(
+		bw_osc_filt_state * BW_RESTRICT state,
+		const float *                   x,
+		float *                         y,
+		size_t                          n_samples) {
+	BW_ASSERT(state != NULL);
+	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
+	BW_ASSERT(x != NULL);
+	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y != NULL);
+
+	for (size_t i = 0; i < n_samples; i++)
+		y[i] = bw_osc_filt_process1(state, x[i]);
+
+	BW_ASSERT_DEEP(bw_osc_filt_state_is_valid(state));
+	BW_ASSERT_DEEP(bw_has_only_finite(y, n_samples));
+}
+
+static inline void bw_osc_filt_process_multi(
+		bw_osc_filt_state * BW_RESTRICT const * BW_RESTRICT state,
+		const float * const *                               x,
+		float * const *                                     y,
+		size_t                                              n_channels,
+		size_t                                              n_samples) {
+	BW_ASSERT(state != NULL);
+	BW_ASSERT(x != NULL);
+	BW_ASSERT(y != NULL);
+
 	for (size_t i = 0; i < n_channels; i++)
 		bw_osc_filt_process(state[i], x[i], y[i], n_samples);
 }
 
+static inline char bw_osc_filt_state_is_valid(
+	const bw_osc_filt_state * BW_RESTRICT state) {
+	BW_ASSERT(state != NULL);
+
+#ifdef BW_DEBUG_DEEP
+	if (state->hash != bw_hash_sdbm("bw_osc_filt_state"))
+		return 0;
+#endif
+
+	return bw_is_finite(state->z1);
+}
+
 #ifdef __cplusplus
 }
 
@@ -174,15 +303,31 @@ class OscFilt {
 public:
 	OscFilt();
 	
-	void reset();
+	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);
 /*! <<<...
  *  }
  *  ```
@@ -194,8 +339,8 @@ public:
  * change at any time in future versions. Please, do not use it directly. */
 
 private:
-	bw_osc_filt_state	 states[N_CHANNELS];
-	bw_osc_filt_state	*BW_RESTRICT statesP[N_CHANNELS];
+	bw_osc_filt_state		states[N_CHANNELS];
+	bw_osc_filt_state * BW_RESTRICT	statesP[N_CHANNELS];
 };
 
 template<size_t N_CHANNELS>
@@ -205,24 +350,51 @@ inline OscFilt<N_CHANNELS>::OscFilt() {
 }
 
 template<size_t N_CHANNELS>
-inline void OscFilt<N_CHANNELS>::reset() {
-	for (size_t i = 0; i < N_CHANNELS; i++)
-		bw_osc_filt_reset_state(states + i);
+inline void OscFilt<N_CHANNELS>::reset(
+		float               x0,
+		float * BW_RESTRICT y0) {
+	if (y0 != nullptr)
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			y0[i] = bw_osc_filt_reset_state(states + i, x0);
+	else
+		for (size_t i = 0; i < N_CHANNELS; i++)
+			bw_osc_filt_reset_state(states + i, x0);
+}
+
+template<size_t N_CHANNELS>
+inline void OscFilt<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 OscFilt<N_CHANNELS>::reset(
+		const float * x0,
+		float *       y0) {
+	bw_osc_filt_reset_state_multi(statesP, x0, y0, N_CHANNELS);
+}
+
+template<size_t N_CHANNELS>
+inline void OscFilt<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 OscFilt<N_CHANNELS>::process(
-		const float * const *x,
-		float * const *y,
-		size_t nSamples) {
+		const float * const * x,
+		float * const *       y,
+		size_t                nSamples) {
 	bw_osc_filt_process_multi(statesP, x, y, N_CHANNELS, nSamples);
 }
 
 template<size_t N_CHANNELS>
 inline void OscFilt<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);
 }