diff --git a/TODO b/TODO
index 7313c3a..9ca123c 100644
--- a/TODO
+++ b/TODO
@@ -70,6 +70,7 @@ code:
 * are we sure about inlining everything?
 * reset style is not enough when you have feedbacks... (see reverb)
 * IMPLEMENTATION/DECL/DEF prepocessor defs, maybe if DECL/DEF is defined then IMPLEMENTATION is needed to get implementation, etc.
+* actually assert no buffer overlap
 
 build system:
 * make makefiles handle paths with spaces etc
diff --git a/include/bw_balance.h b/include/bw_balance.h
index 6024362..b742157 100644
--- a/include/bw_balance.h
+++ b/include/bw_balance.h
@@ -382,6 +382,7 @@ static inline void bw_balance_process_multi(
 	BW_ASSERT(x_r != NULL);
 	BW_ASSERT(y_l != NULL);
 	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++) {
diff --git a/include/bw_env_follow.h b/include/bw_env_follow.h
index cf65e7e..d190933 100644
--- a/include/bw_env_follow.h
+++ b/include/bw_env_follow.h
@@ -516,7 +516,7 @@ static inline void bw_env_follow_process_multi(
 	if (y != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] != y[j]);
+				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
 #endif
 
 	bw_env_follow_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_env_gen.h b/include/bw_env_gen.h
index 68229e9..5923f9b 100644
--- a/include/bw_env_gen.h
+++ b/include/bw_env_gen.h
@@ -691,7 +691,7 @@ static inline void bw_env_gen_process_multi(
 	if (y != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] != y[j]);
+				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
 #endif
 
 	bw_env_gen_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_one_pole.h b/include/bw_one_pole.h
index fae1632..682d5ce 100644
--- a/include/bw_one_pole.h
+++ b/include/bw_one_pole.h
@@ -894,7 +894,7 @@ static inline void bw_one_pole_process_multi(
 	if (y != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] != y[j]);
+				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
 #endif
 
 	bw_one_pole_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_pan.h b/include/bw_pan.h
index 52098f7..4aaf4d8 100644
--- a/include/bw_pan.h
+++ b/include/bw_pan.h
@@ -374,6 +374,7 @@ static inline void bw_pan_process_multi(
 	BW_ASSERT(x != NULL);
 	BW_ASSERT(y_l != NULL);
 	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++) {
diff --git a/include/bw_ppm.h b/include/bw_ppm.h
index 0f42963..be3b7a9 100644
--- a/include/bw_ppm.h
+++ b/include/bw_ppm.h
@@ -506,7 +506,7 @@ static inline void bw_ppm_process_multi(
 	if (y != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] != y[j]);
+				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
 #endif
 
 	bw_ppm_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_reverb.h b/include/bw_reverb.h
index e60fa0e..1cada0b 100644
--- a/include/bw_reverb.h
+++ b/include/bw_reverb.h
@@ -837,6 +837,7 @@ static inline void bw_reverb_process1(
 	BW_ASSERT(bw_is_finite(x_r));
 	BW_ASSERT(y_l != NULL);
 	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != y_r);
 
 	const float i = 0.5f * (x_l + x_r);
 	const float pd = bw_delay_process1(&coeffs->predelay_coeffs, &state->predelay_state, i);
@@ -947,6 +948,7 @@ static inline void bw_reverb_process(
 	BW_ASSERT_DEEP(bw_has_only_finite(x_r, n_samples));
 	BW_ASSERT(y_l != NULL);
 	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != y_r);
 
 	bw_reverb_update_coeffs_ctrl(coeffs);
 	for (size_t i = 0; i < n_samples; i++) {
@@ -984,19 +986,16 @@ static inline void bw_reverb_process_multi(
 	BW_ASSERT(x_r != NULL);
 	BW_ASSERT(y_l != NULL);
 	BW_ASSERT(y_r != NULL);
+	BW_ASSERT(y_l != y_r);
 #ifndef BW_NO_DEBUG
-	if (y_l_0 != NULL)
-		for (size_t i = 0; i < n_channels; i++)
-			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_l_0[i] != y_l_0[j]);
-	if (y_r_0 != NULL)
-		for (size_t i = 0; i < n_channels; i++)
-			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_r_0[i] != y_r_0[j]);
-	if (y_l_0 != y_r_0)
-		for (size_t i = 0; i < n_channels; i++)
-			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_l_0[i] != y_r_0[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = i + 1; j < n_channels; j++) {
+			BW_ASSERT(y_l[i] != y_l[j]);
+			BW_ASSERT(y_r[i] != y_r[j]);
+		}
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(y_l[i] != y_r[j]);
 #endif
 
 	bw_reverb_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_slew_lim.h b/include/bw_slew_lim.h
index 218dc25..afe3a4a 100644
--- a/include/bw_slew_lim.h
+++ b/include/bw_slew_lim.h
@@ -674,7 +674,7 @@ static inline void bw_slew_lim_process_multi(
 	if (y != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y[i] != y[j]);
+				BW_ASSERT(y[i] == NULL || y[j] == NULL || y[i] != y[j]);
 #endif
 
 	bw_slew_lim_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_src.h b/include/bw_src.h
index 5a11c72..eb4e617 100644
--- a/include/bw_src.h
+++ b/include/bw_src.h
@@ -454,6 +454,7 @@ static inline void bw_src_process_multi(
 #endif
 	BW_ASSERT(x != NULL);
 	BW_ASSERT(y != NULL);
+	BW_ASSERT((void *)x != (void *)y);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
diff --git a/include/bw_src_int.h b/include/bw_src_int.h
index 4e46e49..c5f6645 100644
--- a/include/bw_src_int.h
+++ b/include/bw_src_int.h
@@ -430,6 +430,7 @@ static inline void bw_src_int_process_multi(
 #endif
 	BW_ASSERT(x != NULL);
 	BW_ASSERT(y != NULL);
+	BW_ASSERT((void *)x != (void *)y);
 #ifndef BW_NO_DEBUG
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
diff --git a/include/bw_svf.h b/include/bw_svf.h
index 67be868..3f3428e 100644
--- a/include/bw_svf.h
+++ b/include/bw_svf.h
@@ -678,6 +678,9 @@ static inline void bw_svf_process(
 	BW_ASSERT_DEEP(bw_svf_state_is_valid(coeffs, state));
 	BW_ASSERT(x != NULL);
 	BW_ASSERT_DEEP(bw_has_only_finite(x, n_samples));
+	BW_ASSERT(y_lp == NULL || y_bp == NULL || y_lp != y_bp);
+	BW_ASSERT(y_lp == NULL || y_hp == NULL || y_lp != y_hp);
+	BW_ASSERT(y_bp == NULL || y_hp == NULL || y_bp != y_hp);
 
 	if (y_lp != NULL) {
 		if (y_bp != NULL) {
@@ -767,31 +770,34 @@ static inline void bw_svf_process_multi(
 			BW_ASSERT(state[i] != state[j]);
 #endif
 	BW_ASSERT(x != NULL);
+	BW_ASSERT(y_lp == NULL || y_bp == NULL || y_lp != y_bp);
+	BW_ASSERT(y_lp == NULL || y_hp == NULL || y_lp != y_hp);
+	BW_ASSERT(y_bp == NULL || y_hp == NULL || y_bp != y_hp);
 #ifndef BW_NO_DEBUG
 	if (y_lp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] != y_lp[j]);
+				BW_ASSERT(y_lp[i] == NULL || y_lp[j] == NULL || y_lp[i] != y_lp[j]);
 	if (y_bp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_bp[i] != y_bp[j]);
+				BW_ASSERT(y_bp[i] == NULL || y_bp[j] == NULL || y_bp[i] != y_bp[j]);
 	if (y_hp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_hp[i] != y_hp[j]);
+				BW_ASSERT(y_hp[i] == NULL || y_hp[j] == NULL || y_hp[i] != y_hp[j]);
 	if (y_lp != NULL && y_bp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] != y_bp[j]);
+				BW_ASSERT(y_lp[i] == NULL || y_bp[j] == NULL || y_lp[i] != y_bp[j]);
 	if (y_lp != NULL && y_hp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_lp[i] != y_hp[j]);
+				BW_ASSERT(y_lp[i] == NULL || y_hp[j] == NULL || y_lp[i] != y_hp[j]);
 	if (y_bp != NULL && y_hp != NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y_bp[i] != y_hp[j]);
+				BW_ASSERT(y_bp[i] == NULL || y_hp[j] == NULL || y_bp[i] != y_hp[j]);
 #endif
 
 	if (y_lp != NULL) {