diff --git a/include/bw_ap1.h b/include/bw_ap1.h
index 26ebbca..137a3cb 100644
--- a/include/bw_ap1.h
+++ b/include/bw_ap1.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order allpass filter (90° shift at cutoff, approaching 180° shift
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_ap1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -518,6 +525,9 @@ static inline void bw_ap1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_ap1_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_ap2.h b/include/bw_ap2.h
index a8efd2c..ee1566f 100644
--- a/include/bw_ap2.h
+++ b/include/bw_ap2.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order allpass filter (180° shift at cutoff, approaching 360° shift
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_ap2_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -531,6 +538,9 @@ static inline void bw_ap2_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_ap2_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_balance.h b/include/bw_balance.h
index 6bfb8fe..28279b0 100644
--- a/include/bw_balance.h
+++ b/include/bw_balance.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole }}}
  *  description {{{
  *    Stereo balance.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_balance_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -398,6 +405,13 @@ static inline void bw_balance_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || x_l[i] != y_l[j]);
+			BW_ASSERT(i == j || x_l[i] != y_r[j]);
+			BW_ASSERT(i == j || x_r[i] != y_l[j]);
+			BW_ASSERT(i == j || x_r[i] != y_r[j]);
+		}
 #endif
 
 	bw_balance_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_bd_reduce.h b/include/bw_bd_reduce.h
index 99c9828..0a2fb35 100644
--- a/include/bw_bd_reduce.h
+++ b/include/bw_bd_reduce.h
@@ -28,14 +28,16 @@
  *    This is purely an audio effect, it doesn't actually produce an output
  *    signal with a different encoding. The algorithm is deliberately crude to
  *    obtain the characteristic noise due to lo-fi A/D quantization.
- *
- *    It 
  *  }}}
  *  changelog {{{
  *    <ul>
  *      <li>Version <strong>1.2.0</strong>:
  *        <ul>
  *          <li>Added gate parameter.</li>
+ *          <li>Added debugging check in
+ *              <code>bw_balance_bd_reduce_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>1.1.0</strong>:
@@ -409,6 +411,9 @@ static inline void bw_bd_reduce_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_bd_reduce_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_buf.h b/include/bw_buf.h
index 7b66467..6b18fbd 100644
--- a/include/bw_buf.h
+++ b/include/bw_buf.h
@@ -20,13 +20,21 @@
 
 /*!
  *  module_type {{{ utility }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Common operations on buffers.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_buf_{neg,add,scale,mix,mul}_multi()</code> to ensure
+ *              that buffers used for both input and output appear at the same
+ *              channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -362,6 +370,9 @@ static inline void bw_buf_neg_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(dest[i] != dest[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || src[i] != dest[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
@@ -381,6 +392,9 @@ static inline void bw_buf_add_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(dest[i] != dest[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || src[i] != dest[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
@@ -400,6 +414,9 @@ static inline void bw_buf_scale_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(dest[i] != dest[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || src[i] != dest[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
@@ -419,6 +436,11 @@ static inline void bw_buf_mix_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(dest[i] != dest[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || src1[i] != dest[j]);
+			BW_ASSERT(i == j || src2[i] != dest[j]);
+		}
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
@@ -438,6 +460,11 @@ static inline void bw_buf_mul_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(dest[i] != dest[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || src1[i] != dest[j]);
+			BW_ASSERT(i == j || src2[i] != dest[j]);
+		}
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
diff --git a/include/bw_cab.h b/include/bw_cab.h
index dd41aa9..e4ea388 100644
--- a/include/bw_cab.h
+++ b/include/bw_cab.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.0.0 }}}
+ *  version {{{ 1.0.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Cab simulator effect.
@@ -30,6 +30,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.0.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_cab_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.0.0</strong>:
  *        <ul>
  *          <li>First release.</li>
@@ -528,6 +535,9 @@ static inline void bw_cab_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_cab_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_chorus.h b/include/bw_chorus.h
index fcfa14d..ca7f1d8 100644
--- a/include/bw_chorus.h
+++ b/include/bw_chorus.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_buf bw_comb bw_common bw_delay bw_gain bw_math bw_one_pole bw_osc_sin
  *    bw_phase_gen
@@ -36,6 +36,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_chorus_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -662,6 +669,9 @@ static inline void bw_chorus_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_chorus_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_clip.h b/include/bw_clip.h
index deec8a9..053f80c 100644
--- a/include/bw_clip.h
+++ b/include/bw_clip.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Antialiased hard clipper with parametric bias and gain
@@ -45,6 +45,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_clip_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -600,6 +607,9 @@ static inline void bw_clip_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	if (coeffs->gain_compensation)
diff --git a/include/bw_comb.h b/include/bw_comb.h
index 9beed5b..855f982 100644
--- a/include/bw_comb.h
+++ b/include/bw_comb.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_buf bw_common bw_delay bw_gain bw_math bw_one_pole
  *  }}}
@@ -37,6 +37,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_comb_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -718,6 +725,9 @@ static inline void bw_comb_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_comb_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_comp.h b/include/bw_comp.h
index 695acb6..c64351c 100644
--- a/include/bw_comp.h
+++ b/include/bw_comp.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_common bw_env_follow bw_gain bw_math bw_one_pole
  *  }}}
@@ -29,6 +29,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_comp_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Relaxed <code>bw_comp_reset_state_multi</code>,
@@ -658,6 +665,13 @@ static inline void bw_comp_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
+	if (x_sc != BW_NULL)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x_sc[i] != y[j]);
 #endif
 
 	bw_comp_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_delay.h b/include/bw_delay.h
index 1713c09..d880219 100644
--- a/include/bw_delay.h
+++ b/include/bw_delay.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_buf bw_common bw_math }}}
  *  description {{{
  *    Interpolated delay line, not smoothed.
@@ -31,6 +31,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_delay_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -667,6 +674,9 @@ static inline void bw_delay_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_delay_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_dist.h b/include/bw_dist.h
index 7b263d1..8139c85 100644
--- a/include/bw_dist.h
+++ b/include/bw_dist.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_clip bw_common bw_gain bw_hp1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_dist_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -558,6 +565,9 @@ static inline void bw_dist_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_dist_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_drive.h b/include/bw_drive.h
index c6df218..c9c2a10 100644
--- a/include/bw_drive.h
+++ b/include/bw_drive.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_common bw_gain bw_hs1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_drive_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -561,6 +568,9 @@ static inline void bw_drive_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_drive_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_dry_wet.h b/include/bw_dry_wet.h
index 0d69093..e97292f 100644
--- a/include/bw_dry_wet.h
+++ b/include/bw_dry_wet.h
@@ -32,6 +32,9 @@
  *          <li>Added <code>bw_dry_wet_get_wet()</code> and
  *              <code>bw_dry_wet_get_wet_cur()</code>, and corresponding C++
  *              API.</li>
+ *          <li>Added debugging check in <code>bw_dry_wet_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
  *        </ul>
  *      </li>
  *      <li>Version <strong>1.1.0</strong>:
@@ -379,6 +382,11 @@ static inline void bw_dry_wet_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || x_dry[i] != y[j]);
+			BW_ASSERT(i == j || x_wet[i] != y[j]);
+		}
 #endif
 
 	bw_dry_wet_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_env_follow.h b/include/bw_env_follow.h
index 96bab6d..e497e44 100644
--- a/include/bw_env_follow.h
+++ b/include/bw_env_follow.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Envelope follower made of a full-wave rectifier followed by
@@ -28,6 +28,14 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_env_follow_process_multi()</code> to ensure that
+ *              buffers used for both input and output appear at the same
+ *              channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -521,10 +529,14 @@ static inline void bw_env_follow_process_multi(
 #endif
 	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != BW_NULL)
+	if (y != BW_NULL) {
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y[j]);
+	}
 #endif
 
 	bw_env_follow_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_fuzz.h b/include/bw_fuzz.h
index 7222ba2..1aaa7b1 100644
--- a/include/bw_fuzz.h
+++ b/include/bw_fuzz.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_common bw_gain bw_hp1 bw_lp1 bw_math bw_mm2 bw_one_pole bw_peak
  *    bw_satur bw_svf
@@ -32,6 +32,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_fuzz_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -547,6 +554,9 @@ static inline void bw_fuzz_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_fuzz_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_gain.h b/include/bw_gain.h
index 092169a..d3af93a 100644
--- a/include/bw_gain.h
+++ b/include/bw_gain.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_gain_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -405,6 +412,9 @@ static inline void bw_gain_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_gain_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_hp1.h b/include/bw_hp1.h
index 5d12252..325805f 100644
--- a/include/bw_hp1.h
+++ b/include/bw_hp1.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order highpass filter (6 dB/oct) with gain asymptotically
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_hp1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -514,6 +521,9 @@ static inline void bw_hp1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_hp1_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_hs1.h b/include/bw_hs1.h
index 75d40bd..1cc59d0 100644
--- a/include/bw_hs1.h
+++ b/include/bw_hs1.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_mm1 bw_one_pole }}}
  *  description {{{
  *    First-order high shelf filter (6 dB/oct) with unitary DC gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_hs1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -590,6 +597,9 @@ static inline void bw_hs1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_hs1_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_hs2.h b/include/bw_hs2.h
index 6a60062..153764a 100644
--- a/include/bw_hs2.h
+++ b/include/bw_hs2.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_mm2 bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order high shelf filter (12 dB/oct) with unitary DC gain.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_hs2_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -618,6 +625,9 @@ static inline void bw_hs2_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_hs2_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_lp1.h b/include/bw_lp1.h
index ce60d31..2a2a6d1 100644
--- a/include/bw_lp1.h
+++ b/include/bw_lp1.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    First-order lowpass filter (6 dB/oct) with unitary DC gain.
@@ -30,6 +30,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_lp1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -565,6 +572,9 @@ static inline void bw_lp1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	for (size_t i = 0; i < n_samples; i++) {
diff --git a/include/bw_ls1.h b/include/bw_ls1.h
index 96428a1..8513557 100644
--- a/include/bw_ls1.h
+++ b/include/bw_ls1.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_mm1 bw_one_pole }}}
  *  description {{{
  *    First-order low shelf filter (6 dB/oct) with gain asymptotically
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_ls1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -588,6 +595,9 @@ static inline void bw_ls1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_ls1_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_ls2.h b/include/bw_ls2.h
index 5dd6da3..66e27c5 100644
--- a/include/bw_ls2.h
+++ b/include/bw_ls2.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_mm2 bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order low shelf filter (12 dB/oct) with gain asymptotically
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_ls2_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -624,6 +631,9 @@ static inline void bw_ls2_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_ls2_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_mm1.h b/include/bw_mm1.h
index 08f4304..fc19c70 100644
--- a/include/bw_mm1.h
+++ b/include/bw_mm1.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_lp1 bw_math bw_one_pole }}}
  *  description {{{
  *    First-order multimode filter.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_mm1_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Fixed computation of initial state in
@@ -557,6 +564,9 @@ static inline void bw_mm1_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_mm1_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_mm2.h b/include/bw_mm2.h
index b3116a4..55a28a2 100644
--- a/include/bw_mm2.h
+++ b/include/bw_mm2.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order multimode filter.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_mm2_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Fixed computation of initial state in
@@ -618,6 +625,9 @@ static inline void bw_mm2_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_mm2_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_noise_gate.h b/include/bw_noise_gate.h
index 66e7b01..f0168cc 100644
--- a/include/bw_noise_gate.h
+++ b/include/bw_noise_gate.h
@@ -20,13 +20,21 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_env_follow bw_math bw_one_pole }}}
  *  description {{{
  *    Noise gate with independent sidechain input.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_noise_gate_process_multi()</code> to ensure that
+ *              buffers used for both input and output appear at the same
+ *              channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Relaxed <code>bw_noise_gate_reset_state_multi</code>,
@@ -598,7 +606,8 @@ static inline void bw_noise_gate_process(
 static inline void bw_noise_gate_process_multi(
 		bw_noise_gate_coeffs * BW_RESTRICT                    coeffs,
 		bw_noise_gate_state * BW_RESTRICT const * BW_RESTRICT state,
-		const float * const * x, const float * const *        x_sc,
+		const float * const *                                 x,
+		const float * const *                                 x_sc,
 		float * const *                                       y,
 		size_t                                                n_channels,
 		size_t                                                n_samples) {
@@ -617,6 +626,13 @@ static inline void bw_noise_gate_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
+	if (x_sc != BW_NULL)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x_sc[i] != y[j]);
 #endif
 
 	bw_noise_gate_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_notch.h b/include/bw_notch.h
index 52d74e3..3807d66 100644
--- a/include/bw_notch.h
+++ b/include/bw_notch.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order notch filter with unitary gain at DC and asymptotically as
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_notch_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -529,6 +536,9 @@ static inline void bw_notch_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_notch_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_one_pole.h b/include/bw_one_pole.h
index 4c638a0..6d47693 100644
--- a/include/bw_one_pole.h
+++ b/include/bw_one_pole.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    One-pole (6 dB/oct) lowpass filter with unitary DC gain, separate attack
@@ -30,6 +30,14 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_one_pole_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -901,10 +909,14 @@ static inline void bw_one_pole_process_multi(
 #endif
 	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != BW_NULL)
+	if (y != BW_NULL) {
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y[j]);
+	}
 #endif
 
 	bw_one_pole_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_osc_filt.h b/include/bw_osc_filt.h
index 852ac2a..805949c 100644
--- a/include/bw_osc_filt.h
+++ b/include/bw_osc_filt.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Post-filter to decolorate oscillator waveshapers when antialiasing is on.
@@ -33,6 +33,14 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_osc_filt_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -290,6 +298,9 @@ static inline void bw_osc_filt_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
diff --git a/include/bw_osc_pulse.h b/include/bw_osc_pulse.h
index fde1832..6f2b7d6 100644
--- a/include/bw_osc_pulse.h
+++ b/include/bw_osc_pulse.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Pulse oscillator waveshaper with variable pulse width (actually, duty
@@ -37,6 +37,15 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging checks in
+ *              <code>bw_osc_pulse_process_multi()</code> to ensure that
+ *              <code>x_inc</code> is not <code>BW_NULL</code> when antialiasing
+ *              is on and that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -467,11 +476,19 @@ static inline void bw_osc_pulse_process_multi(
 	BW_ASSERT_DEEP(bw_osc_pulse_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_pulse_coeffs_state_reset_coeffs);
 	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
+	if (coeffs->antialiasing)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x_inc[i] != y[j]);
 #endif
 
 	if (coeffs->antialiasing)
diff --git a/include/bw_osc_saw.h b/include/bw_osc_saw.h
index 5ac7fde..7f43f0a 100644
--- a/include/bw_osc_saw.h
+++ b/include/bw_osc_saw.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sawtooth oscillator waveshaper with PolyBLEP antialiasing.
@@ -36,6 +36,15 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging checks in
+ *              <code>bw_osc_saw_process_multi()</code> to ensure that
+ *              <code>x_inc</code> is not <code>BW_NULL</code> when antialiasing
+ *              is on and that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -434,11 +443,19 @@ static inline void bw_osc_saw_process_multi(
 	BW_ASSERT_DEEP(bw_osc_saw_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_saw_coeffs_state_reset_coeffs);
 	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
+	if (coeffs->antialiasing)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x_inc[i] != y[j]);
 #endif
 
 	if (x_inc != BW_NULL)
diff --git a/include/bw_osc_sin.h b/include/bw_osc_sin.h
index 3463ef3..b601d48 100644
--- a/include/bw_osc_sin.h
+++ b/include/bw_osc_sin.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sinusoidal oscillator waveshaper.
@@ -30,6 +30,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_osc_sin_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -176,6 +183,9 @@ static inline void bw_osc_sin_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
diff --git a/include/bw_osc_tri.h b/include/bw_osc_tri.h
index f46a70f..bdfba0d 100644
--- a/include/bw_osc_tri.h
+++ b/include/bw_osc_tri.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Triangle oscillator waveshaper with variable slope (increasing time over
@@ -37,6 +37,15 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging checks in
+ *              <code>bw_osc_tri_process_multi()</code> to ensure that
+ *              <code>x_inc</code> is not <code>BW_NULL</code> when antialiasing
+ *              is on and that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -474,11 +483,19 @@ static inline void bw_osc_tri_process_multi(
 	BW_ASSERT_DEEP(bw_osc_tri_coeffs_is_valid(coeffs));
 	BW_ASSERT_DEEP(coeffs->state >= bw_osc_tri_coeffs_state_reset_coeffs);
 	BW_ASSERT(x != BW_NULL);
+	BW_ASSERT(coeffs->antialiasing ? x_inc != BW_NULL : 1);
 	BW_ASSERT(y != BW_NULL);
 #ifndef BW_NO_DEBUG
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
+	if (coeffs->antialiasing)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x_inc[i] != y[j]);
 #endif
 
 	if (coeffs->antialiasing)
diff --git a/include/bw_pan.h b/include/bw_pan.h
index 8bc369a..cf7b47d 100644
--- a/include/bw_pan.h
+++ b/include/bw_pan.h
@@ -20,13 +20,20 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_one_pole }}}
  *  description {{{
  *    Stereo panner with -3 dB center pan law.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_pan_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -390,6 +397,11 @@ static inline void bw_pan_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || x[i] != y_l[j]);
+			BW_ASSERT(i == j || x[i] != y_r[j]);
+		}
 #endif
 
 	bw_pan_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_peak.h b/include/bw_peak.h
index bbfe8ff..e5b6d39 100644
--- a/include/bw_peak.h
+++ b/include/bw_peak.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_gain bw_math bw_mm2 bw_one_pole bw_svf }}}
  *  description {{{
  *    Second-order peak filter with unitary gain at DC and asymptotically
@@ -35,6 +35,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_peak_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -678,6 +685,9 @@ static inline void bw_peak_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_peak_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_phase_gen.h b/include/bw_phase_gen.h
index df72896..1693d3e 100644
--- a/include/bw_phase_gen.h
+++ b/include/bw_phase_gen.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Phase generator with portamento and exponential frequency modulation.
@@ -29,6 +29,17 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_phase_gen_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *          <li>Fixed bug in <code>bw_phase_gen_process_multi()</code> by which
+ *              debugging code could report false negatives when
+ *              <code>BW_NULL</code> buffers are used.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Fixed rounding bug when frequency is tiny and negative.</li>
@@ -682,15 +693,25 @@ static inline void bw_phase_gen_process_multi(
 	if (y != BW_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] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
 	if (y_inc != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
-				BW_ASSERT(y_inc[i] != y_inc[j]);
+				BW_ASSERT(y_inc[i] == BW_NULL || y_inc[j] == BW_NULL || y_inc[i] != y_inc[j]);
 	if (y != BW_NULL && y_inc != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
-				BW_ASSERT(y[i] != y_inc[j]);
+				BW_ASSERT(y[i] == BW_NULL || y_inc[j] == BW_NULL || y[i] != y_inc[j]);
+	if (x_mod != BW_NULL) {
+		if (y != BW_NULL)
+			for (size_t i = 0; i < n_channels; i++)
+				for (size_t j = 0; j < n_channels; j++)
+					BW_ASSERT(i == j || x_mod[i] == BW_NULL || y[i] == BW_NULL || x_mod[i] != y[j]);
+		if (y_inc != BW_NULL)
+			for (size_t i = 0; i < n_channels; i++)
+				for (size_t j = 0; j < n_channels; j++)
+					BW_ASSERT(i == j || x_mod[i] == BW_NULL || y_inc[i] == BW_NULL || x_mod[i] != y_inc[j]);
+	}
 #endif
 
 	bw_phase_gen_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_phaser.h b/include/bw_phaser.h
index 7597306..c73d0e4 100644
--- a/include/bw_phaser.h
+++ b/include/bw_phaser.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_ap1 bw_common bw_lp1 bw_math bw_one_pole bw_osc_sin bw_phase_gen
  *  }}}
@@ -30,6 +30,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_phaser_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -548,6 +555,9 @@ static inline void bw_phaser_process_multi(
 	for (size_t i = 0; i < n_channels; i++)
 		for (size_t j = i + 1; j < n_channels; j++)
 			BW_ASSERT(state[i] != state[j]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 	BW_ASSERT(x != BW_NULL);
 	BW_ASSERT(y != BW_NULL);
diff --git a/include/bw_pink_filt.h b/include/bw_pink_filt.h
index b5f7f2c..94f2b67 100644
--- a/include/bw_pink_filt.h
+++ b/include/bw_pink_filt.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common }}}
  *  description {{{
  *    Pinking filter.
@@ -40,6 +40,14 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_pink_filt_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -576,6 +584,9 @@ static inline void bw_pink_filt_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
diff --git a/include/bw_ppm.h b/include/bw_ppm.h
index 40542ee..6dfe5aa 100644
--- a/include/bw_ppm.h
+++ b/include/bw_ppm.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_env_follow bw_math bw_one_pole }}}
  *  description {{{
  *    Digital peak programme meter with adjustable integration time constant.
@@ -30,6 +30,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_ppm_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -509,10 +516,14 @@ static inline void bw_ppm_process_multi(
 #endif
 	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != BW_NULL)
+	if (y != BW_NULL) {
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y[j]);
+	}
 #endif
 
 	bw_ppm_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_reverb.h b/include/bw_reverb.h
index 4d7d6ea..177add1 100644
--- a/include/bw_reverb.h
+++ b/include/bw_reverb.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_buf bw_common bw_delay bw_dry_wet bw_gain bw_lp1 bw_math bw_one_pole
  *    bw_osc_sin bw_phase_gen
@@ -35,6 +35,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_reverb_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Fixed smoothing of decay parameter in
@@ -1004,6 +1011,13 @@ static inline void bw_reverb_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || x_l[i] != y_l[j]);
+			BW_ASSERT(i == j || x_l[i] != y_r[j]);
+			BW_ASSERT(i == j || x_r[i] != y_l[j]);
+			BW_ASSERT(i == j || x_r[i] != y_r[j]);
+		}
 #endif
 
 	bw_reverb_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_ring_mod.h b/include/bw_ring_mod.h
index d2b5cc0..b6c1be8 100644
--- a/include/bw_ring_mod.h
+++ b/include/bw_ring_mod.h
@@ -20,13 +20,21 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Ring modulator with variable modulation amount.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_ring_mod_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -362,6 +370,11 @@ static inline void bw_ring_mod_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++) {
+			BW_ASSERT(i == j || x_mod[i] != y[j]);
+			BW_ASSERT(i == j || x_car[i] != y[j]);
+		}
 #endif
 
 	for (size_t i = 0; i < n_samples; i++) {
diff --git a/include/bw_satur.h b/include/bw_satur.h
index d94bef3..d069216 100644
--- a/include/bw_satur.h
+++ b/include/bw_satur.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    Antialiased tanh-based saturation with parametric bias and gain
@@ -45,6 +45,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_satur_process_multi()</code>
+ *              to ensure that buffers used for both input and output appear at
+ *              the same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Fixed gain compensation in <code>bw_satur_process_multi().</li>
@@ -621,6 +628,9 @@ static inline void bw_satur_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_satur_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_slew_lim.h b/include/bw_slew_lim.h
index c9eb920..6bae932 100644
--- a/include/bw_slew_lim.h
+++ b/include/bw_slew_lim.h
@@ -20,13 +20,21 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Slew-rate limiter with separate maximum increasing and decreasing rates.
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_slew_lim_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -677,10 +685,14 @@ static inline void bw_slew_lim_process_multi(
 #endif
 	BW_ASSERT(x != BW_NULL);
 #ifndef BW_NO_DEBUG
-	if (y != BW_NULL)
+	if (y != BW_NULL) {
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = i + 1; j < n_channels; j++)
 				BW_ASSERT(y[i] == BW_NULL || y[j] == BW_NULL || y[i] != y[j]);
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y[j]);
+	}
 #endif
 
 	bw_slew_lim_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_sr_reduce.h b/include/bw_sr_reduce.h
index 03535d6..0337d94 100644
--- a/include/bw_sr_reduce.h
+++ b/include/bw_sr_reduce.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math }}}
  *  description {{{
  *    Sample rate reducer.
@@ -31,6 +31,14 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in
+ *              <code>bw_sr_reduce_process_multi()</code> to ensure that buffers
+ *              used for both input and output appear at the same channel
+ *              indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -494,6 +502,9 @@ static inline void bw_sr_reduce_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	for (size_t i = 0; i < n_channels; i++)
diff --git a/include/bw_svf.h b/include/bw_svf.h
index 6fa0bda..28a7d80 100644
--- a/include/bw_svf.h
+++ b/include/bw_svf.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole }}}
  *  description {{{
  *    State variable filter (2nd order, 12 dB/oct) model with separated lowpass,
@@ -28,6 +28,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_svf_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -773,18 +780,30 @@ static inline void bw_svf_process_multi(
 	BW_ASSERT(y_lp == BW_NULL || y_hp == BW_NULL || y_lp != y_hp);
 	BW_ASSERT(y_bp == BW_NULL || y_hp == BW_NULL || y_bp != y_hp);
 #ifndef BW_NO_DEBUG
-	if (y_lp != BW_NULL)
+	if (y_lp != BW_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] == BW_NULL || y_lp[j] == BW_NULL || y_lp[i] != y_lp[j]);
-	if (y_bp != BW_NULL)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y_lp[j]);
+	}
+	if (y_bp != BW_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] == BW_NULL || y_bp[j] == BW_NULL || y_bp[i] != y_bp[j]);
-	if (y_hp != BW_NULL)
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y_bp[j]);
+	}
+	if (y_hp != BW_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] == BW_NULL || y_hp[j] == BW_NULL || y_hp[i] != y_hp[j]);
+		for (size_t i = 0; i < n_channels; i++)
+			for (size_t j = 0; j < n_channels; j++)
+				BW_ASSERT(i == j || x[i] != y_hp[j]);
+	}
 	if (y_lp != BW_NULL && y_bp != BW_NULL)
 		for (size_t i = 0; i < n_channels; i++)
 			for (size_t j = 0; j < n_channels; j++)
diff --git a/include/bw_trem.h b/include/bw_trem.h
index bba2bae..56181b7 100644
--- a/include/bw_trem.h
+++ b/include/bw_trem.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{
  *    bw_common bw_math bw_one_pole bw_osc_sin bw_phase_gen bw_ring_mod
  *  }}}
@@ -29,6 +29,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_trem_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -511,6 +518,9 @@ static inline void bw_trem_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_trem_update_coeffs_ctrl(coeffs);
diff --git a/include/bw_wah.h b/include/bw_wah.h
index d9d1d98..1ee3db7 100644
--- a/include/bw_wah.h
+++ b/include/bw_wah.h
@@ -20,7 +20,7 @@
 
 /*!
  *  module_type {{{ dsp }}}
- *  version {{{ 1.1.0 }}}
+ *  version {{{ 1.1.1 }}}
  *  requires {{{ bw_common bw_math bw_one_pole bw_svf }}}
  *  description {{{
  *    Wah effect.
@@ -29,6 +29,13 @@
  *  }}}
  *  changelog {{{
  *    <ul>
+ *      <li>Version <strong>1.1.1</strong>:
+ *        <ul>
+ *          <li>Added debugging check in <code>bw_wah_process_multi()</code> to
+ *              ensure that buffers used for both input and output appear at the
+ *              same channel indices.</li>
+ *        </ul>
+ *      </li>
  *      <li>Version <strong>1.1.0</strong>:
  *        <ul>
  *          <li>Now using <code>BW_NULL</code> and
@@ -501,6 +508,9 @@ static inline void bw_wah_process_multi(
 	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]);
+	for (size_t i = 0; i < n_channels; i++)
+		for (size_t j = 0; j < n_channels; j++)
+			BW_ASSERT(i == j || x[i] != y[j]);
 #endif
 
 	bw_wah_update_coeffs_ctrl(coeffs);