audioconvert: add optional hilbert transform to rear channels

Add an option to do a hilbert transform on the generated rear channels
to do a 90 degree pahse shift on them. This can improve spacialization
of the rear channels.

See #861

spa/plugins/audioconvert/channelmix-ops-c.c

@@ -302,10 +302,10 @@ channelmix_f32_2_5p1_c(struct channelmix *mix, void * SPA_RESTRICT dst[],
 		lr4_process(&mix->lr4[2], d[2], d[3], v2, n_samples);
 		lr4_process(&mix->lr4[3], d[3], d[3], v3, n_samples);
 
-		delay_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
-				d[4], d[5], v4, n_samples);
+				mix->taps, mix->n_taps, d[4], d[5], v4, n_samples);
-		delay_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
-				d[5], d[5], v5, n_samples);
+				mix->taps, mix->n_taps, d[5], d[5], -v5, n_samples);
 	}
 	else {
 		for (n = 0; n < n_samples; n++) {
@@ -320,10 +320,10 @@ channelmix_f32_2_5p1_c(struct channelmix *mix, void * SPA_RESTRICT dst[],
 		lr4_process(&mix->lr4[2], d[2], d[3], v2, n_samples);
 		lr4_process(&mix->lr4[3], d[3], d[3], v3, n_samples);
 
-		delay_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
-				d[4], d[5], v4, n_samples);
+				mix->taps, mix->n_taps, d[4], d[5], v4, n_samples);
-		delay_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
-				d[5], d[5], v5, n_samples);
+				mix->taps, mix->n_taps, d[5], d[5], -v5, n_samples);
 	}
 }
 
@@ -362,10 +362,10 @@ channelmix_f32_2_7p1_c(struct channelmix *mix, void * SPA_RESTRICT dst[],
 		lr4_process(&mix->lr4[2], d[2], d[3], v2, n_samples);
 		lr4_process(&mix->lr4[3], d[3], d[3], v3, n_samples);
 
-		delay_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
-				d[6], d[7], v6, n_samples);
+				mix->taps, mix->n_taps, d[6], d[7], v6, n_samples);
-		delay_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
-				d[7], d[7], v7, n_samples);
+				mix->taps, mix->n_taps, d[7], d[7], -v7, n_samples);
 	}
 	else {
 		for (n = 0; n < n_samples; n++) {
@@ -382,10 +382,10 @@ channelmix_f32_2_7p1_c(struct channelmix *mix, void * SPA_RESTRICT dst[],
 		lr4_process(&mix->lr4[2], d[2], d[3], v2, n_samples);
 		lr4_process(&mix->lr4[3], d[3], d[3], v3, n_samples);
 
-		delay_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[0], &mix->pos[0], BUFFER_SIZE, mix->delay,
-				d[6], d[7], v6, n_samples);
+				mix->taps, mix->n_taps, d[6], d[7], v6, n_samples);
-		delay_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
+		delay_convolve_run(mix->buffer[1], &mix->pos[1], BUFFER_SIZE, mix->delay,
-				d[7], d[7], v7, n_samples);
+				mix->taps, mix->n_taps, d[7], d[7], -v7, n_samples);
 	}
 }
 

spa/plugins/audioconvert/channelmix-ops.c

@@ -35,6 +35,7 @@
 #define VOLUME_NORM 1.0f
 
 #include "channelmix-ops.h"
+#include "hilbert.h"
 
 #undef SPA_LOG_TOPIC_DEFAULT
 #define SPA_LOG_TOPIC_DEFAULT log_topic
@@ -469,6 +470,7 @@ done:
 			for (j = 0; j < jc; j++)
 		                mix->matrix_orig[i][j] /= maxsum;
 	}
+
 	return 0;
 }
 
@@ -550,7 +552,16 @@ int channelmix_init(struct channelmix *mix)
 	mix->cpu_flags = info->cpu_flags;
 	mix->delay = mix->rear_delay * mix->freq / 1000.0f;
 
-	spa_log_debug(mix->log, "selected %s delay:%d", info->name, mix->delay);
+	spa_log_debug(mix->log, "selected %s delay:%d options:%08x", info->name, mix->delay,
+			mix->options);
 
+	if (mix->hilbert_taps > 0) {
+		mix->n_taps = SPA_CLAMP(mix->hilbert_taps, 15, 255) | 1;
+		blackman_window(mix->taps, mix->n_taps);
+		hilbert_generate(mix->taps, mix->n_taps);
+	} else {
+		mix->n_taps = 1;
+		mix->taps[0] = 1.0f;
+	}
 	return make_matrix(mix);
 }

spa/plugins/audioconvert/channelmix-ops.h

@@ -48,6 +48,9 @@ extern struct spa_log_topic *log_topic;
 
 #define BUFFER_SIZE 4096
 
+#define BUFFER_SIZE 4096
+#define MAX_TAPS 255
+
 struct channelmix {
 	uint32_t src_chan;
 	uint32_t dst_chan;
@@ -73,11 +76,14 @@ struct channelmix {
 	float lfe_cutoff;				/* in Hz, 0 is disabled */
 	float rear_delay;				/* in ms, 0 is disabled */
 	float widen;					/* stereo widen. 0 is disabled */
+	uint32_t hilbert_taps;				/* to phase shift, 0 disabled */
 	struct lr4 lr4[SPA_AUDIO_MAX_CHANNELS];
 
 	float buffer[2][BUFFER_SIZE];
 	uint32_t pos[2];
 	uint32_t delay;
+	float taps[MAX_TAPS];
+	uint32_t n_taps;
 
 	void (*process) (struct channelmix *mix, void * SPA_RESTRICT dst[],
 			const void * SPA_RESTRICT src[], uint32_t n_samples);

spa/plugins/audioconvert/channelmix.c

@@ -527,6 +527,15 @@ static int impl_node_enum_params(void *object, int seq,
 					this->mix.widen, 0.0, 1.0),
 				SPA_PROP_INFO_params, SPA_POD_Bool(true));
 			break;
+		case 15:
+			param = spa_pod_builder_add_object(&b,
+				SPA_TYPE_OBJECT_PropInfo, id,
+				SPA_PROP_INFO_name, SPA_POD_String("channelmix.hilbert-taps"),
+				SPA_PROP_INFO_description, SPA_POD_String("Taps for phase shift of rear"),
+				SPA_PROP_INFO_type, SPA_POD_CHOICE_RANGE_Int(
+					this->mix.hilbert_taps, 0, MAX_TAPS),
+				SPA_PROP_INFO_params, SPA_POD_Bool(true));
+			break;
 		default:
 			return 0;
 		}
@@ -582,6 +591,8 @@ static int impl_node_enum_params(void *object, int seq,
 			spa_pod_builder_float(&b, this->mix.rear_delay);
 			spa_pod_builder_string(&b, "channelmix.stereo-widen");
 			spa_pod_builder_float(&b, this->mix.widen);
+			spa_pod_builder_string(&b, "channelmix.hilbert-taps");
+			spa_pod_builder_int(&b, this->mix.hilbert_taps);
 			spa_pod_builder_pop(&b, &f[1]);
 			param = spa_pod_builder_pop(&b, &f[0]);
 			break;
@@ -621,6 +632,8 @@ static int channelmix_set_param(struct impl *this, const char *k, const char *s)
 		spa_atof(s, &this->mix.rear_delay);
 	else if (spa_streq(k, "channelmix.stereo-widen"))
 		spa_atof(s, &this->mix.widen);
+	else if (spa_streq(k, "channelmix.hilbert-taps"))
+		spa_atou32(s, &this->mix.hilbert_taps, 0);
 	else
 		return 0;
 	return 1;

spa/plugins/audioconvert/hilbert.h

@@ -0,0 +1,69 @@
+/* Hilbert function
+ *
+ * Copyright © 2021 Wim Taymans
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+ * DEALINGS IN THE SOFTWARE.
+ */
+
+#ifndef HILBERT_H
+#define HILBERT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <errno.h>
+#include <stddef.h>
+#include <math.h>
+
+static inline void blackman_window(float *taps, int n_taps)
+{
+	int n;
+	for (n = 0; n < n_taps; n++) {
+		float w = 2 * M_PI * n / (n_taps-1);
+		taps[n] = 0.3635819 - 0.4891775 * cos(w)
+			+ 0.1365995 * cos(2 * w) - 0.0106411 * cos(3 * w);
+	}
+}
+
+static inline int hilbert_generate(float *taps, int n_taps)
+{
+	int i;
+
+	if ((n_taps & 1) == 0)
+		return -EINVAL;
+
+	for (i = 0; i < n_taps; i++) {
+		int k = -(n_taps / 2) + i;
+		if (k & 1) {
+			float pk = M_PI * k;
+			taps[i] *= (1.0f - cosf(pk)) / pk;
+		} else {
+			taps[i] = 0.0f;
+		}
+	}
+	return 0;
+}
+
+#ifdef __cplusplus
+} /* extern "C" */
+#endif
+
+#endif /* HILBERT_H */

src/daemon/client-rt.conf.in

@@ -87,4 +87,5 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }

src/daemon/client.conf.in

@@ -77,4 +77,5 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }

src/daemon/minimal.conf.in

@@ -208,6 +208,7 @@ context.objects = [
             #channelmix.lfe-cutoff  = 0
             #channelmix.rear-delay  = 12.0
             #channelmix.stereo-widen = 0.0
+            #channelmix.hilbert-taps = 0
             channelmix.disable     = true
             #node.param.Props      = {
             #    params = [
@@ -265,6 +266,7 @@ context.objects = [
             #channelmix.lfe-cutoff = 0
             #channelmix.rear-delay = 12.0
             #channelmix.stereo-widen = 0.0
+            #channelmix.hilbert-taps = 0
             channelmix.disable     = true
             #node.param.Props      = {
             #    params = [

src/daemon/pipewire-pulse.conf.in

@@ -87,6 +87,7 @@ stream.properties = {
     #channelmix.lfe-cutoff = 0
     #channelmix.rear-delay = 12.0
     #channelmix.stereo-widen = 0.0
+    #channelmix.hilbert-taps = 0
 }
 
 # client/stream specific properties