test of ssb

modulation/stereo_encoder.c

@@ -1,23 +1,63 @@
 #include "stereo_encoder.h"
 
+#ifdef STEREO_SSB
+static void init_delay_line(struct delay_line_t *delay_line, uint32_t sample_rate) {
+	delay_line->buffer = malloc(sample_rate * sizeof(float));
+	memset(delay_line->buffer, 0, sample_rate * sizeof(float));
+}
+
+static void set_delay_line(struct delay_line_t *delay_line, uint32_t new_delay) {
+	delay_line->delay = new_delay;
+}
+
+static inline float delay_line(struct delay_line_t *delay_line, float in) {
+	delay_line->buffer[delay_line->idx++] = in;
+	if (delay_line->idx >= delay_line->delay) delay_line->idx = 0;
+	return delay_line->buffer[delay_line->idx];
+}
+
+static void exit_delay_line(struct delay_line_t *delay_line) {
+	free(delay_line->buffer);
+}
+#endif
+
 // Multiplier is the multiplier to get to 19 khz
 void init_stereo_encoder(StereoEncoder* st, uint8_t multiplier, Oscillator* osc, float audio_volume, float pilot_volume) {
     st->multiplier = multiplier;
     st->osc = osc;
     st->pilot_volume = pilot_volume;
     st->audio_volume = audio_volume;
+#ifdef STEREO_SSB
+    init_delay_line(&st->delay, 15); // 7*2+1
+#endif
 }
 
+#ifdef STEREO_SSB
+float stereo_encode(StereoEncoder* st, uint8_t enabled, float left, float right, firhilbf hilbert) {
+#else
 float stereo_encode(StereoEncoder* st, uint8_t enabled, float left, float right) {
+#endif
     float mid = (left+right) * 0.5f;
     if(!enabled) return mid * st->audio_volume;
+    mid = delay_line(&st->delay, mid);
 
     float half_audio = st->audio_volume * 0.5f;
 
     float side = (left-right) * 0.5f;
+
+#ifdef STEREO_SSB
+    float complex stereo_hilbert;
+    firhilbf_r2c_execute(hilbert, side, &stereo_hilbert);
+    float signalx2cos = get_oscillator_cos_multiplier_ni(st->osc, st->multiplier * 2.0f);
+#endif
     
     float signalx1 = get_oscillator_sin_multiplier_ni(st->osc, st->multiplier);
     float signalx2 = get_oscillator_sin_multiplier_ni(st->osc, st->multiplier * 2.0f);
 
+#ifdef STEREO_SSB
+    float stereo = (crealf(stereo_hilbert) * signalx2cos) - (cimagf(stereo_hilbert) * signalx2);
+    return (mid*half_audio) + (signalx1*st->pilot_volume) + (stereo * half_audio);
+#else
     return (mid*half_audio) + (signalx1*st->pilot_volume) + ((side*signalx2) * half_audio);
+#endif
 }

modulation/stereo_encoder.h

@@ -1,7 +1,19 @@
 #pragma once
 
+#define STEREO_SSB
+
 #include <stdint.h>
 #include "../dsp/oscillator.h"
+#ifdef STEREO_SSB
+#include <liquid/liquid.h>
+#include <complex.h>
+
+typedef struct delay_line_t {
+	float *buffer;
+	uint32_t delay;
+	uint32_t idx;
+} delay_line_t;
+#endif
 
 typedef struct
 {
@@ -9,8 +21,15 @@ typedef struct
     Oscillator* osc;
     float audio_volume;
     float pilot_volume;
+#ifdef STEREO_SSB
+    struct delay_line_t delay;
+#endif
 } StereoEncoder;
 
 void init_stereo_encoder(StereoEncoder *st, uint8_t multiplier, Oscillator *osc, float audio_volume, float pilot_volume);
 
+#ifdef STEREO_SSB
+float stereo_encode(StereoEncoder* st, uint8_t enabled, float left, float right, firhilbf hilbert);
+#else
 float stereo_encode(StereoEncoder* st, uint8_t enabled, float left, float right);
+#endif

src/fm95.c

@@ -83,6 +83,9 @@ typedef struct
 	float* rds_in;
 	Oscillator osc;
 	iirfilt_rrrf lpf_l, lpf_r;
+	#ifdef STEREO_SSB
+	firhilbf stereo_hilbert;
+	#endif
 	ResistorCapacitor preemp_l, preemp_r;
 	BS412Compressor bs412;
 	StereoEncoder stencode;
@@ -140,6 +143,10 @@ void cleanup_runtime(FM95_Runtime* runtime, const FM95_Config config) {
 		iirfilt_rrrf_destroy(runtime->lpf_l);
 		iirfilt_rrrf_destroy(runtime->lpf_r);
 	}
+	#ifdef STEREO_SSB
+	firhilbf_destroy(runtime->stereo_hilbert);
+	free(runtime->stencode.delay.buffer);
+	#endif
 }
 
 void cleanup_audio_runtime(FM95_Runtime *rt, const FM95_Options options) {
@@ -481,6 +488,10 @@ void init_runtime(FM95_Runtime* runtime, const FM95_Config config) {
 		runtime->lpf_r = iirfilt_rrrf_create_prototype(LIQUID_IIRDES_CHEBY2, LIQUID_IIRDES_LOWPASS, LIQUID_IIRDES_SOS, config.lpf_order, (config.lpf_cutoff/config.sample_rate), 0.0f, 1.0f, 60.0f);
 	}
 
+	#ifdef STEREO_SSB
+	runtime->stereo_hilbert = firhilbf_create(7, 60);
+	#endif
+
 	if(config.preemphasis != 0) {
 		init_preemphasis(&runtime->preemp_l, (float)config.preemphasis * 1.0e-6f, config.sample_rate, config.preemp_unity_freq);
 		init_preemphasis(&runtime->preemp_r, (float)config.preemphasis * 1.0e-6f, config.sample_rate, config.preemp_unity_freq);