agc?

lib/filters.h

@@ -7,12 +7,6 @@
 #include "optimization.h"
 #include "oscillator.h"
 
-#if USE_NEON
-#define LPF_ORDER 20 // neon has to have divisable by 4
-#else
-#define LPF_ORDER 10
-#endif
-
 typedef struct
 {
 	float alpha;

lib/gain_control.c

@@ -0,0 +1,40 @@
+#include "gain_control.h"
+
+void initAGC(AGC* agc, int sampleRate, float targetLevel, float minGain, float maxGain, float attackTime, float releaseTime) {
+	agc->sampleRate = sampleRate;
+	agc->targetLevel = targetLevel;
+	agc->minGain = minGain;
+	agc->maxGain = maxGain;
+	agc->attackTime = attackTime;
+	agc->releaseTime = releaseTime;
+
+	agc->attackCoef = expf(-1.0f / (sampleRate * attackTime));
+	agc->releaseCoef = expf(-1.0f / (sampleRate * releaseTime));
+
+	agc->currentGain = 1.0f;
+	agc->currentLevel = 0.0f;
+
+	agc->rms_buffer = 0.0f;
+}
+
+float process_agc_stereo(AGC* agc, float left, float right, float *right_out) {
+	float sample = (left+right)/2;
+
+	float x2 = sample * sample;
+
+	float rmsAlpha = expf(-1.0f / (agc->sampleRate * 0.04));
+	agc->rms_buffer = rmsAlpha * agc->rms_buffer + (1.0f - rmsAlpha) * x2;
+	float instantLevel = sqrtf(agc->rms_buffer);
+
+	float alpha = (instantLevel > agc->currentLevel) ? agc->attackCoef : agc->releaseCoef;
+	agc->currentLevel = alpha * agc->currentLevel + (1.0f - alpha) * instantLevel;
+
+	float desiredGain = agc->targetLevel / fmaxf(agc->currentLevel, 1e-10f);
+	desiredGain = fminf(fmaxf(desiredGain, agc->minGain), agc->maxGain);
+
+	float gainAlpha = (desiredGain > agc->currentGain) ? agc->attackCoef : agc->releaseCoef;
+	agc->currentGain = gainAlpha * agc->currentGain + (1.0f - gainAlpha) * desiredGain;
+
+	*right_out = right * agc->currentGain;
+	return left * agc->currentGain;
+}

lib/gain_control.h

@@ -0,0 +1,22 @@
+#pragma once
+#include <math.h>
+
+typedef struct {
+	float targetLevel;
+	float maxGain;
+	float minGain;
+	float attackTime;
+	float releaseTime;
+
+	float currentGain;
+	float currentLevel;
+
+	int sampleRate;
+	float attackCoef;
+	float releaseCoef;
+
+	float rms_buffer;
+} AGC;
+
+void initAGC(AGC* agc, int sampleRate, float targetLevel, float minGain, float maxGain, float attackTime, float releaseTime);
+float process_agc_stereo(AGC* agc, float left, float right, float *right_out);

src/fm95.c

@@ -21,6 +21,7 @@
 #include "../lib/fm_modulator.h"
 #include "../lib/optimization.h"
 #include "../lib/bs412.h"
+#include "../lib/gain_control.h"
 
 #define DEFAULT_SAMPLE_RATE 192000
 
@@ -453,6 +454,10 @@ int main(int argc, char **argv) {
 	MPXPowerMeasurement mpx_only_power;
 	init_modulation_power_measure(&mpx_only_power, sample_rate);
 
+	AGC agc;
+	void initAGC(AGC* agc, int sampleRate, float targetLevel, float minGain, float maxGain, float attackTime, float releaseTime);
+	initAGC(&agc, sample_rate, 0.707f, 0.25f, 2.5f, 0.01f, 0.4f);
+
 	signal(SIGINT, stop);
 	signal(SIGTERM, stop);
 
@@ -512,6 +517,7 @@ int main(int argc, char **argv) {
 
 			float ready_l = apply_preemphasis(&preemp_l, l_in);
 			float ready_r = apply_preemphasis(&preemp_r, r_in);
+			ready_l = process_agc_stereo(&agc, ready_l, ready_r, &ready_r);
 			ready_l = hard_clip(ready_l*audio_volume, clipper_threshold);
 			ready_r = hard_clip(ready_r*audio_volume, clipper_threshold);