try another bs412 compressor implementation

filter/bs412.c

@@ -11,16 +11,20 @@ inline float deviation_to_dbr(float deviation) {
 	return 10.0f * (log2f(deviation) - LOG2_19000) * 0.30103f;
 }
 
-void init_modulation_power_measure(MPXPowerMeasurement* mpx, int sample_rate) {
+void init_bs412(BS412Compressor* mpx, float target_power, float attack, float release, int sample_rate) {
 	mpx->sample_counter = 0;
 	mpx->sample = 0;
 	mpx->sample_rate = sample_rate;
+	mpx->attack = expf(-1.0f / (attack * sample_rate));
+	mpx->release = expf(-1.0f / (release * sample_rate));
+	mpx->target = target_power;
+	mpx->gain = 1.0f;
 	#ifdef BS412_DEBUG
 	debug_printf("Initialized MPX power measurement with sample rate: %d\n", sample_rate);
 	#endif
 }
 
-float measure_mpx(MPXPowerMeasurement* mpx, float deviation) {
+float bs412_compress(BS412Compressor* mpx, float deviation) {
 	mpx->sample += deviation * deviation; // rmS
 	mpx->sample_counter++;
 
@@ -42,5 +46,12 @@ float measure_mpx(MPXPowerMeasurement* mpx, float deviation) {
 		mpx->sample_counter = 1;
 	}
 
-	return modulation_power;
+	float gain_target = powf(10.0f, (mpx->target - modulation_power) / 20.0f); // dB to linear
+	if (gain_target > mpx->gain)
+		mpx->gain = mpx->gain * mpx->attack + (1.0f - mpx->attack) * gain_target;
+	else
+		mpx->gain = mpx->gain * mpx->release + (1.0f - mpx->release) * gain_target;
+
+
+	return deviation*mpx->gain;
 }

filter/bs412.h

@@ -13,11 +13,15 @@ typedef struct
 {
 	int sample_counter;
 	int sample_rate;
+	float target;
+	float attack;
+	float release;
+	float gain;
 	double sample;
-} MPXPowerMeasurement;
+} BS412Compressor;
 
 float dbr_to_deviation(float dbr);
 float deviation_to_dbr(float deviation);
 
-void init_modulation_power_measure(MPXPowerMeasurement *mpx, int sample_rate);
+void init_bs412(BS412Compressor *mpx, float target_power, float attack, float release, int sample_rate);
-float measure_mpx(MPXPowerMeasurement *mpx, float deviation);
+float bs412_compress(BS412Compressor *mpx, float deviation);

src/fm95.c

@@ -166,8 +166,8 @@ int run_fm95(const FM95_Config config, FM95_Runtime* runtime) {
 	init_preemphasis(&preemp_l, config.preemphasis, config.sample_rate, config.preemp_unity_freq);
 	init_preemphasis(&preemp_r, config.preemphasis, config.sample_rate, config.preemp_unity_freq);
 
-	MPXPowerMeasurement power;
+	BS412Compressor bs412;
-	init_modulation_power_measure(&power, config.sample_rate);
+	init_bs412(&bs412, config.mpx_power, config.bs412_attack, config.bs412_release, config.sample_rate);
 
 	TiltCorrectionFilter tilter;
 	tilt_init(&tilter, config.tilt);
@@ -175,10 +175,6 @@ int run_fm95(const FM95_Config config, FM95_Runtime* runtime) {
 	StereoEncoder stencode;
 	init_stereo_encoder(&stencode, 4.0f, &osc, (config.stereo == 2), config.volumes.mono, config.volumes.pilot, config.volumes.stereo);
 
-	float bs412_audio_gain = 1.0f;
-	float bs412_attack_alpha = expf(-1.0f / (config.bs412_attack * config.sample_rate));
-	float bs412_release_alpha = expf(-1.0f / (config.bs412_release * config.sample_rate));
-
 	AGC agc;
 	initAGC(&agc, config.sample_rate, config.agc_target, config.agc_min, config.agc_max, config.agc_attack, config.agc_release);
 
@@ -236,21 +232,7 @@ int run_fm95(const FM95_Config config, FM95_Runtime* runtime) {
 				}
 			}
 
-			float mpx_power = measure_mpx(&power, mpx * config.mpx_deviation);
+			mpx = bs412_compress(&bs412, mpx*config.mpx_deviation);
-			if (mpx_power > config.mpx_power) {
-				float excess_power = mpx_power - config.mpx_power;
-				
-				if (excess_power > 0.0f && excess_power < 10.0f) {
-					float target_gain = dbr_to_deviation(-excess_power) / config.mpx_deviation;
-					
-					target_gain = fmaxf(target_gain, 0.1f);
-					target_gain = fminf(target_gain, 1.0f);
-					
-					bs412_audio_gain = bs412_attack_alpha * bs412_audio_gain + (1 - bs412_attack_alpha) * target_gain;
-				}
-			} else bs412_audio_gain = fminf(1.0f, bs412_release_alpha * bs412_audio_gain + (1 - bs412_release_alpha) * 1.0f);
-
-			mpx *= bs412_audio_gain;
 			
 			output[i] = hard_clip(tilt(&tilter, (mpx_in[i]+mpx))*config.master_volume, 1.0); // Ensure peak deviation of 75 khz, assuming we're calibrated correctly (lower)
 			advance_oscillator(&osc);