bs412 knee

filter/bs412.c

@@ -9,32 +9,36 @@ inline float power_to_dbr(float power, float ref) {
     return 10*log10f(power / ref);
 }
 
-void init_bs412(BS412Compressor* comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, uint32_t sample_rate) {
+void init_bs412(BS412Compressor* comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, float knee_db, uint32_t sample_rate) {
-	comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation); // 0 dbr is a signal which generates a deviation of 19 khz
+	comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation);
 	comp->avg_power = 0.0f;
     comp->alpha = 1.0f / (BS412_TIME * sample_rate);
 	comp->sample_rate = sample_rate;
 	comp->attack = expf(-1.0f / (attack * sample_rate));
 	comp->release = expf(-1.0f / (release * sample_rate));
-	comp->target = comp->reference * powf(10.0f, target_power / 10.0f);;
+	comp->target = comp->reference * powf(10.0f, target_power / 10.0f);
+	comp->target_dbr = power_to_dbr(comp->target, comp->reference);
 	comp->gain = 1.0f;
 	comp->can_compress = 0;
 	comp->second_counter = 0;
 	comp->max_gain = max_gain;
 	comp->gate_threshold = comp->reference * powf(10.0f, gate / 10.0f);
+	comp->knee_db = knee_db; // e.g. 6.0f — width in dB around target on each side
 	comp->init = true;
 	#ifdef BS412_DEBUG
 	debug_printf("Initialized MPX power measurement with sample rate: %d\n", sample_rate);
 	#endif
 }
 
-void reinit_bs412(BS412Compressor* comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate) {
+void reinit_bs412(BS412Compressor* comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, float knee_db) {
-	comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation); // 0 dbr is a signal which generates a deviation of 19 khz
+	comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation);
-	comp->target = comp->reference * powf(10.0f, target_power / 10.0f);;
+	comp->target = comp->reference * powf(10.0f, target_power / 10.0f);
+	comp->target_dbr = power_to_dbr(comp->target, comp->reference);
 	comp->gate_threshold = comp->reference * powf(10.0f, gate / 10.0f);
 	comp->attack = expf(-1.0f / (attack * comp->sample_rate));
 	comp->release = expf(-1.0f / (release * comp->sample_rate));
 	comp->max_gain = max_gain;
+	comp->knee_db = knee_db;
 }
 
 float bs412_compress(BS412Compressor* comp, float audio, float sample_mpx, float* mpx_power) {
@@ -63,17 +67,36 @@ float bs412_compress(BS412Compressor* comp, float audio, float sample_mpx, float
 
 	float safe_power = fmaxf(comp->avg_power, 1e-12f);
 	float target_gain = sqrtf(comp->target / safe_power);
-	if (comp->avg_power > comp->target)
+
-		comp->gain = comp->attack * comp->gain + (1.0f - comp->attack) * target_gain;
+	// Soft knee: blend between unity gain and target_gain based on how far
-	else
+	// we are inside the knee region. knee_db is the half-width on each side
-		comp->gain = comp->release * comp->gain + (1.0f - comp->release) * target_gain;
+	// of the target. Below (target - knee), gain tracks freely toward max_gain.
-	
+	// Above (target + knee), full compression applies. In between, it blends.
+	float level_dbr = power_to_dbr(comp->avg_power, comp->reference);
+	float half_knee = comp->knee_db * 0.5f;
+	float dist = level_dbr - comp->target_dbr; // negative = below target, positive = above
+
+	float knee_blend;
+	if (dist <= -half_knee) knee_blend = 0.0f; // well below target — don't pull gain toward target
+	else if (dist >= half_knee) knee_blend = 1.0f; // well above target — full compression
+	else {
+		// Smooth cubic ramp: 0→1 over the knee width
+		float t = (dist + half_knee) / comp->knee_db; // 0..1
+		knee_blend = t * t * (3.0f - 2.0f * t);       // smoothstep
+	}
+
+	// The effective target_gain for the smoothed region blends between
+	// current gain (no correction) and the true target_gain.
+	float blended_target = comp->gain + knee_blend * (target_gain - comp->gain);
+
+	float coeff = (comp->avg_power > comp->target) ? comp->attack : comp->release;
+	comp->gain = coeff * comp->gain + (1.0f - coeff) * blended_target;
 	comp->gain = CLAMP(comp->gain, 0.01f, comp->max_gain);
 
 	comp->sample_counter++;
 
-	if(mpx_power != NULL) *mpx_power = power_to_dbr(comp->avg_power, comp->reference);
+	if(mpx_power != NULL) *mpx_power = level_dbr;
 
 	if(comp->can_compress) return output_sample;
 	return combined;
-}
+}

filter/bs412.h

@@ -17,6 +17,7 @@ typedef struct {
 	uint32_t sample_rate;
 	uint32_t sample_counter;
 	float target;
+	float target_dbr;
 	float attack;
 	float release;
 	float max_gain;
@@ -28,8 +29,9 @@ typedef struct {
 	float last_output;
 	float gate_threshold;
 	bool init;
+	float knee_db;
 } BS412Compressor;
 
-void init_bs412(BS412Compressor *comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, uint32_t sample_rate);
+void init_bs412(BS412Compressor *comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, float knee_db, uint32_t sample_rate);
-void reinit_bs412(BS412Compressor *comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate);
+void reinit_bs412(BS412Compressor *comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate, float knee_db);
 float bs412_compress(BS412Compressor *comp, float audio, float sample_mpx, float* mpx_power);

src/fm95.c

@@ -3,7 +3,7 @@
 #include "../inih/ini.h"
 #include <stdbool.h>
 
-#define DEFAULT_INI_PATH "/etc/fm95.conf"
+#define DEFAULT_INI_PATH "/etc/fm95/fm95.conf"
 
 #define buffer_maxlength 99960
 #define buffer_tlength_fragsize 99960
@@ -67,6 +67,7 @@ typedef struct {
 	float bs412_release;
 	float bs412_max;
 	float bs412_gate;
+	float bs412_knee;
 	float lpf_cutoff;
 } FM95_Config;
 
@@ -221,7 +222,7 @@ int run_fm95(FM95_Config* config, FM95_Runtime* runtime, FM95_RunResult* result)
 				l *= agc_gain;
 				r *= agc_gain;
 				temp_result.agc_gain = agc_gain;
-			}
+			} else temp_result.agc_gain = 0.0f;
 
 			float mod_l, mod_r;
 
@@ -334,6 +335,7 @@ static int config_handler(void* user, const char* section, const char* name, con
 	else if(MATCH("fm95", "bs412_release")) pconfig->bs412_release = strtof(value, NULL);
 	else if(MATCH("fm95", "bs412_max")) pconfig->bs412_max = strtof(value, NULL);
 	else if(MATCH("fm95", "bs412_gate")) pconfig->bs412_gate = strtof(value, NULL);
+	else if(MATCH("fm95", "bs412_knee")) pconfig->bs412_knee = strtof(value, NULL);
 	else if(MATCH("advanced", "lpf_order")) pconfig->lpf_order = atoi(value);
 	else if(MATCH("advanced", "stereo_ssb")) pconfig->stereo_ssb = atoi(value);
 	else if(MATCH("advanced", "preemp_unity")) pconfig->preemp_unity_freq = strtof(value, NULL);
@@ -444,8 +446,8 @@ void init_runtime(FM95_Runtime* runtime, const FM95_Config config) {
 	}
 
 	if(runtime->bs412.init == true && (runtime->bs412.sample_rate == config.sample_rate)) {
-		reinit_bs412(&runtime->bs412, config.mpx_deviation, config.mpx_power, config.bs412_attack, config.bs412_release, config.bs412_max, config.bs412_gate);
+		reinit_bs412(&runtime->bs412, config.mpx_deviation, config.mpx_power, config.bs412_attack, config.bs412_release, config.bs412_max, config.bs412_gate, config.bs412_knee);
-	} else init_bs412(&runtime->bs412, config.mpx_deviation, config.mpx_power, config.bs412_attack, config.bs412_release, config.bs412_max, config.bs412_gate, config.sample_rate);
+	} else init_bs412(&runtime->bs412, config.mpx_deviation, config.mpx_power, config.bs412_attack, config.bs412_release, config.bs412_max, config.bs412_gate, config.bs412_knee, config.sample_rate);
 	init_stereo_encoder(&runtime->stencode, config.stereo_ssb, 4.0f, &runtime->osc, config.volumes.audio, config.volumes.pilot);
 
 	float last_gain = 0.0f;
@@ -560,6 +562,16 @@ static void *handle_client(ipc_client_arg_t *arg) {
 				to_run = 0;
 				to_reload = 1;
 				break;
+			case 110:
+				// Set BS412 gate
+				memcpy(&val, buf + 1, sizeof(float));
+				data->runtime->bs412.knee_db = val;
+				reply = 0;
+				break;
+			case 0xfe:
+				// Fetch config
+        		send(fd, data->config, sizeof(FM95_Config), 0);
+				break;
 			case 0xff:
 				// Fetch data
         		send(fd, data->run_result, sizeof(FM95_RunResult), 0);
@@ -617,6 +629,7 @@ int main(int argc, char **argv) {
 		.bs412_release = 0.025f,
 		.bs412_max = 2.82f,
 		.bs412_gate = -20.0f,
+		.bs412_knee = 4.0f,
 		.lpf_cutoff = 15000.0f,
 	};