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bs412 knee

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kuba
2026-05-10 17:42:47 +02:00
parent ae8ee99342
commit 3fd82cc1ed
3 changed files with 57 additions and 19 deletions
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filter/bs412.c
+36 -13
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@@ -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) {
comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation); // 0 dbr is a signal which generates a deviation of 19 khz
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);
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) {
comp->reference = (19000.0f / mpx_deviation) * (19000.0f / mpx_deviation); // 0 dbr is a signal which generates a deviation of 19 khz
comp->target = comp->reference * powf(10.0f, target_power / 10.0f);;
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);
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;
else
comp->gain = comp->release * comp->gain + (1.0f - comp->release) * target_gain;
// Soft knee: blend between unity gain and target_gain based on how far
// we are inside the knee region. knee_db is the half-width on each side
// 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
+4 -2
View File
@@ -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 reinit_bs412(BS412Compressor *comp, uint32_t mpx_deviation, float target_power, float attack, float release, float max_gain, float gate);
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, float knee_db);
float bs412_compress(BS412Compressor *comp, float audio, float sample_mpx, float* mpx_power);