Line data    Source code

       1              : #include "audio/effects/compressor.h"
       2              : #include "audio/effects/effect_factory.h"
       3              : 
       4              : namespace Amplitron {
       5              : 
       6            2 : static EffectRegistrar<Compressor> reg("Compressor");
       7              : 
       8           88 : Compressor::Compressor() {
       9          286 :     params_ = {
      10           66 :         {"Threshold", -20.0f, -60.0f,  0.0f, -20.0f, "dB", "Signal level at which compression begins. Signals above this level will be reduced in volume."},
      11           22 :         {"Ratio",       4.0f,   1.0f, 20.0f,   4.0f, ":1", "How strongly to reduce peaks that exceed the threshold. Higher values create a more squashed sound."},
      12           22 :         {"Attack",      5.0f,   0.1f, 50.0f,   5.0f, "ms", "How quickly the compressor reacts to peaks. Fast attack clamps down immediately, slow allows pick transients through."},
      13           22 :         {"Release",   100.0f,  10.0f, 500.0f, 100.0f, "ms", "How quickly the compressor stops reducing volume after the signal drops below threshold."},
      14           22 :         {"Makeup",      0.0f,   0.0f, 30.0f,   0.0f, "dB", "Gain boost applied after compression to compensate for the volume lost during peak reduction."},
      15          286 :     };
      16          132 : }
      17              : 
      18           36 : void Compressor::process(float* buffer, int num_samples) {
      19           36 :     if (!enabled_) return;
      20              : 
      21           36 :     float threshold_db = params_[0].value;
      22           36 :     float ratio = params_[1].value;
      23           36 :     float attack_ms = params_[2].value;
      24           36 :     float release_ms = params_[3].value;
      25           36 :     float makeup = db_to_linear(params_[4].value);
      26              : 
      27              :     // Parameter smoothing (anti-zipper) — keep short enough to reduce zipper noise
      28              :     // while limiting lag in fast attack/release settings.
      29           36 :     const float alpha = 1.0f - std::exp(-1.0f / (sample_rate_ * 0.002f)); // 2 ms
      30           36 :     smoothed_attack_ms_  += alpha * (attack_ms  - smoothed_attack_ms_);
      31           36 :     smoothed_release_ms_ += alpha * (release_ms - smoothed_release_ms_);
      32              : 
      33           36 :     float attack_coeff = EnvelopeFollower::time_to_coeff(smoothed_attack_ms_, sample_rate_);
      34           36 :     float release_coeff = EnvelopeFollower::time_to_coeff(smoothed_release_ms_, sample_rate_);
      35              : 
      36        35364 :     for (int i = 0; i < num_samples; ++i) {
      37        35328 :         float envelope = env_.process_additive(buffer[i], attack_coeff, release_coeff);
      38              : 
      39        35328 :         float env_db = linear_to_db(envelope);
      40        35328 :         float gain_db = 0.0f;
      41        35328 :         if (env_db > threshold_db) {
      42        33759 :             gain_db = (threshold_db - env_db) * (1.0f - 1.0f / ratio);
      43        11253 :         }
      44              : 
      45        35328 :         float gain = db_to_linear(gain_db) * makeup;
      46        35328 :         buffer[i] *= gain;
      47        11776 :     }
      48           12 : }
      49              : 
      50           57 : void Compressor::reset() {
      51           57 :     env_.reset();
      52           57 : }
      53              : 
      54              : } // namespace Amplitron