Line data    Source code

       1              : #pragma once
       2              : 
       3              : #include "common.h"
       4              : #include <cmath>
       5              : 
       6              : namespace Amplitron {
       7              : 
       8              : /**
       9              :  * Attack/release envelope follower.
      10              :  * Used by Compressor, NoiseGate, WahPedal, and AmpSimulator.
      11              :  */
      12          198 : struct EnvelopeFollower {
      13          132 :     float envelope = 0.0f;
      14              : 
      15              :     /**
      16              :      * Compute attack/release coefficients from time constants.
      17              :      * @param ms       Time in milliseconds.
      18              :      * @param sr       Sample rate.
      19              :      * @return One-pole coefficient (pass to process()).
      20              :      */
      21          685 :     static float time_to_coeff(float ms, int sr) {
      22          685 :         return std::exp(-1.0f / (sr * ms * 0.001f));
      23              :     }
      24              : 
      25              :     /**
      26              :      * Process one sample and return the new envelope value.
      27              :      * Coefficients are in "smoothing" form: higher = slower.
      28              :      */
      29        24000 :     float process(float input, float attack_coeff, float release_coeff) {
      30        24000 :         float abs_in = std::fabs(input);
      31        24000 :         float coeff = (abs_in > envelope) ? attack_coeff : release_coeff;
      32        24000 :         envelope = coeff * envelope + (1.0f - coeff) * abs_in;
      33        24000 :         return envelope;
      34              :     }
      35              : 
      36              :     /**
      37              :      * Alternative form matching the Compressor's convention:
      38              :      * coeff = 1 - exp(...), applied as: envelope += coeff * (abs - envelope)
      39              :      */
      40       238080 :     float process_additive(float input, float attack_coeff, float release_coeff) {
      41       238080 :         float abs_in = std::fabs(input);
      42       193024 :         float coeff = (abs_in > envelope) ? (1.0f - attack_coeff) : (1.0f - release_coeff);
      43       238080 :         envelope += coeff * (abs_in - envelope);
      44       238080 :         return envelope;
      45              :     }
      46              : 
      47          249 :     void reset() { envelope = 0.0f; }
      48              : };
      49              : 
      50              : } // namespace Amplitron