loudness.c

   1 #include "loudness.h"
   2 #include "common.h"
   3 #include <math.h>
   4
   5 loudness_processor loudness_r;
   6 loudness_processor loudness_l;
   7
   8 void _loudness_set_volume(loudness_processor *p, float volume) {
   9   float gain = -(volume - config.loudness_reference_volume_db) * 0.5;
  10   if (gain < 0)
  11     gain = 0;
  12
  13   float Fc = 10.0;
  14   float Q = 0.5;
  15
  16   // Formula from http://www.earlevel.com/main/2011/01/02/biquad-formulas/
  17   float Fs = 44100.0;
  18
  19   float K = tan(M_PI * Fc / Fs);
  20   float V = pow(10.0, gain / 20.0);
  21
  22   float norm = 1 / (1 + 1 / Q * K + K * K);
  23   p->a0 = (1 + V / Q * K + K * K) * norm;
  24   p->a1 = 2 * (K * K - 1) * norm;
  25   p->a2 = (1 - V / Q * K + K * K) * norm;
  26   p->b1 = p->a1;
  27   p->b2 = (1 - 1 / Q * K + K * K) * norm;
  28 }
  29
  30 float loudness_process(loudness_processor *p, float i0) {
  31   float o0 = p->a0 * i0 + p->a1 * p->i1 + p->a2 * p->i2 - p->b1 * p->o1 - p->b2 * p->o2;
  32
  33   p->o2 = p->o1;
  34   p->o1 = o0;
  35
  36   p->i2 = p->i1;
  37   p->i1 = i0;
  38
  39   return o0;
  40 }
  41
  42 void loudness_set_volume(float volume) {
  43   float gain = -(volume - config.loudness_reference_volume_db) * 0.5;
  44   if (gain < 0)
  45     gain = 0;
  46
  47   debug(2, "Volume: %.1f dB - Loudness gain @10Hz: %.1f dB", volume, gain);
  48   _loudness_set_volume(&loudness_l, volume);
  49   _loudness_set_volume(&loudness_r, volume);
  50 }