libs/ardour/interpolation.cc

   1 #include <stdint.h>
   2 #include "ardour/interpolation.h"
   3
   4 using namespace ARDOUR;
   5
   6 nframes_t
   7 LinearInterpolation::interpolate (nframes_t nframes, Sample *input, Sample *output)
   8 {
   9         // the idea is that when the speed is not 1.0, we have to
  10         // interpolate between samples and then we have to store where we thought we were.
  11         // rather than being at sample N or N+1, we were at N+0.8792922
  12
  13         // index in the input buffers
  14         nframes_t   i = 0;
  15
  16         double acceleration;
  17         double distance = 0.0;
  18
  19         if (_speed != _target_speed) {
  20                 acceleration = _target_speed - _speed;
  21         } else {
  22                 acceleration = 0.0;
  23         }
  24
  25         for (nframes_t outsample = 0; outsample < nframes; ++outsample) {
  26                 i = distance;
  27                 Sample fractional_phase_part = distance - i;
  28
  29                 if (input && output) {
  30                 // Linearly interpolate into the output buffer
  31                         output[outsample] =
  32                                 input[i] * (1.0f - fractional_phase_part) +
  33                                 input[i+1] * fractional_phase_part;
  34                 }
  35                 distance   += _speed + acceleration;
  36         }
  37
  38         i = (distance + 0.5L);
  39         // playback distance
  40         return i;
  41 }