libs/qm-dsp/base/Pitch.cpp

   1 /* -*- c-basic-offset: 4 indent-tabs-mode: nil -*-  vi:set ts=8 sts=4 sw=4: */
   2
   3 /*
   4     QM DSP library
   5     Centre for Digital Music, Queen Mary, University of London.
   6     This file Copyright 2006 Chris Cannam.
   7
   8     This program is free software; you can redistribute it and/or
   9     modify it under the terms of the GNU General Public License as
  10     published by the Free Software Foundation; either version 2 of the
  11     License, or (at your option) any later version.  See the file
  12     COPYING included with this distribution for more information.
  13 */
  14
  15 #include "Pitch.h"
  16
  17 #include <math.h>
  18
  19 float
  20 Pitch::getFrequencyForPitch(int midiPitch,
  21                             float centsOffset,
  22                             float concertA)
  23 {
  24     float p = float(midiPitch) + (centsOffset / 100);
  25     return concertA * powf(2.0, (p - 69.0) / 12.0);
  26 }
  27
  28 int
  29 Pitch::getPitchForFrequency(float frequency,
  30                             float *centsOffsetReturn,
  31                             float concertA)
  32 {
  33     float p = 12.0 * (log(frequency / (concertA / 2.0)) / log(2.0)) + 57.0;
  34
  35     int midiPitch = int(p + 0.00001);
  36     float centsOffset = (p - midiPitch) * 100.0;
  37
  38     if (centsOffset >= 50.0) {
  39         midiPitch = midiPitch + 1;
  40         centsOffset = -(100.0 - centsOffset);
  41     }
  42
  43     if (centsOffsetReturn) *centsOffsetReturn = centsOffset;
  44     return midiPitch;
  45 }
  46