third_party/soloud_speech/resonator.cpp

   1 #include <math.h>
   2 #include "resonator.h"
   3
   4 #ifndef PI
   5 #define PI 3.1415926535897932384626433832795f
   6 #endif
   7
   8 /* Convert formant freqencies and bandwidth into resonator difference equation coefficents
   9         */
  10 void resonator::initResonator(
  11         int aFrequency,                       /* Frequency of resonator in Hz  */
  12         int aBandwidth,                      /* Bandwidth of resonator in Hz  */
  13         int aSamplerate)
  14 {
  15         float arg = (-PI / aSamplerate) * aBandwidth;
  16         float r = (float)exp(arg);
  17         mC = -(r * r);
  18         arg = (-2.0f * PI / aSamplerate) * aFrequency;
  19         mB = r * (float)cos(arg) * 2.0f;
  20         mA = 1.0f - mB - mC;
  21 }
  22
  23 /* Convert formant freqencies and bandwidth into anti-resonator difference equation constants
  24         */
  25 void resonator::initAntiresonator(
  26         int aFrequency,                       /* Frequency of resonator in Hz  */
  27         int aBandwidth,                      /* Bandwidth of resonator in Hz  */
  28         int aSamplerate)
  29 {
  30         initResonator(aFrequency, aBandwidth, aSamplerate); /* First compute ordinary resonator coefficients */
  31         /* Now convert to antiresonator coefficients */
  32         mA = 1.0f / mA;             /* a'=  1/a */
  33         mB *= -mA;                  /* b'= -b/a */
  34         mC *= -mA;                  /* c'= -c/a */
  35 }
  36
  37 /* Generic resonator function */
  38 float resonator::resonate(float input)
  39 {
  40         float x = mA * input + mB * mP1 + mC * mP2;
  41         mP2 = mP1;
  42         mP1 = x;
  43         return x;
  44 }
  45
  46 /* Generic anti-resonator function
  47         Same as resonator except that a,b,c need to be set with initAntiresonator()
  48         and we save inputs in p1/p2 rather than outputs.
  49         There is currently only one of these - "mNasalZero"
  50 */
  51 /*  Output = (mNasalZero.a * input) + (mNasalZero.b * oldin1) + (mNasalZero.c * oldin2) */
  52
  53 float resonator::antiresonate(float input)
  54 {
  55         float x = mA * input + mB * mP1 + mC * mP2;
  56         mP2 = mP1;
  57         mP1 = input;
  58         return x;
  59 }
  60
  61 resonator::resonator()
  62 {
  63         mA = mB = mC = mP1 = mP2 = 0;
  64 }
  65
  66 resonator::~resonator()
  67 {
  68 }
  69
  70 void resonator::setGain(float aG)
  71 {
  72         mA *= aG;
  73 }
  74