chirptest/window.c

   1 /********************************************************************
   2  *                                                                  *
   3  * THIS FILE IS PART OF THE OggGhost SOFTWARE CODEC SOURCE CODE.    *
   4  * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS     *
   5  * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
   6  * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING.       *
   7  *                                                                  *
   8  * THE OggGhost SOURCE CODE IS (C) COPYRIGHT 2007-2011              *
   9  * by the Xiph.Org Foundation http://www.xiph.org/                  *
  10  *                                                                  *
  11  ********************************************************************
  12
  13  function: window functions for research code
  14  last mod: $Id$
  15
  16  ********************************************************************/
  17
  18 #define _GNU_SOURCE
  19 #include <math.h>
  20 #include "window.h"
  21
  22 /* A few windows */
  23
  24 /* Not-a-window */
  25 static void rectangle(float *x, int n){
  26   int i;
  27   for(i=0;i<n;i++)
  28     x[i]=1.;
  29 }
  30
  31 /* sine window */
  32 static void sine(float *x, int n){
  33   int i;
  34   float scale = M_PI/n;
  35
  36   for(i=0;i<n;i++){
  37     float i5 = i+.5;
  38     x[i] = sin(scale*i5);
  39   }
  40 }
  41
  42 /* Minimum 4-term Blackman Harris; highest sidelobe = -92dB */
  43 #define A0 .35875f
  44 #define A1 .48829f
  45 #define A2 .14128f
  46 #define A3 .01168f
  47
  48 static void blackmann_harris(float *x, int n){
  49   int i;
  50   float scale = 2*M_PI/n;
  51
  52   for(i=0;i<n;i++){
  53     float i5 = i+.5;
  54     float w = A0 - A1*cos(scale*i5) + A2*cos(scale*i5*2) - A3*cos(scale*i5*3);
  55     x[i] = w;
  56   }
  57 }
  58
  59 /* Good 'ol Hanning window (narrow mainlobe, fast falloff, high sidelobes) */
  60 static void hanning(float *x, int n){
  61   int i;
  62   float scale = 2*M_PI/n;
  63
  64   for(i=0;i<n;i++){
  65     float i5 = i+.5;
  66     x[i] = (.5-.5*cos(scale*i5));
  67   }
  68 }
  69
  70 /* Triangular * gaussian (sidelobeless window) */
  71 #define TGA 1.e-4
  72 #define TGB 21.6
  73 static void tgauss_deep(float *x, int n){
  74   int i;
  75   for(i=0;i<n;i++){
  76     float f = (i+.5-n/2.)/(n/2.);
  77     x[i] = exp(-TGB*pow(f,2)) * pow(1.-fabs(f),TGA);
  78   }
  79 }
  80
  81 static void vorbis(float *d, int n){
  82   int i;
  83   for(i=0;i<n;i++)
  84     d[i] = sin(0.5 * M_PI * sin((i+.5)/n * M_PI)*sin((i+.5)/n * M_PI));
  85 }
  86
  87 static float beta(int n, float alpha){
  88   return cosh (acosh(pow(10,alpha))/(n-1));
  89 }
  90
  91 static double T(double n, double x){
  92   if(fabs(x)<=1){
  93     return cos(n*acos(x));
  94   }else{
  95     return cosh(n*acosh(x));
  96   }
  97 }
  98
  99 /* Dolph-Chebyshev window (a=6., all sidelobes < -120dB) */
 100 static void dolphcheb(float *d, int n){
 101   int i,k;
 102   float a = 6.;
 103   int M=n/2;
 104   int N=M*2;
 105   double b = beta(N,a);
 106
 107   for(i=0;i<n;i++){
 108     double sum=0;
 109     for(k=0;k<M;k++)
 110       sum += (k&1?-1:1)*T(N,b*cos(M_PI*k/N)) * cos (2*i*k*M_PI/N);
 111     sum /= T(N,b);
 112     sum-=.5;
 113     d[i]=sum;
 114   }
 115 }
 116
 117 /* sidelobeless window machine optimized for fast convergence */
 118 static void maxwell1(float *x, int n){
 119   int i;
 120   float scale = 2*M_PI/n;
 121   for(i=0;i<n;i++){
 122     float i5 = i+.5;
 123     x[i] = pow( 119.72981
 124                 - 119.24098*cos(scale*i5)
 125                 + 0.10283622*cos(2*scale*i5)
 126                 + 0.044013144*cos(3*scale*i5)
 127                 + 0.97203713*cos(4*scale*i5),
 128                 1.9730763)/50000.;
 129   }
 130 }
 131
 132 window_bundle window_functions = {
 133   rectangle,
 134   sine,
 135   hanning,
 136   vorbis,
 137   blackmann_harris,
 138   tgauss_deep,
 139   dolphcheb,
 140   maxwell1,
 141 };