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comparison: media/libvorbis/lib/vorbis_lpc.c
media/libvorbis/lib/vorbis_lpc.c
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| -1:000000000000 | 0:cafda888adb5 |
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| 1 /******************************************************************** | |
| 2 * * | |
| 3 * THIS FILE IS PART OF THE OggVorbis 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 OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2009 * | |
| 9 * by the Xiph.Org Foundation http://www.xiph.org/ * | |
| 10 * * | |
| 11 ******************************************************************** | |
| 12 | |
| 13 function: LPC low level routines | |
| 14 last mod: $Id: lpc.c 16227 2009-07-08 06:58:46Z xiphmont $ | |
| 15 | |
| 16 ********************************************************************/ | |
| 17 | |
| 18 /* Some of these routines (autocorrelator, LPC coefficient estimator) | |
| 19 are derived from code written by Jutta Degener and Carsten Bormann; | |
| 20 thus we include their copyright below. The entirety of this file | |
| 21 is freely redistributable on the condition that both of these | |
| 22 copyright notices are preserved without modification. */ | |
| 23 | |
| 24 /* Preserved Copyright: *********************************************/ | |
| 25 | |
| 26 /* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann, | |
| 27 Technische Universita"t Berlin | |
| 28 | |
| 29 Any use of this software is permitted provided that this notice is not | |
| 30 removed and that neither the authors nor the Technische Universita"t | |
| 31 Berlin are deemed to have made any representations as to the | |
| 32 suitability of this software for any purpose nor are held responsible | |
| 33 for any defects of this software. THERE IS ABSOLUTELY NO WARRANTY FOR | |
| 34 THIS SOFTWARE. | |
| 35 | |
| 36 As a matter of courtesy, the authors request to be informed about uses | |
| 37 this software has found, about bugs in this software, and about any | |
| 38 improvements that may be of general interest. | |
| 39 | |
| 40 Berlin, 28.11.1994 | |
| 41 Jutta Degener | |
| 42 Carsten Bormann | |
| 43 | |
| 44 *********************************************************************/ | |
| 45 | |
| 46 #include <stdlib.h> | |
| 47 #include <string.h> | |
| 48 #include <math.h> | |
| 49 #include "os.h" | |
| 50 #include "smallft.h" | |
| 51 #include "lpc.h" | |
| 52 #include "scales.h" | |
| 53 #include "misc.h" | |
| 54 | |
| 55 /* Autocorrelation LPC coeff generation algorithm invented by | |
| 56 N. Levinson in 1947, modified by J. Durbin in 1959. */ | |
| 57 | |
| 58 /* Input : n elements of time doamin data | |
| 59 Output: m lpc coefficients, excitation energy */ | |
| 60 | |
| 61 float vorbis_lpc_from_data(float *data,float *lpci,int n,int m){ | |
| 62 double *aut=alloca(sizeof(*aut)*(m+1)); | |
| 63 double *lpc=alloca(sizeof(*lpc)*(m)); | |
| 64 double error; | |
| 65 double epsilon; | |
| 66 int i,j; | |
| 67 | |
| 68 /* autocorrelation, p+1 lag coefficients */ | |
| 69 j=m+1; | |
| 70 while(j--){ | |
| 71 double d=0; /* double needed for accumulator depth */ | |
| 72 for(i=j;i<n;i++)d+=(double)data[i]*data[i-j]; | |
| 73 aut[j]=d; | |
| 74 } | |
| 75 | |
| 76 /* Generate lpc coefficients from autocorr values */ | |
| 77 | |
| 78 /* set our noise floor to about -100dB */ | |
| 79 error=aut[0] * (1. + 1e-10); | |
| 80 epsilon=1e-9*aut[0]+1e-10; | |
| 81 | |
| 82 for(i=0;i<m;i++){ | |
| 83 double r= -aut[i+1]; | |
| 84 | |
| 85 if(error<epsilon){ | |
| 86 memset(lpc+i,0,(m-i)*sizeof(*lpc)); | |
| 87 goto done; | |
| 88 } | |
| 89 | |
| 90 /* Sum up this iteration's reflection coefficient; note that in | |
| 91 Vorbis we don't save it. If anyone wants to recycle this code | |
| 92 and needs reflection coefficients, save the results of 'r' from | |
| 93 each iteration. */ | |
| 94 | |
| 95 for(j=0;j<i;j++)r-=lpc[j]*aut[i-j]; | |
| 96 r/=error; | |
| 97 | |
| 98 /* Update LPC coefficients and total error */ | |
| 99 | |
| 100 lpc[i]=r; | |
| 101 for(j=0;j<i/2;j++){ | |
| 102 double tmp=lpc[j]; | |
| 103 | |
| 104 lpc[j]+=r*lpc[i-1-j]; | |
| 105 lpc[i-1-j]+=r*tmp; | |
| 106 } | |
| 107 if(i&1)lpc[j]+=lpc[j]*r; | |
| 108 | |
| 109 error*=1.-r*r; | |
| 110 | |
| 111 } | |
| 112 | |
| 113 done: | |
| 114 | |
| 115 /* slightly damp the filter */ | |
| 116 { | |
| 117 double g = .99; | |
| 118 double damp = g; | |
| 119 for(j=0;j<m;j++){ | |
| 120 lpc[j]*=damp; | |
| 121 damp*=g; | |
| 122 } | |
| 123 } | |
| 124 | |
| 125 for(j=0;j<m;j++)lpci[j]=(float)lpc[j]; | |
| 126 | |
| 127 /* we need the error value to know how big an impulse to hit the | |
| 128 filter with later */ | |
| 129 | |
| 130 return error; | |
| 131 } | |
| 132 | |
| 133 void vorbis_lpc_predict(float *coeff,float *prime,int m, | |
| 134 float *data,long n){ | |
| 135 | |
| 136 /* in: coeff[0...m-1] LPC coefficients | |
| 137 prime[0...m-1] initial values (allocated size of n+m-1) | |
| 138 out: data[0...n-1] data samples */ | |
| 139 | |
| 140 long i,j,o,p; | |
| 141 float y; | |
| 142 float *work=alloca(sizeof(*work)*(m+n)); | |
| 143 | |
| 144 if(!prime) | |
| 145 for(i=0;i<m;i++) | |
| 146 work[i]=0.f; | |
| 147 else | |
| 148 for(i=0;i<m;i++) | |
| 149 work[i]=prime[i]; | |
| 150 | |
| 151 for(i=0;i<n;i++){ | |
| 152 y=0; | |
| 153 o=i; | |
| 154 p=m; | |
| 155 for(j=0;j<m;j++) | |
| 156 y-=work[o++]*coeff[--p]; | |
| 157 | |
| 158 data[i]=work[o]=y; | |
| 159 } | |
| 160 } |
