vrshoot
view libs/vorbis/lpc.c @ 1:e7ca128b8713
looks nice :)
| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Sun, 02 Feb 2014 00:35:22 +0200 |
| parents | |
| children |
line source
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 ********************************************************************
13 function: LPC low level routines
14 last mod: $Id: lpc.c 16227 2009-07-08 06:58:46Z xiphmont $
16 ********************************************************************/
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. */
24 /* Preserved Copyright: *********************************************/
26 /* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann,
27 Technische Universita"t Berlin
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.
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.
40 Berlin, 28.11.1994
41 Jutta Degener
42 Carsten Bormann
44 *********************************************************************/
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"
55 /* Autocorrelation LPC coeff generation algorithm invented by
56 N. Levinson in 1947, modified by J. Durbin in 1959. */
58 /* Input : n elements of time doamin data
59 Output: m lpc coefficients, excitation energy */
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;
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 }
76 /* Generate lpc coefficients from autocorr values */
78 /* set our noise floor to about -100dB */
79 error=aut[0] * (1. + 1e-10);
80 epsilon=1e-9*aut[0]+1e-10;
82 for(i=0;i<m;i++){
83 double r= -aut[i+1];
85 if(error<epsilon){
86 memset(lpc+i,0,(m-i)*sizeof(*lpc));
87 goto done;
88 }
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. */
95 for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];
96 r/=error;
98 /* Update LPC coefficients and total error */
100 lpc[i]=r;
101 for(j=0;j<i/2;j++){
102 double tmp=lpc[j];
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;
109 error*=1.-r*r;
111 }
113 done:
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 }
125 for(j=0;j<m;j++)lpci[j]=(float)lpc[j];
127 /* we need the error value to know how big an impulse to hit the
128 filter with later */
130 return error;
131 }
133 void vorbis_lpc_predict(float *coeff,float *prime,int m,
134 float *data,long n){
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 */
140 long i,j,o,p;
141 float y;
142 float *work=alloca(sizeof(*work)*(m+n));
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];
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];
158 data[i]=work[o]=y;
159 }
160 }