1 /********************************************************************
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. *
8 * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2009 *
9 * by the Xiph.Org Foundation http://www.xiph.org/ *
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
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.
44 *********************************************************************/
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));
68 /* autocorrelation, p+1 lag coefficients */
71 double d=0; /* double needed for accumulator depth */
72 for(i=j;i<n;i++)d+=(double)data[i]*data[i-j];
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;
86 memset(lpc+i,0,(m-i)*sizeof(*lpc));
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
95 for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];
98 /* Update LPC coefficients and total error */
104 lpc[j]+=r*lpc[i-1-j];
107 if(i&1)lpc[j]+=lpc[j]*r;
115 /* slightly damp the filter */
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
133 void vorbis_lpc_predict(float *coeff,float *prime,int m,
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 */
142 float *work=alloca(sizeof(*work)*(m+n));
156 y-=work[o++]*coeff[--p];