159 lines
4.4 KiB
C
159 lines
4.4 KiB
C
/********************************************************************
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* *
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* THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE. *
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* USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS *
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* GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE *
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* IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. *
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* *
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* THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2009 *
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* by the Xiph.Org Foundation http://www.xiph.org/ *
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* *
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********************************************************************
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function: LPC low level routines
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********************************************************************/
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/* Some of these routines (autocorrelator, LPC coefficient estimator)
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are derived from code written by Jutta Degener and Carsten Bormann;
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thus we include their copyright below. The entirety of this file
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is freely redistributable on the condition that both of these
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copyright notices are preserved without modification. */
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/* Preserved Copyright: *********************************************/
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/* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann,
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Technische Universita"t Berlin
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Any use of this software is permitted provided that this notice is not
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removed and that neither the authors nor the Technische Universita"t
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Berlin are deemed to have made any representations as to the
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suitability of this software for any purpose nor are held responsible
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for any defects of this software. THERE IS ABSOLUTELY NO WARRANTY FOR
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THIS SOFTWARE.
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As a matter of courtesy, the authors request to be informed about uses
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this software has found, about bugs in this software, and about any
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improvements that may be of general interest.
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Berlin, 28.11.1994
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Jutta Degener
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Carsten Bormann
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*********************************************************************/
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#include <stdlib.h>
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#include <string.h>
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#include <math.h>
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#include "os.h"
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#include "smallft.h"
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#include "lpc.h"
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#include "scales.h"
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#include "misc.h"
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/* Autocorrelation LPC coeff generation algorithm invented by
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N. Levinson in 1947, modified by J. Durbin in 1959. */
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/* Input : n elements of time doamin data
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Output: m lpc coefficients, excitation energy */
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float vorbis_lpc_from_data(float *data,float *lpci,int n,int m){
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double *aut=alloca(sizeof(*aut)*(m+1));
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double *lpc=alloca(sizeof(*lpc)*(m));
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double error;
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double epsilon;
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int i,j;
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/* autocorrelation, p+1 lag coefficients */
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j=m+1;
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while(j--){
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double d=0; /* double needed for accumulator depth */
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for(i=j;i<n;i++)d+=(double)data[i]*data[i-j];
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aut[j]=d;
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}
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/* Generate lpc coefficients from autocorr values */
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/* set our noise floor to about -100dB */
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error=aut[0] * (1. + 1e-10);
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epsilon=1e-9*aut[0]+1e-10;
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for(i=0;i<m;i++){
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double r= -aut[i+1];
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if(error<epsilon){
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memset(lpc+i,0,(m-i)*sizeof(*lpc));
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goto done;
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}
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/* Sum up this iteration's reflection coefficient; note that in
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Vorbis we don't save it. If anyone wants to recycle this code
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and needs reflection coefficients, save the results of 'r' from
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each iteration. */
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for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];
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r/=error;
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/* Update LPC coefficients and total error */
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lpc[i]=r;
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for(j=0;j<i/2;j++){
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double tmp=lpc[j];
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lpc[j]+=r*lpc[i-1-j];
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lpc[i-1-j]+=r*tmp;
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}
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if(i&1)lpc[j]+=lpc[j]*r;
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error*=1.-r*r;
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}
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done:
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/* slightly damp the filter */
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{
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double g = .99;
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double damp = g;
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for(j=0;j<m;j++){
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lpc[j]*=damp;
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damp*=g;
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}
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}
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for(j=0;j<m;j++)lpci[j]=(float)lpc[j];
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/* we need the error value to know how big an impulse to hit the
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filter with later */
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return error;
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}
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void vorbis_lpc_predict(float *coeff,float *prime,int m,
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float *data,long n){
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/* in: coeff[0...m-1] LPC coefficients
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prime[0...m-1] initial values (allocated size of n+m-1)
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out: data[0...n-1] data samples */
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long i,j,o,p;
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float y;
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float *work=alloca(sizeof(*work)*(m+n));
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if(!prime)
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for(i=0;i<m;i++)
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work[i]=0.f;
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else
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for(i=0;i<m;i++)
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work[i]=prime[i];
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for(i=0;i<n;i++){
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y=0;
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o=i;
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p=m;
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for(j=0;j<m;j++)
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y-=work[o++]*coeff[--p];
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data[i]=work[o]=y;
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}
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}
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