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Diffstat (limited to 'media/libvorbis/lib/vorbis_lpc.c')
| -rw-r--r-- | media/libvorbis/lib/vorbis_lpc.c | 160 |
1 files changed, 160 insertions, 0 deletions
diff --git a/media/libvorbis/lib/vorbis_lpc.c b/media/libvorbis/lib/vorbis_lpc.c new file mode 100644 index 000000000..f5199ec23 --- /dev/null +++ b/media/libvorbis/lib/vorbis_lpc.c @@ -0,0 +1,160 @@ +/******************************************************************** + * * + * THIS FILE IS PART OF THE OggVorbis SOFTWARE CODEC SOURCE CODE. * + * USE, DISTRIBUTION AND REPRODUCTION OF THIS LIBRARY SOURCE IS * + * GOVERNED BY A BSD-STYLE SOURCE LICENSE INCLUDED WITH THIS SOURCE * + * IN 'COPYING'. PLEASE READ THESE TERMS BEFORE DISTRIBUTING. * + * * + * THE OggVorbis SOURCE CODE IS (C) COPYRIGHT 1994-2009 * + * by the Xiph.Org Foundation http://www.xiph.org/ * + * * + ******************************************************************** + + function: LPC low level routines + last mod: $Id: lpc.c 16227 2009-07-08 06:58:46Z xiphmont $ + + ********************************************************************/ + +/* Some of these routines (autocorrelator, LPC coefficient estimator) + are derived from code written by Jutta Degener and Carsten Bormann; + thus we include their copyright below. The entirety of this file + is freely redistributable on the condition that both of these + copyright notices are preserved without modification. */ + +/* Preserved Copyright: *********************************************/ + +/* Copyright 1992, 1993, 1994 by Jutta Degener and Carsten Bormann, +Technische Universita"t Berlin + +Any use of this software is permitted provided that this notice is not +removed and that neither the authors nor the Technische Universita"t +Berlin are deemed to have made any representations as to the +suitability of this software for any purpose nor are held responsible +for any defects of this software. THERE IS ABSOLUTELY NO WARRANTY FOR +THIS SOFTWARE. + +As a matter of courtesy, the authors request to be informed about uses +this software has found, about bugs in this software, and about any +improvements that may be of general interest. + +Berlin, 28.11.1994 +Jutta Degener +Carsten Bormann + +*********************************************************************/ + +#include <stdlib.h> +#include <string.h> +#include <math.h> +#include "os.h" +#include "smallft.h" +#include "lpc.h" +#include "scales.h" +#include "misc.h" + +/* Autocorrelation LPC coeff generation algorithm invented by + N. Levinson in 1947, modified by J. Durbin in 1959. */ + +/* Input : n elements of time doamin data + Output: m lpc coefficients, excitation energy */ + +float vorbis_lpc_from_data(float *data,float *lpci,int n,int m){ + double *aut=alloca(sizeof(*aut)*(m+1)); + double *lpc=alloca(sizeof(*lpc)*(m)); + double error; + double epsilon; + int i,j; + + /* autocorrelation, p+1 lag coefficients */ + j=m+1; + while(j--){ + double d=0; /* double needed for accumulator depth */ + for(i=j;i<n;i++)d+=(double)data[i]*data[i-j]; + aut[j]=d; + } + + /* Generate lpc coefficients from autocorr values */ + + /* set our noise floor to about -100dB */ + error=aut[0] * (1. + 1e-10); + epsilon=1e-9*aut[0]+1e-10; + + for(i=0;i<m;i++){ + double r= -aut[i+1]; + + if(error<epsilon){ + memset(lpc+i,0,(m-i)*sizeof(*lpc)); + goto done; + } + + /* Sum up this iteration's reflection coefficient; note that in + Vorbis we don't save it. If anyone wants to recycle this code + and needs reflection coefficients, save the results of 'r' from + each iteration. */ + + for(j=0;j<i;j++)r-=lpc[j]*aut[i-j]; + r/=error; + + /* Update LPC coefficients and total error */ + + lpc[i]=r; + for(j=0;j<i/2;j++){ + double tmp=lpc[j]; + + lpc[j]+=r*lpc[i-1-j]; + lpc[i-1-j]+=r*tmp; + } + if(i&1)lpc[j]+=lpc[j]*r; + + error*=1.-r*r; + + } + + done: + + /* slightly damp the filter */ + { + double g = .99; + double damp = g; + for(j=0;j<m;j++){ + lpc[j]*=damp; + damp*=g; + } + } + + for(j=0;j<m;j++)lpci[j]=(float)lpc[j]; + + /* we need the error value to know how big an impulse to hit the + filter with later */ + + return error; +} + +void vorbis_lpc_predict(float *coeff,float *prime,int m, + float *data,long n){ + + /* in: coeff[0...m-1] LPC coefficients + prime[0...m-1] initial values (allocated size of n+m-1) + out: data[0...n-1] data samples */ + + long i,j,o,p; + float y; + float *work=alloca(sizeof(*work)*(m+n)); + + if(!prime) + for(i=0;i<m;i++) + work[i]=0.f; + else + for(i=0;i<m;i++) + work[i]=prime[i]; + + for(i=0;i<n;i++){ + y=0; + o=i; + p=m; + for(j=0;j<m;j++) + y-=work[o++]*coeff[--p]; + + data[i]=work[o]=y; + } +} |