vx32

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lpc.c (4295B)

      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 1994-2002             *
      9  * by the XIPHOPHORUS Company http://www.xiph.org/                  *
     10  *                                                                  *
     11  ********************************************************************
     12 
     13   function: LPC low level routines
     14   last mod: $Id: lpc.c 1919 2005-07-24 14:18:04Z baford $
     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   int i,j;
     66 
     67   /* autocorrelation, p+1 lag coefficients */
     68   j=m+1;
     69   while(j--){
     70     double d=0; /* double needed for accumulator depth */
     71     for(i=j;i<n;i++)d+=(double)data[i]*data[i-j];
     72     aut[j]=d;
     73   }
     74   
     75   /* Generate lpc coefficients from autocorr values */
     76 
     77   error=aut[0];
     78   
     79   for(i=0;i<m;i++){
     80     double r= -aut[i+1];
     81 
     82     if(error==0){
     83       memset(lpci,0,m*sizeof(*lpci));
     84       return 0;
     85     }
     86 
     87     /* Sum up this iteration's reflection coefficient; note that in
     88        Vorbis we don't save it.  If anyone wants to recycle this code
     89        and needs reflection coefficients, save the results of 'r' from
     90        each iteration. */
     91 
     92     for(j=0;j<i;j++)r-=lpc[j]*aut[i-j];
     93     r/=error; 
     94 
     95     /* Update LPC coefficients and total error */
     96     
     97     lpc[i]=r;
     98     for(j=0;j<i/2;j++){
     99       double tmp=lpc[j];
    100 
    101       lpc[j]+=r*lpc[i-1-j];
    102       lpc[i-1-j]+=r*tmp;
    103     }
    104     if(i%2)lpc[j]+=lpc[j]*r;
    105 
    106     error*=1.f-r*r;
    107   }
    108 
    109   for(j=0;j<m;j++)lpci[j]=(float)lpc[j];
    110 
    111   /* we need the error value to know how big an impulse to hit the
    112      filter with later */
    113   
    114   return error;
    115 }
    116 
    117 void vorbis_lpc_predict(float *coeff,float *prime,int m,
    118                      float *data,long n){
    119 
    120   /* in: coeff[0...m-1] LPC coefficients 
    121          prime[0...m-1] initial values (allocated size of n+m-1)
    122     out: data[0...n-1] data samples */
    123 
    124   long i,j,o,p;
    125   float y;
    126   float *work=alloca(sizeof(*work)*(m+n));
    127 
    128   if(!prime)
    129     for(i=0;i<m;i++)
    130       work[i]=0.f;
    131   else
    132     for(i=0;i<m;i++)
    133       work[i]=prime[i];
    134 
    135   for(i=0;i<n;i++){
    136     y=0;
    137     o=i;
    138     p=m;
    139     for(j=0;j<m;j++)
    140       y-=work[o++]*coeff[--p];
    141     
    142     data[i]=work[o]=y;
    143   }
    144 }
    145 
    146 
    147 
    148 
    149