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/* lpc.c -- implement LPC analysis */
#include <math.h>
#ifndef mips
#include "stdlib.h"
#endif
#include "xlisp.h"
void abs_max(double *x, long desde, long hasta, double *x_maxptr, long *indptr)
{
/* use:
abs_max(s,0,10,&mimax,&miind);
*/
double x_max = x[desde];
long ind = desde;
long i;
for(i = desde+1; i<hasta; i++)
if (fabs(x[i]) > x_max)
{
x_max = fabs(x[i]);
ind = i;
}
*x_maxptr = x_max;
*indptr = ind;
}
void xcorr(double *s, double *rxx, long N)
{
/* use:
xcorr(s,rxx,N);
*/
long i,j;
for(i=0; i < N; i++)
{
rxx[i] = 0.0;
for(j=0; j < N-i; j++)
rxx[i] += s[j]*s[j+i];
}
}
// SOUND PARAMETERS
// w Lisp vector containinig signal values
// P number of poles
// N length of sound
// AUTOCORRELEATION PARAMETERS
// rxx array containing autocorrelation coefs
// max_rxx temporal maximun value of rxx
// i_max index of max_rxx
// LPC PARAMETERS
// alpha array of filter coefs
// k reflection coef
// E residual energy
// rms1 energy of input signal (not RMS)
// rms2 residual energy = E
// unv voiced/unvoiced parameter = ERR = rms2/rms1
// PITCH DETECTION ALGORITHM: Implemented separately
LVAL snd_lpanal(LVAL w, long P)
{
double *s, *rxx;
long N;
double *alpha;
// double *k, *E; THIS ONLY FOR VECTORIZED k AND E
double k, E;
double rms1; // rms2=E;
double unv;
double suma, alphatemp; // help variables
long i,j;
LVAL result;
xlsave1(result);
//// end vars /////////////
//// allocate memory ///////
N = getsize(w);
s = calloc(sizeof(double),N); //signal
rxx = calloc(sizeof(double),N); //autocorrelation
alpha = calloc(sizeof(double), P); // filter coefs
//k = calloc(sizeof(double), P); // reflection coefs
//E = calloc(sizeof(double), P); // residual energy
////// copy Lisp array sound data to array of double ///////
for(i=0; i<N; i++)
s[i] = getflonum(getelement(w,i));
///// autocorrelation ////////////////
xcorr(s,rxx,N); // this may be optimized as only P autocorr factors are needed (not N)
//////// LPC analysis //////////////////////////////////
/// Durbin algorithm
/// inicialization
//for(i=0; i<P;i++)
// alpha[i]=k[i]=E[i]=0.0; // don't need this. Done by default.
//E[0] = rxx[0] - pow(rxx[1],2)/rxx[0];
//k[0] = rxx[1]/rxx[0];
//alpha[0] = k[0];
E = rxx[0] - pow(rxx[1],2)/rxx[0]; // NO VECTORS k OR E
k = rxx[1]/rxx[0]; //
alpha[0] = k; //
/// recursive solve
for(i=1;i<P;i++)
{
suma=0.0;
for(j=0;j<i;j++)
suma += alpha[j] * rxx[i-j];
//k[i] = (rxx[i+1]-suma)/E[i-1];
//alpha[i]=k[i];
k = (rxx[i+1]-suma)/E;
alpha[i]=k;
for(j=0; j <= ((i-1) >> 1); j++)
{
//alphatemp = alpha[j] - k[i] * alpha[i-j-1];
//alpha[i-j-1] -= k[i] * alpha[j];
//alpha[j] = alphatemp;
alphatemp = alpha[j] - k * alpha[i-j-1];
alpha[i-j-1] -= k * alpha[j];
alpha[j] = alphatemp;
}
//E[i] = E[i-1] * (1 - pow(k[i],2));
E *= (1 - pow(k,2));
}
// input signal energy = rxx[0];
rms1 = rxx[0];
// voiced/unvoiced
unv= sqrt(E/rms1);
///// HERE: CHECK STABILITY AND MODIFY COEFS /////////////
///// not implemented
// prepare output result
result = newvector(P);
for (i = 0; i < P; i++) setelement(result, i, cvflonum(alpha[P-i-1])); // alpoles format
xlpop();
// free memory
free(s); free(rxx); free(alpha);
return (cons (cvflonum(rms1), // input signal energy
cons(cvflonum(E), // residual energy
cons(cvflonum(unv), // ERR, voiced/unvoiced
cons(result, NULL))))); // coefs
}
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