void lpc(size_t lpc_ord, double lpc_stabl, size_t wsize, short *data, double *lpca,
double *ar, double *lpck, double *normerr, double *rms, double preemp,
window_type_t type)
{
double *dwind;
double rho[MAXORDER+1], k[MAXORDER], a[MAXORDER+1],*r,*kp,*ap,en,er;
double wfact = 1.0;
dwind = malloc(wsize*sizeof(double));
w_window(data, dwind, wsize, preemp, type);
if(!(r = ar)) r = rho;
if(!(kp = lpck)) kp = k;
if(!(ap = lpca)) ap = a;
autoc( wsize, dwind, lpc_ord, r, &en );
if(lpc_stabl > 1.0) { /* add a little to the diagonal for stability */
size_t i;
double ffact;
ffact =1.0/(1.0 + exp((-lpc_stabl/20.0) * log(10.0)));
for(i=1; i <= lpc_ord; i++) rho[i] = ffact * r[i];
*rho = *r;
r = rho;
if(ar)
for(i=0;i<=lpc_ord; i++) ar[i] = r[i]; /* copy out for possible use later */
}
durbin ( r, kp, &ap[1], lpc_ord, &er);
*ap = 1.0;
if(rms) *rms = en/wfact;
if(normerr) *normerr = er;
free(dwind);
}
void autohf(float *si, float *w, int n, float omega, float *a)
{
int i;
float c0, c[MAXNO], atemp[MAXNO+1], s[MAXLL];
memset(atemp, 0, sizeof(atemp));
for (i = 0; i < n ; i++)
s[i] = si[i] * w[i]; /* apply window */
cor(s, n, &c0, c); /* calculate autocorrelations */
atemp[0] = 1.0f; /* convert autocorrelations to pc's */
durbin(c0, c, &atemp[1]);
bwexp1(omega, atemp, a, MAXNO); /* expand corrected pc's */
}