cepstral

Digital Signal Processing Library

Voice Lab

cepstral

void cepstral(double lpc[], double cep[], int order)
{
 int n, k;
 double sumation, ratio;

 if(order >= MAX_ALLOC_SIZE) {
  fprintf(stderr, "Please increase MAX_ALLOC_SIZE in window_lib.h to at least %d\n", order+1);
  exit(1);
 }

 /* Information taken from Douglas O'Shaughnessy's book */
 /*  "Speech Communication, Human and Machine" 1990, page 356  equation 8.39 */
 /* lpc[0] = 1.0, coming from lpc routine */
 /* computed values stored from lpc[1] thru lpc[order] */

 /* copy the 1.0 at lpc[0] */
 cep[0] = lpc[0];

 /* equation 8.39 page 356 */
 for(n = 1; n <= order; n++) {
  sumation = 0.0;
  for(k = 1; k < n; k++) {
   ratio = (double)(k)/(double)(n);
   sumation += ratio*cep[k]*lpc[n-k];
  }
  cep[n] = lpc[n] + sumation;
 }
} /* End of the Cepstra function */