Signal Processing Library

Program name: cepstra

Language: C

In file: parameter_lib.c

Objective: Calculate the Cepstal Coefficients from the LPC vector

Usage: void cepstral(double lpc[], double cep[], int order);

Parameters:

• lpc - The LPC vector for the window of input data
• cep - The output array to put the calculated data
• order - The order

• void

Mathematical Description:

Comments:

User Comments

Code:

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 cepstral function */