Signal Processing Library

Program name: autocorrelation

Language: C

In file: parameter_lib.c

Objective: Calculate the autocorrelation of the data in the window

Usage: void autocorrelation(double *d_window_i, double ac[], int window_size, int order, int options);

Parameters:

• d_window_i - The double window of input data
• ac - The output array to put the calculated data
• window_size - The length of the window
• order - The order
• options
  • 2 - divide each element by the first element
  • 4 - divide each element by max value
  • 8 - divide each element by number of elements in input vector

• void

Mathematical Description:

Comments: Routine to calculate the autocorrelation of the data in the window

User Comments

Code:

void autocorrelation(double *d_window_i, double **ac, int window_size, int order, int options)
{
        int i, n;
        double max, tmp;

        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 37 equation 2.56 */
        DEBUG_WRITE(1, "Calculating autocorrelation coefficients\n");
        /* Calculation of autocorrelation coefficients */

        /* One interesting fact is that there needs to be one more value than the order of the filter */
        /* Therefore, the array needs to be dimensioned for order+1 locations */

        /* Another interesting fact is that when i = 0 we have the sum of the squares */

        max = 0.0;
        for(i = 0; i <= order; i++) {
                (*ac)[i] = 0.0; /* Start with a value of zero */
                for(n = 0; n < (window_size-i); n++) {
                        /* then sum the rest of the values */
                        (*ac)[i] += d_window_i[n]*d_window_i[n+i];
                }
                if((*ac)[i] >= 0) {
                        /* value is positive or zero */
                        if(max < (*ac)[i]) max = (*ac)[i];
                } else {
                        /* value is negative -> change sign */
                        if(max < (-(*ac)[i])) max = (-(*ac)[i]);
                }
                DEBUG_WRITE2(1, "max: %f\n", max);
                DEBUG_WRITE3(1, "(*ac)[%d]: %f\n", i, (*ac)[i]);
        }

        tmp = (*ac)[0];
        if(options & 0x02) for(i = 0; i <= order; i++) (*ac)[i] /= tmp;
        if(options & 0x04) for(i = 0; i <= order; i++) (*ac)[i] /= max;
        if(options & 0x08) for(i = 0; i <= order; i++) (*ac)[i] /= window_size;
        return;
}