/*
* ----------------------------------------------------------
* Transform from s to z domain using bilinear transform
* with prewarp.
*
* Arguments:
* For argument description look at bilinear()
*
* coef - pointer to array of floating point coefficients,
* corresponding to output of bilinear transofrm
* (z domain).
*
* Note: frequencies are in Hz.
* ----------------------------------------------------------
*/
void szxform(
double *a0, double *a1, double *a2, /* numerator coefficients */
double *b0, double *b1, double *b2, /* denominator coefficients */
double fc, /* Filter cutoff frequency */
double fs, /* sampling rate */
double *k, /* overall gain factor */
float *coef) /* pointer to 4 iir coefficients */
{
/* Calculate a1 and a2 and overwrite the original values */
prewarp(a0, a1, a2, fc, fs);
prewarp(b0, b1, b2, fc, fs);
bilinear(*a0, *a1, *a2, *b0, *b1, *b2, k, fs, coef);
}
// a0-a2: numerator coefficients
// b0-b2: denominator coefficients
// fc: Filter cutoff frequency
// fs: sampling rate
// k: overall gain factor
// coef: pointer to 4 iir coefficients
static void szxform(double *a0, double *a1, double *a2, double *b0, double *b1, double *b2, double fc, double fs, double *k, float *coef) {
// Calculate a1 and a2 and overwrite the original values
prewarp(a1, a2, fc, fs);
prewarp(b1, b2, fc, fs);
bilinear(*a0, *a1, *a2, *b0, *b1, *b2, k, fs, coef);
}
