/*
* Compute weights for a log point spaces critical band filter.
*
* @param window is the length of FFT to compute relative frequency.
* @param points is the length of filter kernel.
*/
void
cbweights(double *filter, int window, int points)
{
int i, center;
double step, w;
center = points/2;
step = pow((double)window, 1.0/(window-1.0));
filter[center] = butter(1.0);
w = 1;
for (i = 1; i <= points/2; i++) {
w *= step;
/* w = pow(step, (double)i); */
filter[center+i] = filter[center-i] = butter(w);
}
}
// makes the butterworth mask for a shifted dft by multiplying the coefficient to the dst
void butterFilter(cv::Mat_<float> &dst, int u, int v, float D0, int n){
int p = dst.rows;
int q = dst.cols;
for(int row = 0; row < p; row++){
for(int col = 0; col < q; col++){
dst.at<float>(row, col) = dst.at<float>(row, col) * butter(row - u, col + v, D0, n, p, q) * butter(row + u, col - v, D0, n, p, q);
}
}
}
int
main()
{
int offset;
double wr, mag, step;
step = pow(N, 1.0/(N-1));
for (offset = -15; offset <= 15; offset++) {
wr = pow(step, (double)offset);
mag = butter(wr);
printf("%4d: %f, %f, %f\n", offset, wr, mag, 20.0*log10(mag));
}
return 0;
}
