/*
Analog formant filter response :
H(f) = i f B / (f1^2 - f^2 + i f B)
*/
static int Sound_into_FormantFilter_frame (Sound me, FormantFilter thee, long frame, double bw) {
Melder_assert (bw > 0);
autoMatrix pv = Sound_to_spectralpower (me);
double z1 = pv -> x1;
double dz = pv -> dx;
long nf = pv -> nx;
for (long i = 1; i <= thy ny; i++) {
double p = 0;
double fc = thy y1 + (i - 1) * thy dy;
double *pow = pv -> z[1];
for (long j = 1; j <= nf; j++) {
// H(f) = ifB / (fc^2 - f^2 + ifB)
// H(f)| = fB / sqrt ((fc^2 - f^2)^2 + f^2B^2)
//|H(f)|^2 = f^2B^2 / ((fc^2 - f^2)^2 + f^2B^2)
// = 1 / (((fc^2 - f^2) /fB)^2 + 1)
double f = z1 + (j - 1) * dz;
double a = NUMformantfilter_amplitude (fc, bw, f);
p += a * pow[j];
}
thy z[i][frame] = p;
}
return 1;
}
static int Sound_into_BarkFilter_frame (Sound me, BarkFilter thee, long frame) {
autoMatrix pv = Sound_to_spectralpower (me);
long nf = pv -> nx;
autoNUMvector<double> z (1, nf);
for (long j = 1; j <= nf; j++) {
z[j] = HZTOBARK (pv -> x1 + (j - 1) * pv -> dx);
}
for (long i = 1; i <= thy ny; i++) {
double p = 0;
double z0 = thy y1 + (i - 1) * thy dy;
double *pow = pv -> z[1]; // TODO ??
for (long j = 1; j <= nf; j++) {
// Sekey & Hanson filter is defined in the power domain.
// We therefore multiply the power with a (and not a^2).
// integral (F(z),z=0..25) = 1.58/9
double a = NUMsekeyhansonfilter_amplitude (z0, z[j]);
p += a * pow[j] ;
}
thy z[i][frame] = p;
}
return 1;
}
static int Sound_into_MelFilter_frame (Sound me, MelFilter thee, long frame) {
autoMatrix pv = Sound_to_spectralpower (me);
double z1 = pv -> x1;
double dz = pv -> dx;
long nf = pv -> nx;
double df = thy dy;
for (long i = 1; i <= thy ny; i++) {
double p = 0;
double fc_mel = thy y1 + (i - 1) * df;
double fc_hz = MELTOHZ (fc_mel);
double fl_hz = MELTOHZ (fc_mel - df);
double fh_hz = MELTOHZ (fc_mel + df);
double *pow = pv -> z[1];
for (long j = 1; j <= nf; j++) {
// Filter with a triangular filter the power (=amplitude-squared)
double f = z1 + (j - 1) * dz;
double a = NUMtriangularfilter_amplitude (fl_hz, fc_hz, fh_hz, f);
p += a * pow[j] ;
}
thy z[i][frame] = p;
}
return 1;
}
