//! Band stop: sample rate, lower frequency, upper frequency, window
std::vector<double> sincBSF(const size_t numTaps, const double Fl, const double Fu)
{
std::vector<double> taps(numTaps);
const auto lambda = M_PI * Fl / (0.5);
const auto phi = M_PI * Fu / (0.5);
for (size_t n = 0; n < numTaps; n++)
{
const double mm = n - (numTaps - 1.0) / 2.0;
if( mm == 0.0 ) taps[n] = 1.0 - (phi - lambda) / M_PI;
else taps[n] = -( sin( mm * phi ) -
sin( mm * lambda ) ) / (mm * M_PI);
}
return taps;
}
static std::vector<Real> createPolyphaseLowPass(
int phaseSteps,
double gain,
double sampleRateHz,
double cutoffFreqHz,
double transitionWidthHz,
double oobAttenuationdB)
{
int ntaps = (int)(oobAttenuationdB * sampleRateHz / (22.0 * transitionWidthHz));
if((ntaps % 2) != 0)
ntaps++;
ntaps *= phaseSteps;
std::vector<float> taps(ntaps);
std::vector<float> window(ntaps);
for(int n = 0; n < ntaps; n++)
window[n] = 0.54 - 0.46 * cos ((2 * M_PI * n) / (ntaps - 1));
int M = (ntaps - 1) / 2;
double fwT0 = 2 * M_PI * cutoffFreqHz / sampleRateHz;
for(int n = -M; n <= M; n++) {
if(n == 0) taps[n + M] = fwT0 / M_PI * window[n + M];
else taps[n + M] = sin (n * fwT0) / (n * M_PI) * window[n + M];
}
double max = taps[0 + M];
for(int n = 1; n <= M; n++)
max += 2.0 * taps[n + M];
gain /= max;
for(int i = 0; i < ntaps; i++)
taps[i] *= gain;
return taps;
}