std::vector<double> calculate_decimator_taps(unsigned int rate, int low_rate_multipliers, bool use_fir)
{
const size_t IIR_Order = low_rate_multipliers/2;
const double ripple = 0.1;
const size_t Order=(2*low_rate_multipliers*rate)+1;
const double fc = 0.5/rate;
const double pass_edge = 0.8*fc;
if (use_fir) {
const double remez_stop_atten = 60.0;
const double remez_trans = 2*(fc - pass_edge);
const double remez_weight = remez_estimate_weight(ripple, remez_stop_atten);
auto taps = design_fir("remez","LOW_PASS", (int)Order, pass_edge, 0, remez_trans, remez_weight);
return taps;
} else {
iir_coeff* filt = design_iir("chebyshev", "LOW_PASS", (int)IIR_Order, pass_edge, ripple);
// get the tap from iir_coeff for iir_filter, incorporating the gain to feedforward taps
std::vector<double> b = filt->get_b();
std::vector<double> a = filt->get_a();
// Group together feed forward and feed back taps into 1 vector for transferring to IIR filter
for (size_t i=0;i<a.size();i++) b.push_back(a[i]);
return b;
}
}
float* calc_coefficients_125Hz_lowpass(int rate)
{
len125 = 256;
float f = 125.0f / (rate / 2);
float *coeffs = design_fir(&len125, &f, 0);
static const float M3_01DB = 0.7071067812f;
for (unsigned int i = 0; i < len125; i++)
{
coeffs[i] *= M3_01DB;
}
return coeffs;
}
