mirror of
https://github.com/f4exb/sdrangel.git
synced 2024-09-18 02:46:35 -04:00
91 lines
2.4 KiB
C
91 lines
2.4 KiB
C
|
#ifndef LEANSDR_FILTERGEN_H
|
||
|
#define LEANSDR_FILTERGEN_H
|
||
|
|
||
|
#include <math.h>
|
||
|
|
||
|
namespace leansdr {
|
||
|
namespace filtergen {
|
||
|
|
||
|
template<typename T>
|
||
|
void normalize_power(int n, T *coeffs, float gain=1) {
|
||
|
float s2 = 0;
|
||
|
for ( int i=0; i<n; ++i ) s2 = s2 + coeffs[i]*coeffs[i]; // TBD complex
|
||
|
if ( s2 ) gain /= gen_sqrt(s2);
|
||
|
for ( int i=0; i<n; ++i ) coeffs[i] = coeffs[i] * gain;
|
||
|
}
|
||
|
|
||
|
template<typename T>
|
||
|
void normalize_dcgain(int n, T *coeffs, float gain=1) {
|
||
|
float s = 0;
|
||
|
for ( int i=0; i<n; ++i ) s = s + coeffs[i];
|
||
|
if ( s ) gain /= s;
|
||
|
for ( int i=0; i<n; ++i ) coeffs[i] = coeffs[i] * gain;
|
||
|
}
|
||
|
|
||
|
// Generate coefficients for a sinc filter.
|
||
|
// https://en.wikipedia.org/wiki/Sinc_filter
|
||
|
|
||
|
template<typename T>
|
||
|
int lowpass(int order, float Fcut, T **coeffs, float gain=1) {
|
||
|
int ncoeffs = order + 1;
|
||
|
*coeffs = new T[ncoeffs];
|
||
|
for ( int i=0; i<ncoeffs; ++i ) {
|
||
|
float t = i - (ncoeffs-1)*0.5;
|
||
|
float sinc = 2*Fcut * (t ? sin(2*M_PI*Fcut*t)/(2*M_PI*Fcut*t) : 1);
|
||
|
#if 0 // Hamming
|
||
|
float alpha = 25.0/46, beta = 21.0/46;
|
||
|
float window = alpha - beta*cos(2*M_PI*i/order);
|
||
|
#else
|
||
|
float window = 1;
|
||
|
#endif
|
||
|
(*coeffs)[i] = sinc * window;
|
||
|
}
|
||
|
normalize_dcgain(ncoeffs, *coeffs, gain);
|
||
|
return ncoeffs;
|
||
|
}
|
||
|
|
||
|
|
||
|
// Generate coefficients for a RRC filter.
|
||
|
// https://en.wikipedia.org/wiki/Root-raised-cosine_filter
|
||
|
|
||
|
template<typename T>
|
||
|
int root_raised_cosine(int order, float Fs, float rolloff, T **coeffs) {
|
||
|
float B = rolloff, pi = M_PI;
|
||
|
int ncoeffs = (order+1) | 1;
|
||
|
*coeffs = new T[ncoeffs];
|
||
|
for ( int i=0; i<ncoeffs; ++i ) {
|
||
|
int t = i - ncoeffs/2;
|
||
|
float c;
|
||
|
if ( t == 0 )
|
||
|
c = sqrt(Fs) * (1-B+4*B/pi);
|
||
|
else {
|
||
|
float tT = t * Fs;
|
||
|
float den = pi*tT*(1-(4*B*tT)*(4*B*tT));
|
||
|
if ( ! den )
|
||
|
c = B*sqrt(Fs/2) * ( (1+2/pi)*sin(pi/(4*B)) +
|
||
|
(1-2/pi)*cos(pi/(4*B)) );
|
||
|
else
|
||
|
c = sqrt(Fs) * ( sin(pi*tT*(1-B)) +
|
||
|
4*B*tT*cos(pi*tT*(1+B)) ) / den;
|
||
|
}
|
||
|
(*coeffs)[i] = c;
|
||
|
}
|
||
|
normalize_dcgain(ncoeffs, *coeffs);
|
||
|
return ncoeffs;
|
||
|
}
|
||
|
|
||
|
|
||
|
// Dump filter coefficients for matlab/octave
|
||
|
|
||
|
inline void dump_filter(const char *name, int ncoeffs, float *coeffs) {
|
||
|
fprintf(stderr, "%s = [", name);
|
||
|
for ( int i=0; i<ncoeffs; ++i )
|
||
|
fprintf(stderr, "%s %f", (i?",":""), coeffs[i]);
|
||
|
fprintf(stderr, " ];\n");
|
||
|
}
|
||
|
|
||
|
} // namespace
|
||
|
} // namespace
|
||
|
|
||
|
#endif // LEANSDR_FILTERGEN_H
|