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