mirror of https://github.com/f4exb/sdrangel.git
149 lines
3.4 KiB
C++
149 lines
3.4 KiB
C++
// This file is part of LeanSDR Copyright (C) 2016-2018 <pabr@pabr.org>.
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// See the toplevel README for more information.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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#ifndef LEANSDR_FILTERGEN_H
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#define LEANSDR_FILTERGEN_H
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#include <math.h>
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#include "framework.h"
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namespace leansdr
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{
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namespace filtergen
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{
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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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{
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float s2 = 0;
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for (int i = 0; i < n; ++i) {
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s2 = s2 + coeffs[i] * coeffs[i]; // TBD complex
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}
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if (s2) {
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gain /= gen_sqrt(s2);
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}
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for (int i = 0; i < n; ++i) {
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coeffs[i] = coeffs[i] * gain;
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}
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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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{
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float s = 0;
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for (int i = 0; i < n; ++i) {
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s = s + coeffs[i];
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}
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if (s) {
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gain /= s;
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}
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for (int i = 0; i < n; ++i) {
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coeffs[i] = coeffs[i] * gain;
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}
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}
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template <typename T>
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void cancel_dcgain(int n, T *coeffs)
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{
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float s = 0;
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for (int i = 0; i < n; ++i) {
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s = s + coeffs[i];
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}
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for (int i = 0; i < n; ++i) {
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coeffs[i] -= s / n;
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}
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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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{
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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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{
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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, float gain=1)
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{
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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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{
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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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{
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c = (1 - B + 4*B/pi);
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}
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else
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{
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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/sqrtf(2) * ( (1+2/pi)*sinf(pi/(4*B)) + (1-2/pi)*cosf(pi/(4*B)) );
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} else {
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c = ( sinf(pi*tT*(1-B)) + 4*B*tT*cosf(pi*tT*(1+B)) ) / den;
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}
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}
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(*coeffs)[i] = Fs * c * gain;
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}
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return ncoeffs;
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}
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// Dump filter coefficients for matlab/octave
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void dump_filter(const char *name, int ncoeffs, float *coeffs);
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} // namespace filtergen
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} // namespace leansdr
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#endif // LEANSDR_FILTERGEN_H
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