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71 lines
2.4 KiB
C++
71 lines
2.4 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
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// Copyright (C) 2020 kasper93 //
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// written by Kacper Michajłow and Edouard Griffiths //
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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 as 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 V3 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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///////////////////////////////////////////////////////////////////////////////////
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#include "firfilter.h"
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namespace FirFilterGenerators
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{
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void generateLowPassFilter(int nTaps, double sampleRate, double cutoff, std::vector<Real> &taps)
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{
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if (!(nTaps & 1))
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{
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qDebug("Filter has to have an odd number of taps");
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nTaps++;
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}
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double Wc = (2.0 * M_PI * cutoff) / sampleRate;
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int halfTaps = nTaps / 2 + 1;
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taps.resize(halfTaps);
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for (int i = 0; i < halfTaps; ++i)
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{
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if (i == halfTaps - 1)
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{
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taps[i] = Wc / M_PI;
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}
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else
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{
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int n = i - (nTaps - 1) / 2;
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taps[i] = sin(n * Wc) / (n * M_PI);
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}
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}
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// Blackman window
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for (int i = 0; i < halfTaps; i++)
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{
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int n = i - (nTaps - 1) / 2;
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taps[i] *= 0.42 + 0.5 * cos((2.0 * M_PI * n) / nTaps) + 0.08 * cos((4.0 * M_PI * n) / nTaps);
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}
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Real sum = 0;
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size_t i;
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for (i = 0; i < taps.size() - 1; ++i) {
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sum += taps[i] * 2.0;
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}
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sum += taps[i];
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for (i = 0; i < taps.size(); ++i) {
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taps[i] /= sum;
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}
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}
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}
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