mirror of https://github.com/f4exb/sdrangel.git
73 lines
2.6 KiB
C++
73 lines
2.6 KiB
C++
///////////////////////////////////////////////////////////////////////////////////
|
|
// Copyright (C) 2012 maintech GmbH, Otto-Hahn-Str. 15, 97204 Hoechberg, Germany //
|
|
// written by Christian Daniel //
|
|
// Copyright (C) 2015-2017, 2019-2020 Edouard Griffiths, F4EXB <f4exb06@gmail.com> //
|
|
// Copyright (C) 2020 Kacper Michajłow <kasper93@gmail.com> //
|
|
// //
|
|
// This program is free software; you can redistribute it and/or modify //
|
|
// it under the terms of the GNU General Public License as published by //
|
|
// the Free Software Foundation as version 3 of the License, or //
|
|
// (at your option) any later version. //
|
|
// //
|
|
// This program is distributed in the hope that it will be useful, //
|
|
// but WITHOUT ANY WARRANTY; without even the implied warranty of //
|
|
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the //
|
|
// GNU General Public License V3 for more details. //
|
|
// //
|
|
// You should have received a copy of the GNU General Public License //
|
|
// along with this program. If not, see <http://www.gnu.org/licenses/>. //
|
|
///////////////////////////////////////////////////////////////////////////////////
|
|
|
|
#include "firfilter.h"
|
|
|
|
namespace FirFilterGenerators
|
|
{
|
|
|
|
void generateLowPassFilter(int nTaps, double sampleRate, double cutoff, std::vector<Real> &taps)
|
|
{
|
|
if (!(nTaps & 1))
|
|
{
|
|
qDebug("Filter has to have an odd number of taps");
|
|
nTaps++;
|
|
}
|
|
|
|
double Wc = (2.0 * M_PI * cutoff) / sampleRate;
|
|
int halfTaps = nTaps / 2 + 1;
|
|
taps.resize(halfTaps);
|
|
|
|
for (int i = 0; i < halfTaps; ++i)
|
|
{
|
|
if (i == halfTaps - 1)
|
|
{
|
|
taps[i] = Wc / M_PI;
|
|
}
|
|
else
|
|
{
|
|
int n = i - (nTaps - 1) / 2;
|
|
taps[i] = sin(n * Wc) / (n * M_PI);
|
|
}
|
|
}
|
|
|
|
// Blackman window
|
|
for (int i = 0; i < halfTaps; i++)
|
|
{
|
|
int n = i - (nTaps - 1) / 2;
|
|
taps[i] *= 0.42 + 0.5 * cos((2.0 * M_PI * n) / nTaps) + 0.08 * cos((4.0 * M_PI * n) / nTaps);
|
|
}
|
|
|
|
Real sum = 0;
|
|
size_t i;
|
|
|
|
for (i = 0; i < taps.size() - 1; ++i) {
|
|
sum += taps[i] * 2.0;
|
|
}
|
|
|
|
sum += taps[i];
|
|
|
|
for (i = 0; i < taps.size(); ++i) {
|
|
taps[i] /= sum;
|
|
}
|
|
}
|
|
|
|
}
|