Fix and refactor fir filter

2026-07-08 20:33:13 -04:00 · 2020-10-31 21:30:45 +01:00
parent b9adbfb1d8
commit d7f8208814
17 changed files with 217 additions and 387 deletions
@@ -0,0 +1,52 @@
+///////////////////////////////////////////////////////////////////////////////////
+// Copyright (C) 2020 kasper93                                                   //
+// written by Kacper Michajłow and Edouard Griffiths                             //
+//                                                                               //
+// 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"
+
+void FirFilterGenerators::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);
+    }
+}