Add basic windowed-sinc audio filters.

[dcpomatic.git] / src / lib / audio_filter.h

diff --git a/src/lib/audio_filter.h b/src/lib/audio_filter.h
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+/*
+    Copyright (C) 2014 Carl Hetherington <cth@carlh.net>
+
+    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; either version 2 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 for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#include <vector>
+#include <boost/shared_ptr.hpp>
+
+class AudioBuffers;
+class audio_filter_impulse_kernel_test;
+class audio_filter_impulse_input_test;
+
+class AudioFilter
+{
+public:
+       AudioFilter (float transition_bandwidth)
+       {
+               _M = 4 / transition_bandwidth;
+               if (_M % 2) {
+                       ++_M;
+               }
+       }
+
+       boost::shared_ptr<AudioBuffers> run (boost::shared_ptr<AudioBuffers> in);
+
+protected:
+       friend class audio_filter_impulse_kernel_test;
+       friend class audio_filter_impulse_input_test;
+
+       std::vector<float> sinc_blackman (float cutoff, bool invert) const;
+
+       std::vector<float> _ir;
+       int _M;
+       boost::shared_ptr<AudioBuffers> _tail;
+};
+
+class LowPassAudioFilter : public AudioFilter
+{
+public:
+       /** Construct a windowed-sinc low-pass filter using the Blackman window.
+        *  @param transition_bandwidth Transition bandwidth as a fraction of the sampling rate.
+        *  @param cutoff Cutoff frequency as a fraction of the sampling rate.
+        */
+       LowPassAudioFilter (float transition_bandwidth, float cutoff);
+};
+
+class HighPassAudioFilter : public AudioFilter
+{
+public:
+       /** Construct a windowed-sinc high-pass filter using the Blackman window.
+        *  @param transition_bandwidth Transition bandwidth as a fraction of the sampling rate.
+        *  @param cutoff Cutoff frequency as a fraction of the sampling rate.
+        */
+       HighPassAudioFilter (float transition_bandwidth, float cutoff);
+};
+
+class BandPassAudioFilter : public AudioFilter
+{
+public:
+       /** Construct a windowed-sinc band-pass filter using the Blackman window.
+        *  @param transition_bandwidth Transition bandwidth as a fraction of the sampling rate.
+        *  @param lower Lower cutoff frequency as a fraction of the sampling rate.
+        *  @param higher Higher cutoff frequency as a fraction of the sampling rate.
+        */
+       BandPassAudioFilter (float transition_bandwidth, float lower, float higher);
+};