2 Copyright (C) 2014-2021 Carl Hetherington <cth@carlh.net>
4 This file is part of DCP-o-matic.
6 DCP-o-matic is free software; you can redistribute it and/or modify
7 it under the terms of the GNU General Public License as published by
8 the Free Software Foundation; either version 2 of the License, or
9 (at your option) any later version.
11 DCP-o-matic is distributed in the hope that it will be useful,
12 but WITHOUT ANY WARRANTY; without even the implied warranty of
13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 GNU General Public License for more details.
16 You should have received a copy of the GNU General Public License
17 along with DCP-o-matic. If not, see <http://www.gnu.org/licenses/>.
22 #include "audio_filter.h"
23 #include "audio_buffers.h"
24 #include "maths_util.h"
29 using std::make_shared;
31 using std::shared_ptr;
35 AudioFilter::sinc_blackman (float cutoff, bool invert) const
37 auto ir = std::vector<float>();
40 /* Impulse response */
42 for (int i = 0; i <= _M; ++i) {
44 ir[i] = 2 * M_PI * cutoff;
47 ir[i] = sin (2 * M_PI * cutoff * (i - _M / 2)) / (i - _M / 2);
49 ir[i] *= (0.42 - 0.5 * cos (2 * M_PI * i / _M) + 0.08 * cos (4 * M_PI * i / _M));
56 for (int i = 0; i <= _M; ++i) {
60 for (int i = 0; i <= _M; ++i) {
64 /* Frequency inversion (swapping low-pass for high-pass, or whatever) */
67 for (int i = 0; i <= _M; ++i) {
77 shared_ptr<AudioBuffers>
78 AudioFilter::run (shared_ptr<const AudioBuffers> in)
80 auto out = make_shared<AudioBuffers>(in->channels(), in->frames());
83 _tail = make_shared<AudioBuffers>(in->channels(), _M + 1);
84 _tail->make_silent ();
87 int const channels = in->channels ();
88 int const frames = in->frames ();
90 for (int i = 0; i < channels; ++i) {
91 auto tail_p = _tail->data (i);
92 auto in_p = in->data (i);
93 auto out_p = out->data (i);
94 for (int j = 0; j < frames; ++j) {
96 for (int k = 0; k <= _M; ++k) {
98 s += tail_p[j - k + _M + 1] * _ir[k];
100 s += in_p[j - k] * _ir[k];
108 int const amount = min (in->frames(), _tail->frames());
109 if (amount < _tail->frames ()) {
110 _tail->move (_tail->frames() - amount, amount, 0);
112 _tail->copy_from (in.get(), amount, in->frames() - amount, _tail->frames () - amount);
119 AudioFilter::flush ()
125 LowPassAudioFilter::LowPassAudioFilter (float transition_bandwidth, float cutoff)
126 : AudioFilter (transition_bandwidth)
128 _ir = sinc_blackman (cutoff, false);
132 HighPassAudioFilter::HighPassAudioFilter (float transition_bandwidth, float cutoff)
133 : AudioFilter (transition_bandwidth)
135 _ir = sinc_blackman (cutoff, true);
139 BandPassAudioFilter::BandPassAudioFilter (float transition_bandwidth, float lower, float higher)
140 : AudioFilter (transition_bandwidth)
142 auto lpf = sinc_blackman (lower, false);
143 auto hpf = sinc_blackman (higher, true);
145 _ir.reserve (_M + 1);
146 for (int i = 0; i <= _M; ++i) {
147 _ir[i] = lpf[i] + hpf[i];
150 /* We now have a band-stop, so invert for band-pass */
151 for (int i = 0; i <= _M; ++i) {