106 lines
2.6 KiB
C++
106 lines
2.6 KiB
C++
/*
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* Author: Harry van Haaren 2013
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* harryhaaren@gmail.com
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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, either 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 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 "dsp_sidechain_gain.hxx"
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// for pow()
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#include <cmath>
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SidechainGain::SidechainGain(int rate) :
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/// initial control values
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controlThreshold(0.2),
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controlReduction(1),
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controlReleaseTime(0.5),
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/// filter state init
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w(10.0f / (rate * 0.02)),
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a(0.07f),
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b(1.0f / (1.0f - a)),
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g1(0.0f),
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g2(0.0f),
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peakFrameCounter(0),
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peakCountDuration( rate / 4 ),
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currentTarget(0)
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{
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}
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void SidechainGain::process(unsigned int n_samples, float** inputs, float** outputs)
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{
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/// audio inputs
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float* inL = inputs[0];
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float* inR = inputs[1];
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float* side = inputs[2];
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float* outL = outputs[0];
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float* outR = outputs[1];
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/// control inputs
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float threshold = controlThreshold;
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float reduction = controlReduction;
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float releaseTime = controlReleaseTime;
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/// analyse sidechain input for peak
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float sum = 0.f;
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for( unsigned int i = 0; i < n_samples; i++ )
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{
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if ( *side > 0.000001 )
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sum += *side++;
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else
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sum += -*side++;
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}
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currentTarget = 0.f;
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/// check for peak level (offset to avoid "always on" peak)
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if ( sum / n_samples > threshold + 0.05 )
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{
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peakFrameCounter = peakCountDuration * releaseTime;
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currentTarget = 1.f - reduction;
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}
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else if ( peakFrameCounter < 0 )
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{
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currentTarget = 1.f;
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}
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else
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{
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currentTarget = 1.f - reduction;
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}
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if ( currentTarget < 0.f )
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currentTarget = 0.f;
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peakFrameCounter -= n_samples;
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for( unsigned int i = 0; i < n_samples; i++ )
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{
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/// smoothing algo is a lowpass, to de-zip the fades
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/// x^^4 approximates linear volume increase for human ears
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g1 += w * ( pow ( currentTarget, 4.f ) - g1 - a * g2 - 1e-20f);
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g2 += w * (b * g1 - g2 + 1e-20f);
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float gain = g2;
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*outL++ = *inL++ * gain;
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*outR++ = *inR++ * gain;
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}
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/// update output value
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controlSidechainAmp = currentTarget;
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}
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