GainReductionComputer.h

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/*
 This file is part of the SimpleCompressor project.
 https://github.com/DanielRudrich/SimpleCompressor
 Copyright (c) 2019 Daniel Rudrich
 
 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, version 3.
 
 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, see <http://www.gnu.org/licenses/>.
 */
 
#pragma once
 
#include <vector>
#include <limits>
#include <cmath>
#include <atomic>
 
namespace DanielRudrich {
class GainReductionComputer
{
public:
    GainReductionComputer();
    ~GainReductionComputer() {}
 
    static float getCharacteristicSample(float inputLevelInDecibels,
                                         float kneeInDecibels,
                                         float thresholdInDecibels, float ratio,
                                         float makeUpGainInDecibels);
 
    // ======================================================================
    void setAttackTime (const float attackTimeInSeconds);
 
    void setReleaseTime (const float releaseTimeInSeconds);
 
    void setKnee (const float kneeInDecibels);
    const float getKnee() { return knee; }
 
    void setThreshold (const float thresholdInDecibels);
    const float getThreshold() { return threshold; }
 
    void setMakeUpGain (const float makeUpGainInDecibels);
    const float getMakeUpGain()  { return makeUpGain; }
 
    void setRatio (const float ratio);
 
    // ======================================================================
    void getCharacteristic (float* inputLevelsInDecibels, float* destination, const int numSamples);
 
    float getCharacteristicSample (const float inputLevelInDecibels);
 
    // ======================================================================
    void prepare (const double sampleRate);
 
    void reset() { state = 0.0f; }
 
    void computeGainInDecibelsFromSidechainSignal (const float* sideChainSignal, float* destination, const int numSamples);
 
    void computeLinearGainFromSidechainSignal (const float* sideChainSignal, float* destination, const int numSamples);
 
    const float getMaxInputLevelInDecibels() { return maxInputLevel; }
    const float getMaxGainReductionInDecibels() { return maxGainReduction; }
 
private:
    static float applyCharacteristicToOverShoot(float overShootInDecibels,
                                                float knee, float slope);
 
    inline const float timeToGain (const float timeInSeconds);
    inline const float applyCharacteristicToOverShoot (const float overShootInDecibels);
 
    double sampleRate;
 
    // parameters
    float knee, kneeHalf;
    float threshold;
    float attackTime;
    float releaseTime;
    float slope;
    float makeUpGain;
 
    std::atomic<float> maxInputLevel {-std::numeric_limits<float>::infinity()};
    std::atomic<float> maxGainReduction {0};
 
    //state variable
    float state;
 
    float alphaAttack;
    float alphaRelease;
};
} // namespace DanielRudrich