JUCE/modules/juce_dsp/widgets/juce_Limiter.cpp

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2020 - Raw Material Software Limited

   JUCE is an open source library subject to commercial or open-source
   licensing.

   By using JUCE, you agree to the terms of both the JUCE 6 End-User License
   Agreement and JUCE Privacy Policy (both effective as of the 16th June 2020).

   End User License Agreement: www.juce.com/juce-6-licence
   Privacy Policy: www.juce.com/juce-privacy-policy

   Or: You may also use this code under the terms of the GPL v3 (see
   www.gnu.org/licenses).

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{
namespace dsp
{

//==============================================================================
template <typename SampleType>
void Limiter<SampleType>::setThreshold (SampleType newThreshold)
{
    thresholddB = newThreshold;
    update();
}

template <typename SampleType>
void Limiter<SampleType>::setRelease (SampleType newRelease)
{
    releaseTime = newRelease;
    update();
}

//==============================================================================
template <typename SampleType>
void Limiter<SampleType>::prepare (const ProcessSpec& spec)
{
    jassert (spec.sampleRate > 0);
    jassert (spec.numChannels > 0);

    sampleRate = spec.sampleRate;

    firstStageCompressor.prepare (spec);
    secondStageCompressor.prepare (spec);

    update();
    reset();
}

template <typename SampleType>
void Limiter<SampleType>::reset()
{
    firstStageCompressor.reset();
    secondStageCompressor.reset();

    outputVolume.reset (sampleRate, 0.001);
}

//==============================================================================
template <typename SampleType>
void Limiter<SampleType>::update()
{
    firstStageCompressor.setThreshold ((SampleType) -10.0);
    firstStageCompressor.setRatio     ((SampleType) 4.0);
    firstStageCompressor.setAttack    ((SampleType) 2.0);
    firstStageCompressor.setRelease   ((SampleType) 200.0);

    secondStageCompressor.setThreshold (thresholddB);
    secondStageCompressor.setRatio     ((SampleType) 1000.0);
    secondStageCompressor.setAttack    ((SampleType) 0.001);
    secondStageCompressor.setRelease   (releaseTime);

    auto ratioInverse = (SampleType) (1.0 / 4.0);

    auto gain = (SampleType) std::pow (10.0, 10.0 * (1.0 - ratioInverse) / 40.0);
    gain *= Decibels::decibelsToGain (-thresholddB, (SampleType) -100.0);

    outputVolume.setTargetValue (gain);
}

//==============================================================================
template class Limiter<float>;
template class Limiter<double>;

} // namespace dsp
} // namespace juce