juce_LadderFilter.cpp

/*
  ==============================================================================
 
   This file is part of the JUCE library.
   Copyright (c) 2022 - 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 7 End-User License
   Agreement and JUCE Privacy Policy.
 
   End User License Agreement: www.juce.com/juce-7-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::dsp
{
 
//==============================================================================
template <typename SampleType>
LadderFilter<SampleType>::LadderFilter()  : state (2)
{
    setSampleRate (SampleType (1000));  // intentionally setting unrealistic default
                                        // sample rate to catch missing initialisation bugs
    setResonance (SampleType (0));
    setDrive     (SampleType (1.2));
 
    mode = Mode::LPF24;
    setMode (Mode::LPF12);
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::setMode (Mode newMode) noexcept
{
    if (newMode == mode)
        return;
 
    switch (newMode)
    {
        case Mode::LPF12:   A = {{ SampleType (0), SampleType (0),  SampleType (1), SampleType (0),  SampleType (0) }}; comp = SampleType (0.5);  break;
        case Mode::HPF12:   A = {{ SampleType (1), SampleType (-2), SampleType (1), SampleType (0),  SampleType (0) }}; comp = SampleType (0);    break;
        case Mode::BPF12:   A = {{ SampleType (0), SampleType (0), SampleType (-1), SampleType (1),  SampleType (0) }}; comp = SampleType (0.5);  break;
        case Mode::LPF24:   A = {{ SampleType (0), SampleType (0),  SampleType (0), SampleType (0),  SampleType (1) }}; comp = SampleType (0.5);  break;
        case Mode::HPF24:   A = {{ SampleType (1), SampleType (-4), SampleType (6), SampleType (-4), SampleType (1) }}; comp = SampleType (0);    break;
        case Mode::BPF24:   A = {{ SampleType (0), SampleType (0),  SampleType (1), SampleType (-2), SampleType (1) }}; comp = SampleType (0.5);  break;
        default:            jassertfalse;                                                                                                         break;
    }
 
    static constexpr auto outputGain = SampleType (1.2);
 
    for (auto& a : A)
        a *= outputGain;
 
    mode = newMode;
    reset();
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::prepare (const ProcessSpec& spec)
{
    setSampleRate (SampleType (spec.sampleRate));
    setNumChannels (spec.numChannels);
    reset();
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::reset() noexcept
{
    for (auto& s : state)
        s.fill (SampleType (0));
 
    cutoffTransformSmoother.setCurrentAndTargetValue (cutoffTransformSmoother.getTargetValue());
    scaledResonanceSmoother.setCurrentAndTargetValue (scaledResonanceSmoother.getTargetValue());
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::setCutoffFrequencyHz (SampleType newCutoff) noexcept
{
    jassert (newCutoff > SampleType (0));
    cutoffFreqHz = newCutoff;
    updateCutoffFreq();
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::setResonance (SampleType newResonance) noexcept
{
    jassert (newResonance >= SampleType (0) && newResonance <= SampleType (1));
    resonance = newResonance;
    updateResonance();
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::setDrive (SampleType newDrive) noexcept
{
    jassert (newDrive >= SampleType (1));
 
    drive = newDrive;
    gain = std::pow (drive, SampleType (-2.642))   * SampleType (0.6103) + SampleType (0.3903);
    drive2 = drive                                 * SampleType (0.04)   + SampleType (0.96);
    gain2 = std::pow (drive2, SampleType (-2.642)) * SampleType (0.6103) + SampleType (0.3903);
}
 
//==============================================================================
template <typename SampleType>
SampleType LadderFilter<SampleType>::processSample (SampleType inputValue, size_t channelToUse) noexcept
{
    auto& s = state[channelToUse];
 
    const auto a1 = cutoffTransformValue;
    const auto g = a1 * SampleType (-1) + SampleType (1);
    const auto b0 = g * SampleType (0.76923076923);
    const auto b1 = g * SampleType (0.23076923076);
 
    const auto dx = gain * saturationLUT (drive * inputValue);
    const auto a  = dx + scaledResonanceValue * SampleType (-4) * (gain2 * saturationLUT (drive2 * s[4]) - dx * comp);
 
    const auto b = b1 * s[0] + a1 * s[1] + b0 * a;
    const auto c = b1 * s[1] + a1 * s[2] + b0 * b;
    const auto d = b1 * s[2] + a1 * s[3] + b0 * c;
    const auto e = b1 * s[3] + a1 * s[4] + b0 * d;
 
    s[0] = a;
    s[1] = b;
    s[2] = c;
    s[3] = d;
    s[4] = e;
 
    return a * A[0] + b * A[1] + c * A[2] + d * A[3] + e * A[4];
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::updateSmoothers() noexcept
{
    cutoffTransformValue = cutoffTransformSmoother.getNextValue();
    scaledResonanceValue = scaledResonanceSmoother.getNextValue();
}
 
//==============================================================================
template <typename SampleType>
void LadderFilter<SampleType>::setSampleRate (SampleType newValue) noexcept
{
    jassert (newValue > SampleType (0));
    cutoffFreqScaler = SampleType (-2.0 * juce::MathConstants<double>::pi) / newValue;
 
    static constexpr SampleType smootherRampTimeSec = SampleType (0.05);
    cutoffTransformSmoother.reset (newValue, smootherRampTimeSec);
    scaledResonanceSmoother.reset (newValue, smootherRampTimeSec);
 
    updateCutoffFreq();
}
 
//==============================================================================
template class LadderFilter<float>;
template class LadderFilter<double>;
 
} // namespace juce::dsp