juce_LadderFilter.h

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 /*
  ==============================================================================
 
   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
{
 
enum class LadderFilterMode
{
    LPF12,  // low-pass  12 dB/octave
    HPF12,  // high-pass 12 dB/octave
    BPF12,  // band-pass 12 dB/octave
    LPF24,  // low-pass  24 dB/octave
    HPF24,  // high-pass 24 dB/octave
    BPF24   // band-pass 24 dB/octave
};
 
template <typename SampleType>
class LadderFilter
{
public:
    //==============================================================================
    using Mode = LadderFilterMode;
 
    //==============================================================================
    LadderFilter();
 
    void setEnabled (bool isEnabled) noexcept    { enabled = isEnabled; }
 
    void setMode (Mode newMode) noexcept;
 
    void prepare (const ProcessSpec& spec);
 
    size_t getNumChannels() const noexcept       { return state.size(); }
 
    void reset() noexcept;
 
    void setCutoffFrequencyHz (SampleType newCutoff) noexcept;
 
    void setResonance (SampleType newResonance) noexcept;
 
    void setDrive (SampleType newDrive) noexcept;
 
    //==============================================================================
    template <typename ProcessContext>
    void process (const ProcessContext& context) noexcept
    {
        const auto& inputBlock = context.getInputBlock();
        auto& outputBlock      = context.getOutputBlock();
        const auto numChannels = outputBlock.getNumChannels();
        const auto numSamples  = outputBlock.getNumSamples();
 
        jassert (inputBlock.getNumChannels() <= getNumChannels());
        jassert (inputBlock.getNumChannels() == numChannels);
        jassert (inputBlock.getNumSamples()  == numSamples);
 
        if (! enabled || context.isBypassed)
        {
            outputBlock.copyFrom (inputBlock);
            return;
        }
 
        for (size_t n = 0; n < numSamples; ++n)
        {
            updateSmoothers();
 
            for (size_t ch = 0; ch < numChannels; ++ch)
                outputBlock.getChannelPointer (ch)[n] = processSample (inputBlock.getChannelPointer (ch)[n], ch);
        }
    }
 
protected:
    //==============================================================================
    SampleType processSample (SampleType inputValue, size_t channelToUse) noexcept;
    void updateSmoothers() noexcept;
 
private:
    //==============================================================================
    void setSampleRate (SampleType newValue) noexcept;
    void setNumChannels (size_t newValue)   { state.resize (newValue); }
    void updateCutoffFreq() noexcept        { cutoffTransformSmoother.setTargetValue (std::exp (cutoffFreqHz * cutoffFreqScaler)); }
    void updateResonance() noexcept         { scaledResonanceSmoother.setTargetValue (jmap (resonance, SampleType (0.1), SampleType (1.0))); }
 
    //==============================================================================
    SampleType drive, drive2, gain, gain2, comp;
 
    static constexpr size_t numStates = 5;
    std::vector<std::array<SampleType, numStates>> state;
    std::array<SampleType, numStates> A;
 
    SmoothedValue<SampleType> cutoffTransformSmoother, scaledResonanceSmoother;
    SampleType cutoffTransformValue, scaledResonanceValue;
 
    LookupTableTransform<SampleType> saturationLUT { [] (SampleType x) { return std::tanh (x); },
                                                     SampleType (-5), SampleType (5), 128 };
 
    SampleType cutoffFreqHz { SampleType (200) };
    SampleType resonance;
 
    SampleType cutoffFreqScaler;
 
    Mode mode;
    bool enabled = true;
};
 
} // namespace juce::dsp