juce_LinkwitzRileyFilter.h

/*
  ==============================================================================
 
   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 LinkwitzRileyFilterType
{
    lowpass,
    highpass,
    allpass
};

template <typename SampleType>
class LinkwitzRileyFilter
{
public:
    //==============================================================================
    using Type = LinkwitzRileyFilterType;
 
    //==============================================================================
    LinkwitzRileyFilter();
 
    //==============================================================================
    void setType (Type newType);

    void setCutoffFrequency (SampleType newCutoffFrequencyHz);
 
    //==============================================================================
    Type getType() const noexcept                      { return filterType; }

    SampleType getCutoffFrequency() const noexcept     { return cutoffFrequency; }
 
    //==============================================================================
    void prepare (const ProcessSpec& spec);

    void reset();
 
    //==============================================================================
    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() <= s1.size());
        jassert (inputBlock.getNumChannels() == numChannels);
        jassert (inputBlock.getNumSamples()  == numSamples);
 
        if (context.isBypassed)
        {
            outputBlock.copyFrom (inputBlock);
            return;
        }
 
        for (size_t channel = 0; channel < numChannels; ++channel)
        {
            auto* inputSamples = inputBlock.getChannelPointer (channel);
            auto* outputSamples = outputBlock.getChannelPointer (channel);
 
            for (size_t i = 0; i < numSamples; ++i)
                outputSamples[i] = processSample ((int) channel, inputSamples[i]);
        }
 
       #if JUCE_DSP_ENABLE_SNAP_TO_ZERO
        snapToZero();
       #endif
    }

    SampleType processSample (int channel, SampleType inputValue);

    void processSample (int channel, SampleType inputValue, SampleType &outputLow, SampleType &outputHigh);

    void snapToZero() noexcept;
 
private:
    //==============================================================================
    void update();
 
    //==============================================================================
    SampleType g, R2, h;
    std::vector<SampleType> s1, s2, s3, s4;
 
    double sampleRate = 44100.0;
    SampleType cutoffFrequency = 2000.0;
    Type filterType = Type::lowpass;
};
 
} // namespace juce::dsp