JUCE/modules/juce_dsp/widgets/juce_Chorus.h

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

namespace juce::dsp
{

/**
    A simple chorus DSP widget that modulates the delay of a delay line in order to
    create sweeping notches in the magnitude frequency response.

    This audio effect can be controlled via the speed and depth of the LFO controlling
    the frequency response, a mix control, a feedback control, and the centre delay
    of the modulation.

    Note: To get classic chorus sounds try to use a centre delay time around 7-8 ms
    with a low feedback volume and a low depth. This effect can also be used as a
    flanger with a lower centre delay time and a lot of feedback, and as a vibrato
    effect if the mix value is 1.

    @tags{DSP}
*/
template <typename SampleType>
class Chorus
{
public:
    //==============================================================================
    /** Constructor. */
    Chorus();

    //==============================================================================
    /** Sets the rate (in Hz) of the LFO modulating the chorus delay line. This rate
        must be lower than 100 Hz.
    */
    void setRate (SampleType newRateHz);

    /** Sets the volume of the LFO modulating the chorus delay line (between 0 and 1).
    */
    void setDepth (SampleType newDepth);

    /** Sets the centre delay in milliseconds of the chorus delay line modulation.
        This delay must be between 1 and 100 ms.
    */
    void setCentreDelay (SampleType newDelayMs);

    /** Sets the feedback volume (between -1 and 1) of the chorus delay line.
        Negative values can be used to get specific chorus sounds.
    */
    void setFeedback (SampleType newFeedback);

    /** Sets the amount of dry and wet signal in the output of the chorus (between 0
        for full dry and 1 for full wet).
    */
    void setMix (SampleType newMix);

    //==============================================================================
    /** Initialises the processor. */
    void prepare (const ProcessSpec& spec);

    /** Resets the internal state variables of the processor. */
    void reset();

    //==============================================================================
    /** Processes the input and output samples supplied in the processing context. */
    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() == numChannels);
        jassert (inputBlock.getNumChannels() == lastOutput.size());
        jassert (inputBlock.getNumSamples()  == numSamples);

        if (context.isBypassed)
        {
            outputBlock.copyFrom (inputBlock);
            return;
        }

        auto delayValuesBlock = AudioBlock<SampleType> (bufferDelayTimes).getSubBlock (0, numSamples);
        auto contextDelay = ProcessContextReplacing<SampleType> (delayValuesBlock);
        delayValuesBlock.clear();

        osc.process (contextDelay);
        delayValuesBlock.multiplyBy (oscVolume);

        auto* delaySamples = bufferDelayTimes.getWritePointer (0);

        for (size_t i = 0; i < numSamples; ++i)
        {
            auto lfo = jmax (static_cast<SampleType> (1.0), maximumDelayModulation * delaySamples[i] + centreDelay);
            delaySamples[i] = static_cast<SampleType> (lfo * sampleRate / 1000.0);
        }

        dryWet.pushDrySamples (inputBlock);

        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)
            {
                auto input = inputSamples[i];
                auto output = input - lastOutput[channel];

                delay.pushSample ((int) channel, output);
                delay.setDelay (delaySamples[i]);
                output = delay.popSample ((int) channel);

                outputSamples[i] = output;
                lastOutput[channel] = output * feedbackVolume[channel].getNextValue();
            }
        }

        dryWet.mixWetSamples (outputBlock);
    }

private:
    //==============================================================================
    void update();

    //==============================================================================
    Oscillator<SampleType> osc;
    DelayLine<SampleType, DelayLineInterpolationTypes::Linear> delay;
    SmoothedValue<SampleType, ValueSmoothingTypes::Linear> oscVolume;
    std::vector<SmoothedValue<SampleType, ValueSmoothingTypes::Linear>> feedbackVolume { 2 };
    DryWetMixer<SampleType> dryWet;
    std::vector<SampleType> lastOutput { 2 };
    AudioBuffer<SampleType> bufferDelayTimes;

    double sampleRate = 44100.0;
    SampleType rate = 1.0, depth = 0.25, feedback = 0.0, mix = 0.5,
               centreDelay = 7.0;

    static constexpr SampleType maxDepth               = 1.0,
                                maxCentreDelayMs       = 100.0,
                                oscVolumeMultiplier    = 0.5,
                                maximumDelayModulation = 20.0;
};

} // namespace juce::dsp