juce_Oversampling.cpp

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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
{
 
template <typename SampleType>
struct Oversampling<SampleType>::OversamplingStage
{
    OversamplingStage (size_t numChans, size_t newFactor)  : numChannels (numChans), factor (newFactor) {}
    virtual ~OversamplingStage() {}
 
    //==============================================================================
    virtual SampleType getLatencyInSamples() const = 0;
 
    virtual void initProcessing (size_t maximumNumberOfSamplesBeforeOversampling)
    {
        buffer.setSize (static_cast<int> (numChannels),
                        static_cast<int> (maximumNumberOfSamplesBeforeOversampling * factor),
                        false, false, true);
    }
 
    virtual void reset()
    {
        buffer.clear();
    }
 
    AudioBlock<SampleType> getProcessedSamples (size_t numSamples)
    {
        return AudioBlock<SampleType> (buffer).getSubBlock (0, numSamples);
    }
 
    virtual void processSamplesUp   (const AudioBlock<const SampleType>&) = 0;
    virtual void processSamplesDown (AudioBlock<SampleType>&) = 0;
 
    AudioBuffer<SampleType> buffer;
    size_t numChannels, factor;
};
 
 
//==============================================================================
template <typename SampleType>
struct OversamplingDummy final : public Oversampling<SampleType>::OversamplingStage
{
    using ParentType = typename Oversampling<SampleType>::OversamplingStage;
 
    OversamplingDummy (size_t numChans) : ParentType (numChans, 1) {}
 
    //==============================================================================
    SampleType getLatencyInSamples() const override
    {
        return 0;
    }
 
    void processSamplesUp (const AudioBlock<const SampleType>& inputBlock) override
    {
        jassert (inputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (inputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        for (size_t channel = 0; channel < inputBlock.getNumChannels(); ++channel)
            ParentType::buffer.copyFrom (static_cast<int> (channel), 0,
                inputBlock.getChannelPointer (channel), static_cast<int> (inputBlock.getNumSamples()));
    }
 
    void processSamplesDown (AudioBlock<SampleType>& outputBlock) override
    {
        jassert (outputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (outputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        outputBlock.copyFrom (ParentType::getProcessedSamples (outputBlock.getNumSamples()));
    }
 
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (OversamplingDummy)
};
 
//==============================================================================
template <typename SampleType>
struct Oversampling2TimesEquirippleFIR final : public Oversampling<SampleType>::OversamplingStage
{
    using ParentType = typename Oversampling<SampleType>::OversamplingStage;
 
    Oversampling2TimesEquirippleFIR (size_t numChans,
                                     SampleType normalisedTransitionWidthUp,
                                     SampleType stopbandAmplitudedBUp,
                                     SampleType normalisedTransitionWidthDown,
                                     SampleType stopbandAmplitudedBDown)
        : ParentType (numChans, 2)
    {
        coefficientsUp   = *FilterDesign<SampleType>::designFIRLowpassHalfBandEquirippleMethod (normalisedTransitionWidthUp,   stopbandAmplitudedBUp);
        coefficientsDown = *FilterDesign<SampleType>::designFIRLowpassHalfBandEquirippleMethod (normalisedTransitionWidthDown, stopbandAmplitudedBDown);
 
        auto N = coefficientsUp.getFilterOrder() + 1;
        stateUp.setSize (static_cast<int> (this->numChannels), static_cast<int> (N));
 
        N = coefficientsDown.getFilterOrder() + 1;
        auto Ndiv2 = N / 2;
        auto Ndiv4 = Ndiv2 / 2;
 
        stateDown.setSize  (static_cast<int> (this->numChannels), static_cast<int> (N));
        stateDown2.setSize (static_cast<int> (this->numChannels), static_cast<int> (Ndiv4 + 1));
 
        position.resize (static_cast<int> (this->numChannels));
    }
 
    //==============================================================================
    SampleType getLatencyInSamples() const override
    {
        return static_cast<SampleType> (coefficientsUp.getFilterOrder() + coefficientsDown.getFilterOrder()) * 0.5f;
    }
 
    void reset() override
    {
        ParentType::reset();
 
        stateUp.clear();
        stateDown.clear();
        stateDown2.clear();
 
        position.fill (0);
    }
 
    void processSamplesUp (const AudioBlock<const SampleType>& inputBlock) override
    {
        jassert (inputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (inputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        // Initialization
        auto fir = coefficientsUp.getRawCoefficients();
        auto N = coefficientsUp.getFilterOrder() + 1;
        auto Ndiv2 = N / 2;
        auto numSamples = inputBlock.getNumSamples();
 
        // Processing
        for (size_t channel = 0; channel < inputBlock.getNumChannels(); ++channel)
        {
            auto bufferSamples = ParentType::buffer.getWritePointer (static_cast<int> (channel));
            auto buf = stateUp.getWritePointer (static_cast<int> (channel));
            auto samples = inputBlock.getChannelPointer (channel);
 
            for (size_t i = 0; i < numSamples; ++i)
            {
                // Input
                buf[N - 1] = 2 * samples[i];
 
                // Convolution
                auto out = static_cast<SampleType> (0.0);
 
                for (size_t k = 0; k < Ndiv2; k += 2)
                    out += (buf[k] + buf[N - k - 1]) * fir[k];
 
                // Outputs
                bufferSamples[i << 1] = out;
                bufferSamples[(i << 1) + 1] = buf[Ndiv2 + 1] * fir[Ndiv2];
 
                // Shift data
                for (size_t k = 0; k < N - 2; k += 2)
                    buf[k] = buf[k + 2];
            }
        }
    }
 
    void processSamplesDown (AudioBlock<SampleType>& outputBlock) override
    {
        jassert (outputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (outputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        // Initialization
        auto fir = coefficientsDown.getRawCoefficients();
        auto N = coefficientsDown.getFilterOrder() + 1;
        auto Ndiv2 = N / 2;
        auto Ndiv4 = Ndiv2 / 2;
        auto numSamples = outputBlock.getNumSamples();
 
        // Processing
        for (size_t channel = 0; channel < outputBlock.getNumChannels(); ++channel)
        {
            auto bufferSamples = ParentType::buffer.getWritePointer (static_cast<int> (channel));
            auto buf = stateDown.getWritePointer (static_cast<int> (channel));
            auto buf2 = stateDown2.getWritePointer (static_cast<int> (channel));
            auto samples = outputBlock.getChannelPointer (channel);
            auto pos = position.getUnchecked (static_cast<int> (channel));
 
            for (size_t i = 0; i < numSamples; ++i)
            {
                // Input
                buf[N - 1] = bufferSamples[i << 1];
 
                // Convolution
                auto out = static_cast<SampleType> (0.0);
 
                for (size_t k = 0; k < Ndiv2; k += 2)
                    out += (buf[k] + buf[N - k - 1]) * fir[k];
 
                // Output
                out += buf2[pos] * fir[Ndiv2];
                buf2[pos] = bufferSamples[(i << 1) + 1];
 
                samples[i] = out;
 
                // Shift data
                for (size_t k = 0; k < N - 2; ++k)
                    buf[k] = buf[k + 2];
 
                // Circular buffer
                pos = (pos == 0 ? Ndiv4 : pos - 1);
            }
 
            position.setUnchecked (static_cast<int> (channel), pos);
        }
 
    }
 
private:
    //==============================================================================
    FIR::Coefficients<SampleType> coefficientsUp, coefficientsDown;
    AudioBuffer<SampleType> stateUp, stateDown, stateDown2;
    Array<size_t> position;
 
    //==============================================================================
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (Oversampling2TimesEquirippleFIR)
};
 
 
//==============================================================================
template <typename SampleType>
struct Oversampling2TimesPolyphaseIIR final : public Oversampling<SampleType>::OversamplingStage
{
    using ParentType = typename Oversampling<SampleType>::OversamplingStage;
 
    Oversampling2TimesPolyphaseIIR (size_t numChans,
                                    SampleType normalisedTransitionWidthUp,
                                    SampleType stopbandAmplitudedBUp,
                                    SampleType normalisedTransitionWidthDown,
                                    SampleType stopbandAmplitudedBDown)
        : ParentType (numChans, 2)
    {
        auto structureUp = FilterDesign<SampleType>::designIIRLowpassHalfBandPolyphaseAllpassMethod (normalisedTransitionWidthUp, stopbandAmplitudedBUp);
        auto coeffsUp = getCoefficients (structureUp);
        latency = static_cast<SampleType> (-(coeffsUp.getPhaseForFrequency (0.0001, 1.0)) / (0.0001 * MathConstants<double>::twoPi));
 
        auto structureDown = FilterDesign<SampleType>::designIIRLowpassHalfBandPolyphaseAllpassMethod (normalisedTransitionWidthDown, stopbandAmplitudedBDown);
        auto coeffsDown = getCoefficients (structureDown);
        latency += static_cast<SampleType> (-(coeffsDown.getPhaseForFrequency (0.0001, 1.0)) / (0.0001 * MathConstants<double>::twoPi));
 
        for (auto i = 0; i < structureUp.directPath.size(); ++i)
            coefficientsUp.add (structureUp.directPath.getObjectPointer (i)->coefficients[0]);
 
        for (auto i = 1; i < structureUp.delayedPath.size(); ++i)
            coefficientsUp.add (structureUp.delayedPath.getObjectPointer (i)->coefficients[0]);
 
        for (auto i = 0; i < structureDown.directPath.size(); ++i)
            coefficientsDown.add (structureDown.directPath.getObjectPointer (i)->coefficients[0]);
 
        for (auto i = 1; i < structureDown.delayedPath.size(); ++i)
            coefficientsDown.add (structureDown.delayedPath.getObjectPointer (i)->coefficients[0]);
 
        v1Up.setSize   (static_cast<int> (this->numChannels), coefficientsUp.size());
        v1Down.setSize (static_cast<int> (this->numChannels), coefficientsDown.size());
        delayDown.resize (static_cast<int> (this->numChannels));
    }
 
    //==============================================================================
    SampleType getLatencyInSamples() const override
    {
        return latency;
    }
 
    void reset() override
    {
        ParentType::reset();
        v1Up.clear();
        v1Down.clear();
        delayDown.fill (0);
    }
 
    void processSamplesUp (const AudioBlock<const SampleType>& inputBlock) override
    {
        jassert (inputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (inputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        // Initialization
        auto coeffs = coefficientsUp.getRawDataPointer();
        auto numStages = coefficientsUp.size();
        auto delayedStages = numStages / 2;
        auto directStages = numStages - delayedStages;
        auto numSamples = inputBlock.getNumSamples();
 
        // Processing
        for (size_t channel = 0; channel < inputBlock.getNumChannels(); ++channel)
        {
            auto bufferSamples = ParentType::buffer.getWritePointer (static_cast<int> (channel));
            auto lv1 = v1Up.getWritePointer (static_cast<int> (channel));
            auto samples = inputBlock.getChannelPointer (channel);
 
            for (size_t i = 0; i < numSamples; ++i)
            {
                // Direct path cascaded allpass filters
                auto input = samples[i];
 
                for (auto n = 0; n < directStages; ++n)
                {
                    auto alpha = coeffs[n];
                    auto output = alpha * input + lv1[n];
                    lv1[n] = input - alpha * output;
                    input = output;
                }
 
                // Output
                bufferSamples[i << 1] = input;
 
                // Delayed path cascaded allpass filters
                input = samples[i];
 
                for (auto n = directStages; n < numStages; ++n)
                {
                    auto alpha = coeffs[n];
                    auto output = alpha * input + lv1[n];
                    lv1[n] = input - alpha * output;
                    input = output;
                }
 
                // Output
                bufferSamples[(i << 1) + 1] = input;
            }
        }
 
       #if JUCE_DSP_ENABLE_SNAP_TO_ZERO
        snapToZero (true);
       #endif
    }
 
    void processSamplesDown (AudioBlock<SampleType>& outputBlock) override
    {
        jassert (outputBlock.getNumChannels() <= static_cast<size_t> (ParentType::buffer.getNumChannels()));
        jassert (outputBlock.getNumSamples() * ParentType::factor <= static_cast<size_t> (ParentType::buffer.getNumSamples()));
 
        // Initialization
        auto coeffs = coefficientsDown.getRawDataPointer();
        auto numStages = coefficientsDown.size();
        auto delayedStages = numStages / 2;
        auto directStages = numStages - delayedStages;
        auto numSamples = outputBlock.getNumSamples();
 
        // Processing
        for (size_t channel = 0; channel < outputBlock.getNumChannels(); ++channel)
        {
            auto bufferSamples = ParentType::buffer.getWritePointer (static_cast<int> (channel));
            auto lv1 = v1Down.getWritePointer (static_cast<int> (channel));
            auto samples = outputBlock.getChannelPointer (channel);
            auto delay = delayDown.getUnchecked (static_cast<int> (channel));
 
            for (size_t i = 0; i < numSamples; ++i)
            {
                // Direct path cascaded allpass filters
                auto input = bufferSamples[i << 1];
 
                for (auto n = 0; n < directStages; ++n)
                {
                    auto alpha = coeffs[n];
                    auto output = alpha * input + lv1[n];
                    lv1[n] = input - alpha * output;
                    input = output;
                }
 
                auto directOut = input;
 
                // Delayed path cascaded allpass filters
                input = bufferSamples[(i << 1) + 1];
 
                for (auto n = directStages; n < numStages; ++n)
                {
                    auto alpha = coeffs[n];
                    auto output = alpha * input + lv1[n];
                    lv1[n] = input - alpha * output;
                    input = output;
                }
 
                // Output
                samples[i] = (delay + directOut) * static_cast<SampleType> (0.5);
                delay = input;
            }
 
            delayDown.setUnchecked (static_cast<int> (channel), delay);
        }
 
       #if JUCE_DSP_ENABLE_SNAP_TO_ZERO
        snapToZero (false);
       #endif
    }
 
    void snapToZero (bool snapUpProcessing)
    {
        if (snapUpProcessing)
        {
            for (auto channel = 0; channel < ParentType::buffer.getNumChannels(); ++channel)
            {
                auto lv1 = v1Up.getWritePointer (channel);
                auto numStages = coefficientsUp.size();
 
                for (auto n = 0; n < numStages; ++n)
                    util::snapToZero (lv1[n]);
            }
        }
        else
        {
            for (auto channel = 0; channel < ParentType::buffer.getNumChannels(); ++channel)
            {
                auto lv1 = v1Down.getWritePointer (channel);
                auto numStages = coefficientsDown.size();
 
                for (auto n = 0; n < numStages; ++n)
                    util::snapToZero (lv1[n]);
            }
        }
    }
 
private:
    //==============================================================================
    IIR::Coefficients<SampleType> getCoefficients (typename FilterDesign<SampleType>::IIRPolyphaseAllpassStructure& structure) const
    {
        constexpr auto one = static_cast<SampleType> (1.0);
 
        Polynomial<SampleType> numerator1 ({ one }), denominator1 ({ one }),
                               numerator2 ({ one }), denominator2 ({ one });
 
        for (auto* i : structure.directPath)
        {
            auto coeffs = i->getRawCoefficients();
 
            if (i->getFilterOrder() == 1)
            {
                numerator1   = numerator1  .getProductWith (Polynomial<SampleType> ({ coeffs[0], coeffs[1] }));
                denominator1 = denominator1.getProductWith (Polynomial<SampleType> ({ one,       coeffs[2] }));
            }
            else
            {
                numerator1   = numerator1  .getProductWith (Polynomial<SampleType> ({ coeffs[0], coeffs[1], coeffs[2] }));
                denominator1 = denominator1.getProductWith (Polynomial<SampleType> ({ one,       coeffs[3], coeffs[4] }));
            }
        }
 
        for (auto* i : structure.delayedPath)
        {
            auto coeffs = i->getRawCoefficients();
 
            if (i->getFilterOrder() == 1)
            {
                numerator2   = numerator2  .getProductWith (Polynomial<SampleType> ({ coeffs[0], coeffs[1] }));
                denominator2 = denominator2.getProductWith (Polynomial<SampleType> ({ one,       coeffs[2] }));
            }
            else
            {
                numerator2   = numerator2  .getProductWith (Polynomial<SampleType> ({ coeffs[0], coeffs[1], coeffs[2] }));
                denominator2 = denominator2.getProductWith (Polynomial<SampleType> ({ one,       coeffs[3], coeffs[4] }));
            }
        }
 
        auto numeratorf1 = numerator1.getProductWith (denominator2);
        auto numeratorf2 = numerator2.getProductWith (denominator1);
        auto numerator   = numeratorf1.getSumWith (numeratorf2);
        auto denominator = denominator1.getProductWith (denominator2);
 
        IIR::Coefficients<SampleType> coeffs;
 
        coeffs.coefficients.clear();
        auto inversion = one / denominator[0];
 
        for (int i = 0; i <= numerator.getOrder(); ++i)
            coeffs.coefficients.add (numerator[i] * inversion);
 
        for (int i = 1; i <= denominator.getOrder(); ++i)
            coeffs.coefficients.add (denominator[i] * inversion);
 
        return coeffs;
    }
 
    //==============================================================================
    Array<SampleType> coefficientsUp, coefficientsDown;
    SampleType latency;
 
    AudioBuffer<SampleType> v1Up, v1Down;
    Array<SampleType> delayDown;
 
    //==============================================================================
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (Oversampling2TimesPolyphaseIIR)
};
 
 
//==============================================================================
template <typename SampleType>
Oversampling<SampleType>::Oversampling (size_t newNumChannels)
    : numChannels (newNumChannels)
{
    jassert (numChannels > 0);
 
    addDummyOversamplingStage();
}
 
template <typename SampleType>
Oversampling<SampleType>::Oversampling (size_t newNumChannels, size_t newFactor,
                                        FilterType newType, bool isMaximumQuality,
                                        bool useIntegerLatency)
    : numChannels (newNumChannels), shouldUseIntegerLatency (useIntegerLatency)
{
    jassert (isPositiveAndBelow (newFactor, 5) && numChannels > 0);
 
    if (newFactor == 0)
    {
        addDummyOversamplingStage();
    }
    else if (newType == FilterType::filterHalfBandPolyphaseIIR)
    {
        for (size_t n = 0; n < newFactor; ++n)
        {
            auto twUp   = (isMaximumQuality ? 0.10f : 0.12f) * (n == 0 ? 0.5f : 1.0f);
            auto twDown = (isMaximumQuality ? 0.12f : 0.15f) * (n == 0 ? 0.5f : 1.0f);
 
            auto gaindBStartUp    = (isMaximumQuality ? -90.0f : -70.0f);
            auto gaindBStartDown  = (isMaximumQuality ? -75.0f : -60.0f);
            auto gaindBFactorUp   = (isMaximumQuality ? 10.0f  : 8.0f);
            auto gaindBFactorDown = (isMaximumQuality ? 10.0f  : 8.0f);
 
            addOversamplingStage (FilterType::filterHalfBandPolyphaseIIR,
                                  twUp, gaindBStartUp + gaindBFactorUp * (float) n,
                                  twDown, gaindBStartDown + gaindBFactorDown * (float) n);
        }
    }
    else if (newType == FilterType::filterHalfBandFIREquiripple)
    {
        for (size_t n = 0; n < newFactor; ++n)
        {
            auto twUp   = (isMaximumQuality ? 0.10f : 0.12f) * (n == 0 ? 0.5f : 1.0f);
            auto twDown = (isMaximumQuality ? 0.12f : 0.15f) * (n == 0 ? 0.5f : 1.0f);
 
            auto gaindBStartUp    = (isMaximumQuality ? -90.0f : -70.0f);
            auto gaindBStartDown  = (isMaximumQuality ? -75.0f : -60.0f);
            auto gaindBFactorUp   = (isMaximumQuality ? 10.0f  : 8.0f);
            auto gaindBFactorDown = (isMaximumQuality ? 10.0f  : 8.0f);
 
            addOversamplingStage (FilterType::filterHalfBandFIREquiripple,
                                  twUp, gaindBStartUp + gaindBFactorUp * (float) n,
                                  twDown, gaindBStartDown + gaindBFactorDown * (float) n);
        }
    }
}
 
template <typename SampleType>
Oversampling<SampleType>::~Oversampling()
{
    stages.clear();
}
 
//==============================================================================
template <typename SampleType>
void Oversampling<SampleType>::addDummyOversamplingStage()
{
    stages.add (new OversamplingDummy<SampleType> (numChannels));
}
 
template <typename SampleType>
void Oversampling<SampleType>::addOversamplingStage (FilterType type,
                                                     float normalisedTransitionWidthUp,
                                                     float stopbandAmplitudedBUp,
                                                     float normalisedTransitionWidthDown,
                                                     float stopbandAmplitudedBDown)
{
    if (type == FilterType::filterHalfBandPolyphaseIIR)
    {
        stages.add (new Oversampling2TimesPolyphaseIIR<SampleType> (numChannels,
                                                                    normalisedTransitionWidthUp,   stopbandAmplitudedBUp,
                                                                    normalisedTransitionWidthDown, stopbandAmplitudedBDown));
    }
    else
    {
        stages.add (new Oversampling2TimesEquirippleFIR<SampleType> (numChannels,
                                                                     normalisedTransitionWidthUp,   stopbandAmplitudedBUp,
                                                                     normalisedTransitionWidthDown, stopbandAmplitudedBDown));
    }
 
    factorOversampling *= 2;
}
 
template <typename SampleType>
void Oversampling<SampleType>::clearOversamplingStages()
{
    stages.clear();
    factorOversampling = 1u;
}
 
//==============================================================================
template <typename SampleType>
void Oversampling<SampleType>::setUsingIntegerLatency (bool useIntegerLatency) noexcept
{
    shouldUseIntegerLatency = useIntegerLatency;
}
 
template <typename SampleType>
SampleType Oversampling<SampleType>::getLatencyInSamples() const noexcept
{
    auto latency = getUncompensatedLatency();
    return shouldUseIntegerLatency ? latency + fractionalDelay : latency;
}
 
template <typename SampleType>
SampleType Oversampling<SampleType>::getUncompensatedLatency() const noexcept
{
    auto latency = static_cast<SampleType> (0);
    size_t order = 1;
 
    for (auto* stage : stages)
    {
        order *= stage->factor;
        latency += stage->getLatencyInSamples() / static_cast<SampleType> (order);
    }
 
    return latency;
}
 
template <typename SampleType>
size_t Oversampling<SampleType>::getOversamplingFactor() const noexcept
{
    return factorOversampling;
}
 
//==============================================================================
template <typename SampleType>
void Oversampling<SampleType>::initProcessing (size_t maximumNumberOfSamplesBeforeOversampling)
{
    jassert (! stages.isEmpty());
    auto currentNumSamples = maximumNumberOfSamplesBeforeOversampling;
 
    for (auto* stage : stages)
    {
        stage->initProcessing (currentNumSamples);
        currentNumSamples *= stage->factor;
    }
 
    ProcessSpec spec = { 0.0, (uint32) maximumNumberOfSamplesBeforeOversampling, (uint32) numChannels };
    delay.prepare (spec);
    updateDelayLine();
 
    isReady = true;
    reset();
}
 
template <typename SampleType>
void Oversampling<SampleType>::reset() noexcept
{
    jassert (! stages.isEmpty());
 
    if (isReady)
        for (auto* stage : stages)
           stage->reset();
 
    delay.reset();
}
 
template <typename SampleType>
AudioBlock<SampleType> Oversampling<SampleType>::processSamplesUp (const AudioBlock<const SampleType>& inputBlock) noexcept
{
    jassert (! stages.isEmpty());
 
    if (! isReady)
        return {};
 
    auto* firstStage = stages.getUnchecked (0);
    firstStage->processSamplesUp (inputBlock);
    auto block = firstStage->getProcessedSamples (inputBlock.getNumSamples() * firstStage->factor);
 
    for (int i = 1; i < stages.size(); ++i)
    {
        stages[i]->processSamplesUp (block);
        block = stages[i]->getProcessedSamples (block.getNumSamples() * stages[i]->factor);
    }
 
    return block;
}
 
template <typename SampleType>
void Oversampling<SampleType>::processSamplesDown (AudioBlock<SampleType>& outputBlock) noexcept
{
    jassert (! stages.isEmpty());
 
    if (! isReady)
        return;
 
    auto currentNumSamples = outputBlock.getNumSamples();
 
    for (int n = 0; n < stages.size() - 1; ++n)
        currentNumSamples *= stages.getUnchecked (n)->factor;
 
    for (int n = stages.size() - 1; n > 0; --n)
    {
        auto& stage = *stages.getUnchecked (n);
        auto audioBlock = stages.getUnchecked (n - 1)->getProcessedSamples (currentNumSamples);
        stage.processSamplesDown (audioBlock);
 
        currentNumSamples /= stage.factor;
    }
 
    stages.getFirst()->processSamplesDown (outputBlock);
 
    if (shouldUseIntegerLatency && fractionalDelay > static_cast<SampleType> (0.0))
    {
        auto context = ProcessContextReplacing<SampleType> (outputBlock);
        delay.process (context);
    }
}
 
template <typename SampleType>
void Oversampling<SampleType>::updateDelayLine()
{
    auto latency = getUncompensatedLatency();
    fractionalDelay = static_cast<SampleType> (1.0) - (latency - std::floor (latency));
 
    if (approximatelyEqual (fractionalDelay, static_cast<SampleType> (1.0)))
        fractionalDelay = static_cast<SampleType> (0.0);
    else if (fractionalDelay < static_cast<SampleType> (0.618))
        fractionalDelay += static_cast<SampleType> (1.0);
 
    delay.setDelay (fractionalDelay);
}
 
template class Oversampling<float>;
template class Oversampling<double>;
 
} // namespace juce::dsp