tracktion_BeatDetect.h

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 /*
    ,--.                     ,--.     ,--.  ,--.
  ,-'  '-.,--.--.,--,--.,---.|  |,-.,-'  '-.`--' ,---. ,--,--,      Copyright 2024
  '-.  .-'|  .--' ,-.  | .--'|     /'-.  .-',--.| .-. ||      \   Tracktion Software
    |  |  |  |  \ '-'  \ `--.|  \  \  |  |  |  |' '-' '|  ||  |       Corporation
    `---' `--'   `--`--'`---'`--'`--' `---' `--' `---' `--''--'    www.tracktion.com
 
    Tracktion Engine uses a GPL/commercial licence - see LICENCE.md for details.
*/
 
namespace tracktion { inline namespace engine
{
 
struct BeatDetect
{
    BeatDetect() = default;
 
    void setSampleRate (double sampleRate)
    {
        blockSize = juce::roundToInt (sampleRate / 43.06640625);
    }
 
    void setSensitivity (double newSensitivity)
    {
        const double C_MIN = 0.8f;
        const double C_MAX = 4.0f;
 
        sensitivity = C_MIN + newSensitivity * (C_MAX - C_MIN);
    }
 
    template <typename Buffer>
    void audioProcess (const Buffer& buffer)
    {
        double blockEnergy = 0;
        auto size = buffer.getSize();
 
        for (decltype (size.numChannels) chan = 0; chan < size.numChannels; ++chan)
        {
            auto d = buffer.getIterator (chan);
 
            for (decltype (size.numFrames) i = 0; i < size.numFrames; ++i)
            {
                auto sample = static_cast<double> (*d);
                blockEnergy += sample * sample;
                ++d;
            }
        }
 
        pushEnergy (blockEnergy);
    }
 
    SampleCount getBlockSize() const                    { return blockSize; }
    const juce::Array<SampleCount>& getBeats() const    { return beatSamples; }
 
private:
    static constexpr int historyLength = 43;
    double energy[historyLength] = {};
    int curBlock = 0, lastBlock = -2;
    SampleCount blockSize = 0;
    juce::Array<SampleCount> beatSamples;
    double sensitivity = 0;
 
    void pushEnergy (double e)
    {
        if (curBlock < historyLength)
        {
            energy[curBlock++] = e;
 
            if (curBlock == historyLength)
            {
                auto ave = getAverageEnergy();
 
                for (int i = 0; i < historyLength; ++i)
                    if (energy[i] > sensitivity * ave)
                        addBlock(i);
            }
        }
        else
        {
            energy[curBlock % historyLength] = e;
 
            if (e > sensitivity * getAverageEnergy())
                addBlock(curBlock);
 
            curBlock++;
        }
    }
 
    void addBlock (int i)
    {
        if (i - 1 != lastBlock)
            beatSamples.add (i * blockSize);
 
        lastBlock = i;
    }
 
    double getAverageEnergy() const noexcept
    {
        double total = 0;
 
        for (auto e : energy)
            total += e;
 
        return total / historyLength;
    }
 
    JUCE_DECLARE_NON_COPYABLE_WITH_LEAK_DETECTOR (BeatDetect)
};
 
}} // namespace tracktion { inline namespace engine