beamgrid/Source/Analyser.cpp

#include "Analyser.h"

#include <cmath>

Analyser::Analyser() = default;

void Analyser::prepare (double newSampleRate, int /*blockSize*/)
{
    sampleRate = newSampleRate > 0.0 ? newSampleRate : 44100.0;

    minFreq = 20.0;
    maxFreq = juce::jmin (20000.0, sampleRate * 0.5);

    computeBandEdges();
}

void Analyser::computeBandEdges()
{
    const int n = numBands;

    // Log-spaced band edges mapped into FFT bins.
    for (int b = 0; b <= n; ++b)
    {
        const double freq = minFreq * std::pow (maxFreq / minFreq,
                                                static_cast<double> (b) / n);
        int bin = static_cast<int> (std::round (freq * fftSize / sampleRate));
        bin = juce::jlimit (1, static_cast<int> (fftBins), bin);
        bandBinEdges[b] = bin;
    }

    // Guarantee strictly increasing edges.
    for (int b = 1; b <= n; ++b)
        if (bandBinEdges[b] <= bandBinEdges[b - 1])
            bandBinEdges[b] = juce::jmin (static_cast<int> (fftBins), bandBinEdges[b - 1] + 1);
}

void Analyser::setNumBands (int n) noexcept
{
    numBands = juce::jlimit (1, maxBands, n);
    computeBandEdges();
}

void Analyser::push (const float* channelData, int numSamples)
{
    if (channelData == nullptr)
        return;

    for (int i = 0; i < numSamples; ++i)
        pushSample (channelData[i]);
}

void Analyser::pushSample (float sample)
{
    ring[writePos] = sample;
    writePos = (writePos + 1) % fftSize;
    ++totalSamples;

    // Only start transforming once the window has filled at least once,
    // then recompute overlapped every `hopSize` samples.
    if (totalSamples >= fftSize && ++samplesSinceFFT >= hopSize)
    {
        samplesSinceFFT = 0;
        computeFFT();
    }
}

void Analyser::computeFFT()
{
    // Gather the most recent fftSize samples in order (oldest -> newest).
    const int start = writePos;
    for (int i = 0; i < fftSize; ++i)
        fftData[i] = ring[(start + i) % fftSize];

    window.multiplyWithWindowingTable (fftData.data(), static_cast<size_t> (fftSize));
    juce::FloatVectorOperations::clear (fftData.data() + fftSize, fftSize);

    fft.performFrequencyOnlyForwardTransform (fftData.data());

    for (int b = 0; b < numBands; ++b)
    {
        const int lo = bandBinEdges[b];
        const int hi = bandBinEdges[b + 1];

        double sum = 0.0;
        int count = 0;
        for (int k = lo; k < hi && k < fftBins; ++k)
        {
            sum += fftData[k];
            ++count;
        }

        const double avg = count > 0 ? sum / count : 0.0;

        // Normalize the bin magnitude by the FFT size so "0 dB" corresponds
        // to ~full scale, otherwise the raw magnitudes sit ~66 dB too hot.
        const double normalized = avg / static_cast<double> (fftSize);
        const double db = 20.0 * std::log10 (normalized + 1e-9);
        double norm = (db - minDb) / (maxDb - minDb);
        norm = juce::jlimit (0.0, 1.0, norm);

        targets[b] = static_cast<float> (norm);
    }
}

void Analyser::update (double dt)
{
    // Live bar level eases toward the latest FFT target with a fast attack
    // and a knob-controlled release (bar falloff).
    const double attackCoef  = 1.0 - std::exp (-dt / 0.005);
    const double releaseCoef = 1.0 - std::exp (-dt / juce::jmax (0.001, barReleaseTau));

    for (int b = 0; b < numBands; ++b)
    {
        const float target = targets[b];

        if (target >= levels[b])
            levels[b] += (target - levels[b]) * static_cast<float> (attackCoef);
        else
            levels[b] += (target - levels[b]) * static_cast<float> (releaseCoef);

        if (levels[b] >= peaks[b])
        {
            peaks[b] = levels[b];
            peakTimers[b] = 0.0f;
        }
        else
        {
            peakTimers[b] += static_cast<float> (dt);

            if (peakTimers[b] >= grace)
            {
                peaks[b] -= static_cast<float> (falloffRate * dt);

                if (peaks[b] < levels[b])
                    peaks[b] = levels[b];
                if (peaks[b] < 0.0f)
                    peaks[b] = 0.0f;
            }
        }
    }
}

float Analyser::freqToFraction (double freq) const noexcept
{
    const double f = juce::jlimit (minFreq, maxFreq, freq);
    return static_cast<float> (std::log (f / minFreq) / std::log (maxFreq / minFreq));
}

float Analyser::dbToFraction (double db) const noexcept
{
    return static_cast<float> (juce::jlimit (0.0, 1.0, (db - minDb) / (maxDb - minDb)));
}