monostep/Source/dsp/FxProcessor.cpp

#include "FxProcessor.h"

#include <algorithm>
#include <cmath>

namespace monostep
{

// Freeverb-style comb / allpass sizes, slightly offset per channel so the
// left and right reverb tails decorrelate. Halved from the classic freeverb
// set so the early reflections land ~13 ms after the note instead of ~25 ms:
// a 100%-wet reverb keeps its tail but speaks much sooner.
static constexpr int combSizes[2][4] =
{
    { 558, 594, 639, 678 },
    { 563, 599, 644, 683 }
};

static constexpr int allpassSizes[2][2] =
{
    { 113, 278 },
    { 118, 283 }
};

float FxProcessor::delayTimeSeconds (float knob, bool sync, double bpm)
{
    if (sync)
    {
        static const float divisions[] = { 0.25f, 0.5f, 0.75f, 1.0f, 1.5f, 2.0f, 3.0f, 4.0f };
        const int idx = juce::roundToInt (juce::jlimit (0.0f, 1.0f, knob) * 7.0f);
        return divisions[juce::jlimit (0, 7, idx)] * 60.0f / (float) juce::jmax (1.0, bpm);
    }

    return 0.005f * std::pow (200.0f, juce::jlimit (0.0f, 1.0f, knob));
}

juce::String FxProcessor::delayTimeLabel (float knob, bool sync, double bpm)
{
    if (sync)
    {
        static const char* names[] = { "1/16", "1/8", "3/16", "1/4", "3/8", "1/2", "3/4", "1 bar" };
        const int idx = juce::roundToInt (juce::jlimit (0.0f, 1.0f, knob) * 7.0f);
        return names[juce::jlimit (0, 7, idx)];
    }

    return juce::String (juce::roundToInt (delayTimeSeconds (knob, false, bpm) * 1000.0f)) + " ms";
}

void FxProcessor::prepare (double sr, int channels)
{
    sampleRate = juce::jmax (44100.0, sr);
    numChannels = juce::jmax (1, channels);

    maxDelaySamples = (int) (sampleRate * 2.0);

    delays.clear();
    delays.resize (numChannels);
    for (auto& d : delays)
    {
        d.memory.assign ((size_t) maxDelaySamples + 8, 0.0f);
        d.writeIndex = 0;
        d.smoothedDelay = 0.0f;
        d.feedbackLp = 0.0f;
    }

    const float srScale = (float) (sampleRate / 44100.0);
    for (int ch = 0; ch < 2; ++ch)
    {
        for (int i = 0; i < 4; ++i)
            combDelaySamples[ch][i] = juce::roundToInt (combSizes[ch][i] * srScale);
        for (int i = 0; i < 2; ++i)
            allpassDelaySamples[ch][i] = juce::roundToInt (allpassSizes[ch][i] * srScale);
    }

    reverbs.clear();
    reverbs.resize (numChannels);
    for (int ch = 0; ch < numChannels; ++ch)
    {
        const int rc = ch & 1;
        auto& r = reverbs[ch];

        for (int i = 0; i < 4; ++i)
            r.combs[i].assign ((size_t) combDelaySamples[rc][i], 0.0f);

        for (int i = 0; i < 2; ++i)
            r.allpasses[i].assign ((size_t) allpassDelaySamples[rc][i], 0.0f);
    }
}

void FxProcessor::reset()
{
    for (auto& d : delays)
    {
        std::fill (d.memory.begin(), d.memory.end(), 0.0f);
        d.writeIndex = 0;
        d.smoothedDelay = 0.0f;
        d.feedbackLp = 0.0f;
    }

    for (auto& r : reverbs)
    {
        for (int i = 0; i < 4; ++i)
        {
            std::fill (r.combs[i].begin(), r.combs[i].end(), 0.0f);
            r.combIndex[i] = 0;
        }
        for (int i = 0; i < 2; ++i)
        {
            std::fill (r.allpasses[i].begin(), r.allpasses[i].end(), 0.0f);
            r.allpassIndex[i] = 0;
        }
    }
}

void FxProcessor::setParams (const Params& p)
{
    params.delayTime     = juce::jlimit (0.0f, 1.0f, p.delayTime);
    params.delayFeedback = juce::jlimit (0.0f, 0.9f, p.delayFeedback);
    params.delaySync     = p.delaySync;
    params.delayMix      = juce::jlimit (0.0f, 1.0f, p.delayMix);
    params.reverbRoom    = juce::jlimit (0.0f, 1.0f, p.reverbRoom);
    params.reverbLevel   = juce::jlimit (0.0f, 1.0f, p.reverbLevel);
    params.reverbMix     = juce::jlimit (0.0f, 1.0f, p.reverbMix);
    params.reverbDiff    = juce::jlimit (0.0f, 1.0f, p.reverbDiff);
    params.bpm           = juce::jmax (20.0, p.bpm);

    currentDelaySeconds = delayTimeSeconds (params.delayTime, params.delaySync, params.bpm);
}

void FxProcessor::process (juce::AudioBuffer<float>& buffer, int numSamples)
{
    if (numSamples <= 0 || buffer.getNumChannels() == 0)
        return;

    // The reverb must feed off the dry (pre-delay) signal, not the delay's
    // output, so snapshot the incoming buffer before the delay runs.
    const bool reverbActive = params.reverbMix > 0.0001f && params.reverbLevel > 0.0001f;
    if (reverbActive)
    {
        if (dryScratch.getNumSamples() < numSamples)
            dryScratch.setSize (buffer.getNumChannels(), numSamples, false, false, true);

        const int n = juce::jmin (buffer.getNumChannels(), dryScratch.getNumChannels());
        for (int c = 0; c < n; ++c)
            dryScratch.copyFrom (c, 0, buffer, c, 0, numSamples);
    }

    processDelay (buffer, numSamples);

    if (reverbActive)
        processReverb (dryScratch, buffer, numSamples);
}

void FxProcessor::processDelay (juce::AudioBuffer<float>& buffer, int numSamples)
{
    if (params.delayMix <= 0.0001f)
        return;

    const int n = juce::jmin (numChannels, buffer.getNumChannels());
    const float targetDelay = currentDelaySeconds * (float) sampleRate;
    const float mix = params.delayMix;

    for (int ch = 0; ch < n; ++ch)
    {
        auto& d = delays[ch];
        auto* out = buffer.getWritePointer (ch);
        const int size = (int) d.memory.size();
        const int maxD = juce::jmax (1, size - 8);

        for (int i = 0; i < numSamples; ++i)
        {
            const float x = out[i];

            d.smoothedDelay += (targetDelay - d.smoothedDelay) * 0.0008f;
            const float delay = juce::jlimit (8.0f, (float) maxD, d.smoothedDelay);

            float readPos = (float) d.writeIndex - delay;
            if (readPos < 0.0f)
                readPos += (float) size;

            const int idxA = (int) readPos;
            const int idxB = (idxA + 1) % size;
            const float frac = readPos - (float) idxA;
            const float delayed = d.memory[idxA] + frac * (d.memory[idxB] - d.memory[idxA]);

            // Feedback with a little high-frequency damping.
            d.feedbackLp += 0.35f * (delayed - d.feedbackLp);
            d.memory[d.writeIndex] = x + params.delayFeedback * d.feedbackLp;

            out[i] = x + delayed * mix;

            if (++d.writeIndex >= size)
                d.writeIndex = 0;
        }
    }
}

void FxProcessor::processReverb (const juce::AudioBuffer<float>& dryIn,
                                 juce::AudioBuffer<float>& buffer, int numSamples)
{
    if (params.reverbMix <= 0.0001f || params.reverbLevel <= 0.0001f)
        return;

    const int n = juce::jmin (numChannels, juce::jmin (dryIn.getNumChannels(), buffer.getNumChannels()));
    const float combGain   = 0.70f + 0.28f * params.reverbRoom;   // 0.70 .. 0.98
    const float allpassGain = 0.75f * params.reverbDiff;          // 0 .. 0.75
    // Room normalisation: the comb network's DC gain is ~4 / (1 - combGain),
    // so scaling by (1 - combGain) keeps the wet level bounded as the room
    // (decay length) grows instead of blowing up near oscillation. The 2.5
    // constant is calibrated (standalone replication of this network): at
    // room 0.5 it puts the note-off ring ~ +6 dB above the dry and the tail
    // ~ -6 dB one second in, so the reverb is clearly audible even at modest
    // dry/wet settings. The wet is intentionally NOT clipped here: any
    // soft-clip knee far below the signal level pins the wet at a constant
    // flat value (the early tail stops audibly decaying, which reads as a
    // "reverb slowly kicking in" plateau) and makes 100% wet sound quiet
    // next to a hot dry signal.
    const float wetScale = 2.5f * (1.0f - combGain);
    const float mix = params.reverbMix;

    for (int ch = 0; ch < n; ++ch)
    {
        auto& r = reverbs[ch];
        const float* in = dryIn.getReadPointer (ch);
        auto* out = buffer.getWritePointer (ch);

        for (int i = 0; i < numSamples; ++i)
        {
            const float x = in[i];

            float combSum = 0.0f;
            for (int c = 0; c < 4; ++c)
            {
                auto& buf = r.combs[c];
                const int size = (int) buf.size();
                int& pos = r.combIndex[c];
                const float delayed = buf[pos];
                buf[pos] = x + combGain * delayed;
                combSum += delayed;
                if (++pos >= size)
                    pos = 0;
            }

            float wet = combSum * wetScale * params.reverbLevel;

            for (int a = 0; a < 2; ++a)
            {
                auto& buf = r.allpasses[a];
                const int size = (int) buf.size();
                int& pos = r.allpassIndex[a];
                const float delayed = buf[pos];
                const float outAp = -allpassGain * wet + delayed;
                buf[pos] = wet + allpassGain * delayed;
                wet = outAp;
                if (++pos >= size)
                    pos = 0;
            }

            out[i] += wet * mix;
        }
    }
}

} // namespace monostep