monostep/Source/dsp/SynthVoice.h

#pragma once

#include <JuceHeader.h>
#include "WaveTables.h"

namespace monostep
{

class SynthVoice
{
public:
    struct Params
    {
        Waveform waveA = Waveform::saw;
        Waveform waveB = Waveform::square;
        float detuneRatio = 1.0f;
        float mix = 0.5f;
        float cutoff = 7000.0f;
        float resonance = 0.15f;
        float attack = 0.005f;
        float decay = 0.3f;
        float sustain = 0.7f;
        float release = 0.4f;
        float glide = 0.12f;
        float master = 0.9f;
    };

    void prepare (double sr)
    {
        sampleRate = (float) sr;
        reset();
    }

    void reset()
    {
        phaseA = phaseB = 0.0f;
        currentFreq = targetFreq = 440.0f;
        smoothing = 0.0f;
        filterLow = filterBand = 0.0f;
        env = 0.0f;
        envStage = Stage::idle;
        gate = false;
    }

    void setParams (const Params& p) { params = p; }

    bool isActive() const { return gate; }

    void noteOn (float freqHz, bool legato)
    {
        targetFreq = freqHz;

        if (gate && legato)
        {
            const float time = std::max (params.glide, 0.001f);
            smoothing = 1.0f - std::exp (-1.0f / (time * sampleRate));
        }
        else
        {
            currentFreq = targetFreq;
            smoothing = 0.0f;
            retriggerEnvelope();
        }

        gate = true;
    }

    void noteOff()
    {
        if (gate)
        {
            gate = false;

            if (envStage != Stage::idle && envStage != Stage::release)
                envStage = Stage::release;
        }
    }

    void render (juce::AudioBuffer<float>& buffer, int numSamples)
    {
        auto* out = buffer.getWritePointer (0);

        for (int i = 0; i < numSamples; ++i)
            out[i] = renderSample();
    }

private:
    enum class Stage { idle, attack, decay, sustain, release };

    void retriggerEnvelope()
    {
        envStage = Stage::attack;
    }

    void updateEnvelope()
    {
        const float sr = sampleRate;

        switch (envStage)
        {
            case Stage::attack:
                env += 1.0f / (params.attack * sr);
                if (env >= 1.0f) { env = 1.0f; envStage = Stage::decay; }
                break;

            case Stage::decay:
                env -= (1.0f - params.sustain) / (params.decay * sr);
                if (env <= params.sustain) { env = params.sustain; envStage = Stage::sustain; }
                break;

            case Stage::sustain:
                env = params.sustain;
                break;

            case Stage::release:
                env -= 1.0f / (params.release * sr);
                if (env <= 0.0f) { env = 0.0f; envStage = Stage::idle; }
                break;

            case Stage::idle:
                break;
        }
    }

    void updateGlide()
    {
        if (smoothing > 0.0f)
        {
            currentFreq += (targetFreq - currentFreq) * smoothing;

            if (std::fabs (targetFreq - currentFreq) < 0.01f)
            {
                currentFreq = targetFreq;
                smoothing = 0.0f;
            }
        }
    }

    float processFilter (float input)
    {
        const float f = 2.0f * std::sin (juce::MathConstants<float>::pi * params.cutoff / sampleRate);
        const float q = 1.0f / (1.0f + params.resonance * 9.0f);

        filterLow += f * filterBand;
        const float high = input - filterLow - q * filterBand;
        filterBand += f * high;

        return filterLow;
    }

    float renderSample()
    {
        updateEnvelope();
        updateGlide();

        const float incA = currentFreq / sampleRate;
        const float incB = (currentFreq * params.detuneRatio) / sampleRate;

        const float a = renderWave (params.waveA, phaseA, incA);
        const float b = renderWave (params.waveB, phaseB, incB);

        phaseA = frac (phaseA + incA);
        phaseB = frac (phaseB + incB);

        float out = (1.0f - params.mix) * a + params.mix * b;

        out = processFilter (out);

        return out * env * params.master;
    }

    float sampleRate = 44100.0f;
    Params params;

    float phaseA = 0.0f;
    float phaseB = 0.0f;
    float currentFreq = 440.0f;
    float targetFreq = 440.0f;
    float smoothing = 0.0f;

    float filterLow = 0.0f;
    float filterBand = 0.0f;

    float env = 0.0f;
    Stage envStage = Stage::idle;
    bool gate = false;
};

} // namespace monostep