sm-26/Source/SynthEngine.cpp

#include "SynthEngine.h"
#include <cmath>

namespace sm26 {

SynthEngine::SynthEngine()
{
    auto def = defaultParams();
    for (int i = 0; i < kNumParams; ++i)
        params[i] = def[i];

    knobParams[0] = PCUTOFF;
    knobParams[1] = PRES;
    knobParams[2] = PFENV;
    knobParams[3] = PDMIX;

    knobNames[0] = "CUTOFF";
    knobNames[1] = "RES";
    knobNames[2] = "F-ENV";
    knobNames[3] = "DELAY";

    for (int i = 0; i < kNumKnobs; ++i)
    { knobLows[i] = 0.0f; knobHighs[i] = 1.0f; }

    std::srand (12345);
}

void SynthEngine::prepare (double sr, int mb)
{
    sampleRate = sr;
    maxBlock = mb;
    delay.prepare (sr);
    allNotesOff();
    reset();
}

void SynthEngine::reset()
{
    allNotesOff();
    delay.clear();
}

void SynthEngine::loadPreset (const Preset& p)
{
    for (int i = 0; i < kNumParams; ++i)
        params[i] = p.base[i];
    for (int i = 0; i < kNumKnobs; ++i)
    {
        knobParams[i] = p.ctl[i].param;
        knobNames[i]  = p.ctl[i].name;
        knobLows[i]   = p.ctl[i].lo;
        knobHighs[i]  = p.ctl[i].hi;
    }
    allNotesOff();
}

void SynthEngine::setPresetIndex (int i)
{
    currentPresetIndex = i;
    loadPreset (*PresetStore::findByIndex (i));
}

void SynthEngine::setParam (int id, float n01)
{
    if (id < 0 || id >= kNumParams) return;
    params[id] = juce::jlimit (0.0f, 1.0f, n01);
}

float SynthEngine::getParam (int id) const
{
    if (id < 0 || id >= kNumParams) return 0.0f;
    return params[id];
}

SynthEngine::KnobView SynthEngine::knobView (int knob) const
{
    if (knob < 0 || knob >= kNumKnobs) return {};
    KnobView k;
    k.name  = knobNames[knob];
    k.param = knobParams[knob];
    k.value01 = getParam (k.param);
    return k;
}

float SynthEngine::knobValue (int knob) const
{
    if (knob < 0 || knob >= kNumKnobs) return 0.0f;
    return getParam (knobParams[knob]);
}

const char* SynthEngine::waveNameFor (int index) const
{
    return sm26::waveName (juce::jlimit (0, 4, index));
}

void SynthEngine::noteOn (int note, float vel)
{
    Voice* v = findFreeOrSteal();
    resetVoice (*v, note, vel);
}

void SynthEngine::noteOff (int note)
{
    for (auto& v : voices)
        if (v.active && v.note == note)
            v.envState = 3;
}

void SynthEngine::allNotesOff()
{
    for (auto& v : voices) { v.active = false; v.env = 0.0; v.envState = 0; }
    activeNotes = 0;
}

SynthEngine::Voice* SynthEngine::findFreeOrSteal()
{
    int freeIdx = -1;
    int oldest = -1;
    int oldestAge = -1;
    for (int i = 0; i < kNumVoices; ++i)
    {
        if (! voices[i].active) { freeIdx = i; break; }
        if (voices[i].age > oldestAge) { oldest = i; oldestAge = voices[i].age; }
    }
    if (freeIdx >= 0) { activeNotes++; return &voices[freeIdx]; }
    voices[oldest].envState = 3;
    voices[oldest].env = 0.0f;
    return &voices[oldest];
}

void SynthEngine::resetVoice (Voice& v, int note, float vel)
{
    v.active = true;
    v.note = note;
    v.velocity = vel;
    v.envState = 0;
    v.env = 0.0f;
    v.age = 0;
    v.ic1eq = 0.0;
    v.ic2eq = 0.0;

    double freq = 440.0 * std::pow (2.0, (note - 69) / 12.0);
    double inc = freq / sampleRate;

    double oct1 = paramReal (PO1OCT, params[PO1OCT]);
    double oct2 = paramReal (PO2OCT, params[PO2OCT]);
    double dt1  = paramReal (PO1CT,  params[PO1CT])  / 1200.0;
    double dt2  = paramReal (PO2CT,  params[PO2CT])  / 1200.0;

    double f1 = freq * std::pow (2.0, oct1 + dt1);
    double f2 = freq * std::pow (2.0, oct2 + dt2);

    v.inc1 = f1 / sampleRate;
    v.inc2 = f2 / sampleRate;
    v.glidedInc1 = v.inc1;
    v.ph1 = 0.0;
    v.ph2 = 0.0;
}

float SynthEngine::oscWave (int wave, double phase)
{
    double ph = phase - std::floor(phase);
    switch (wave)
    {
        case 0: return (float) std::sin (ph * 6.283185307179586);
        case 1: return (float) (1.0 - 4.0 * std::fabs (ph - 0.5));
        case 2: return (float) (2.0 * ph - 1.0);
        case 3: return (float) (ph < 0.5 ? 1.0 : -1.0);
        case 4: return (float) (((double) std::rand() / (double) RAND_MAX) * 2.0 - 1.0);
        default: return 0.0f;
    }
}

static float softClip (float x)
{
    return std::tanh (x * 1.5f) / std::tanh(1.5f);
}

double SynthEngine::cutoffFor (const Voice& v, double baseCutoff, double envAmt, double envLevel)
{
    double baseHz = paramReal (PCUTOFF, (float) baseCutoff);
    baseHz = std::clamp (baseHz, 20.0, 20000.0);
    double mod = envAmt * envLevel * 5.0;
    double hz = baseHz * std::pow (2.0, mod);
    hz = std::clamp (hz, 20.0, std::min (sampleRate * 0.45, 20000.0));
    return (float) hz;
}

void SynthEngine::process (AudioBuffer<float>& buffer, MidiBuffer& midi,
                           int n, double bpm, bool transportPlaying)
{
    wasPlaying = transportPlaying;
    lastBpmValue = (bpm > 10.0 && bpm < 300.0) ? bpm : 120.0;

    const float cutN01  = params[PCUTOFF];
    const float resN01  = params[PRES];
    const float fenvN01 = params[PFENV];
    const float ftypeN01= params[PFTYPE];
    const float atkN01  = params[PATK];
    const float decN01  = params[PDEC];
    const float susN01  = params[PSUS];
    const float relN01  = params[PREL];
    const float driveN01= params[PDRIVE];
    const float glideN01= params[PGLIDE];
    const float masterN01= params[PMASTER];
    const float mixN01  = params[PMIX];
    const float noiseN01= params[PNOISE];

    const double atkSec  = paramReal (PATK, atkN01);
    const double decSec  = paramReal (PDEC, decN01);
    const double susLevel = susN01;
    const double relSec  = paramReal (PREL, relN01);

    const double atkCoef = 1.0 - std::exp (-1.0 / (atkSec * sampleRate + 1.0));
    const double decCoef = 1.0 - std::exp (-1.0 / (decSec * sampleRate + 1.0));
    const double relCoef = 1.0 - std::exp (-1.0 / (relSec * sampleRate + 1.0));

    const double drive = 0.1 + driveN01 * 2.4;
    const double glideCoef = glideN01 < 0.001 ? 1.0 : 1.0 - std::exp (-1.0 / (glideN01 * sampleRate + 1.0));
    const double master = masterN01;

    const double fenvScale = fenvN01 * 5.0;
    (void) fenvScale;

    const float gMix   = mixN01;
    const float g1     = 1.0f - gMix;
    const float g2     = gMix;
    const float g1p    = (float) std::sqrt (g1);
    const float g2p    = (float) std::sqrt (g2);

    const int filterType = paramFilterType (ftypeN01);

    bool delaySync = params[PDSYNC] > 0.5f;
    int  stepIdx   = juce::jlimit (0, 15, (int) juce::roundToInt (params[PDSTEPS] * 15.0f));
    float delayMsParam = paramReal (PDTIME, params[PDTIME]);
    float delaySec;
    if (delaySync)
        delaySec = (float) (stepsBeats()[stepIdx] * 60.0 / lastBpmValue);
    else
        delaySec = delayMsParam * 0.001f;
    delaySec = std::clamp (delaySec, 0.001f, 17.0f);
    lastDelaySamples = delaySec * sampleRate;

    const float delayFB = params[PDFB];
    const float delayMix= params[PDMIX];
    const float dryMix  = 1.0f - delayMix;
    const float wetMix  = delayMix;

    int delayWrite = (int) delay.writePos[0];
    int delayRead  = (delayWrite - (int) lastDelaySamples + delay.maxLen * 2) % delay.maxLen;
    (void) delayRead;

    for (const auto& metadata : midi)
    {
        MidiMessage msg = metadata.getMessage();
        int sm = metadata.samplePosition;
        if (sm < n && msg.isNoteOn())
            noteOn (msg.getNoteNumber(), msg.getFloatVelocity());
        else if (sm < n && msg.isNoteOff())
            noteOff (msg.getNoteNumber());
    }

    float* outL = buffer.getWritePointer (0);
    float* outR = buffer.getNumChannels() > 1 ? buffer.getWritePointer (1) : nullptr;

    for (int s = 0; s < n; ++s)
    {
        float sumL = 0.0f, sumR = 0.0f;

        for (auto& v : voices)
        {
            if (! v.active) continue;

            v.age++;
            v.ph1 += v.inc1;
            v.ph2 += v.inc2;
            if (v.ph1 > 1.0) v.ph1 -= 1.0;
            if (v.ph2 > 1.0) v.ph2 -= 1.0;

            v.glidedInc1 = (float) ((1.0 - glideCoef) * v.glidedInc1 + glideCoef * v.inc1);

            switch (v.envState)
            {
                case 0: v.env += (1.0 - v.env) * atkCoef; if (v.env > 0.999) v.envState = 1; break;
                case 1: v.env += (susLevel - v.env) * decCoef; break;
                case 2: break;
                case 3: v.env += (0.0 - v.env) * relCoef; if (v.env < 0.001) { v.active = false; v.env = 0.0; activeNotes--; } break;
            }

            float o1 = oscWave (paramWaveIndex (params[PO1WAVE]), v.ph1);
            float o2 = oscWave (paramWaveIndex (params[PO2WAVE]), v.ph2);

            float raw = g1p * o1 + g2p * o2 + noiseN01 * (float) (((double) std::rand() / (double) RAND_MAX) * 2.0 - 1.0) * 0.5f;
            raw *= 0.7f;

            float cutoffHz = cutoffFor (v, cutN01, fenvN01, v.env);
            float Q = 0.5f + resN01 * 14.0f;
            float k = 1.0f / Q;
            double f = cutoffHz / (float) sampleRate;
            if (f > 0.49) f = 0.49;
            double g = std::tan (juce::MathConstants<double>::pi * f);
            double a1 = 1.0 / (1.0 + g * (g + k));
            double a2 = g * a1;
            double a3 = g * a2;

            double vin = raw;
            double v3 = vin - v.ic2eq;
            double v1 = a1 * v.ic1eq + a2 * v3;
            double v2 = v.ic2eq + a2 * v.ic1eq + a3 * v3;
            v.ic1eq = 2.0 * v1 - v.ic1eq;
            v.ic2eq = 2.0 * v2 - v.ic2eq;

            float filtered;
            switch (filterType)
            {
                case 0:  filtered = (float) v2; break;
                case 1:  filtered = (float) v1; break;
                case 2:  filtered = (float) (vin - k * v1 - v2); break;
                default: filtered = (float) v2; break;
            }

            float sig = softClip (filtered * (float) drive);
            sig *= (float) (v.env * v.velocity * master);
            sumL += sig;
            sumR += sig;
        }

        float dry = sumL;
        int w = delay.writePos[0];
        float delayed = delay.buf[0][w];
        float fb = dry + delayed * (float) delayFB;
        fb = softClip (fb * 0.7f);
        delay.buf[0][w] = fb;
        delay.buf[1][w] = fb;
        delay.writePos[0] = (w + 1) % delay.maxLen;
        delay.writePos[1] = (w + 1) % delay.maxLen;

        outL[s] = dryMix * dry + wetMix * delayed;
        if (outR) outR[s] = outL[s];
    }
}

} // namespace sm26