peacock/plugin/ic29.cpp

/*
   Peacock-8 VA polysynth

   Copyright 2024 Gordon JC Pearce <gordonjcp@gjcp.net>

   Permission to use, copy, modify, and/or distribute this software for any
   purpose with or without fee is hereby granted, provided that the above
   copyright notice and this permission notice appear in all copies.

   THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
   WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
   MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
   SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
   WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
   OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
   CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/

#include "ic29.hpp"

#include "ic29tables.hpp"

Synth ic29;

Synth::Synth() {
    d_debug("initialising synth\n");
    envAtk = 0x00;
    envDcy = 0x50;
    envStn = 0x7f;
    envRls = 0x3f;
    portaCoeff = 0x0;
    lfo.speed = 0x1f;
}

void Synth::buildTables(double sampleRate) {
    for (uint8_t i = 0; i < 104; i++) {
        // slightly flat middle C from ROM divider table
        // actually adjusted a little so that the notes are bang on
        // on the real synth the tuning knob is tweaked a little off to pull it in
        pitchTable[i] = 260.15f * powf(2, (i - 36) / 12.0f) / sampleRate;
    }
}

void Synth::run() {
    // handle a "loop" worth of envelopes, pitch calculations, etc
    // callled once every 4.3ms block of samples

    ic29.lfo.run();

    masterPitch = 0x1818;

    for (uint8_t i = 0; i < NUM_VOICES; i++) {
        ic29.voices[i].update();
    }
}

void Synth::voiceOn(uint8_t voice, uint8_t note) {
    // enable synth voice, start it all running
    voice &= 0x7f;
    ic29.voices[voice].on(note);
}

void Synth::voiceOff(uint8_t voice) {
    // enable synth voice, start it all running
    voice &= 0x7f;
    ic29.voices[voice].off();
}

LFO::LFO() {
    lfoOut = 0;
    phase = 0;

    // phase is where we are in the LFO delay cycle
    // the delay envelope sets the depth of pitch and VCF modulation
    // running normally the amplitude is maxed out, and when the first
    // key is struck the holdoff timer and envelope will be reset to zero
    delayPhase = LFO_RUN;
}

void LFO::run() {
    // slightly different from the real synth code which does not use signed
    // variables, since the CPU doesn't support them

    lfoOut += phase ? lfoRateTable[speed] : -lfoRateTable[speed];
    if (lfoOut > 0x1fff) {
        lfoOut = 0x1fff;
        phase = 0;
    }
    if (lfoOut < -0x1fff) {
        lfoOut = -0x1fff;
        phase = 1;
    }

    //printf("lfoOut=%04x\n", lfoOut);
}

Envelope::Envelope() {
    level = 0;
    phase = ENV_IDLE;
}

void Envelope::run() {
    uint16_t tempStn = ic29.envStn << 7;
    switch (phase) {
        case ENV_ATK:
            level += atkTable[ic29.envAtk];
            if (level > 0x3fff) {
                level = 0x3fff;
                phase = ENV_DCY;
            }
            break;
        case ENV_DCY:
            if (level > tempStn) {
                level = (((level - tempStn) * dcyTable[ic29.envDcy]) >> 16) + tempStn;
            } else {
                level = tempStn;
            }
            break;
        case ENV_RLS:
            level = (level * dcyTable[ic29.envRls]) >> 16;
            break;
        case ENV_IDLE:
        default:
            break;
    }
}

Voice::Voice() {
    subosc = .11;
}

void Voice::calcPitch() {
    uint16_t target = note << 8;

    // Portamento is a linear change of pitch - it'll take twice as long
    // to jump two octaves as it takes to jump one
    // By comparison "glide" is like an RC filter, for example in the TB303
    // This is implemented here by adding on a step value until you pass
    // the desired final pitch. Once that happens the value is clamped to the
    // desired pitch.

    if (ic29.portaCoeff != 0) {
        // portamento up
        if (pitch < target) {
            pitch += ic29.portaCoeff;
            if (pitch > target) pitch = target;
        }
        // portamento down
        if (pitch > target) {
            pitch -= ic29.portaCoeff;
            if (pitch < target) pitch = target;
        }
    } else {
        pitch = target;
    }

    pitch += ic29.masterPitch;

    if (pitch < 0x3000) pitch = 0x3000;  // lowest note
    if (pitch > 0x9700) pitch = 0x6700;  // highest note

    pitch -= 0x3000;

    // interpolate between the two table values
    double o1 = ic29.pitchTable[pitch >> 8];
    double o2 = ic29.pitchTable[(pitch >> 8) + 1];
    double frac = (pitch & 0xff) / 256.0f;

    omega = ((o2 - o1) * frac) + o1;
}

void Voice::update() {
    // calculate the once-per-block values
    env.run();
    calcPitch();
    // do filter values
}

void Voice::on(uint8_t key) {
    voiceState = V_ON;
    note = key;
    env.on();
}

void Voice::off() {
    // sustain - I need to rethink this bit FIXME
    voiceState = V_OFF;
    if (!ic29.sustained) {
        env.off();
    }
}