SplitBit-Emulator/Source/Emulator/sound.c

// sound.c
// The Voyager's sound device.
// Written by Anachronaut

#include "sound.h"
#include "synth.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <math.h>

// A megahertz, matching the machine. Kept here rather than reaching for machine.h, which
// would drag the whole front end into a device.
#define SOUND_CYCLE_RATE 1000000

static Synth synth;
static uint8_t channel;
static uint8_t parameter;

// Where the machine's clock was when the device started, and how many samples have been made
// since. The next sample is due at start + count * rate / samples, worked out in whole
// numbers each time rather than by adding an approximation over and over - twenty and five
// sixths does not add up to anything exact, and a drift of one part in a thousand is four
// seconds an hour.
static unsigned long startedAt;
static unsigned long samplesMade;

// ---- What has been made and not yet played ----
//
// A ring, written by the machine and read by whatever is playing it. One writer and one
// reader, which is the only sharing that needs no lock at all.
//
// IT DROPS WHEN IT IS FULL, and full means nobody is listening: a headless run makes
// forty-eight thousand samples a second of emulated time and there is nothing to take them.
// Dropping is right there. What must not drop is the COUNT, because that is the clock.
#define SOUND_RING 16384
static int16_t ring[SOUND_RING];
static int ringHead, ringTail;

// And a copy of everything, for --sound. Only kept when a file was asked for, because a long
// run makes millions of samples and a machine that hoarded them by default would be a machine
// that ran out of memory for no reason anybody asked for.
static int16_t *keeping = NULL;
static size_t keptCount, keptRoom;

void soundReset(void) {
    synthInit(&synth, (float)SOUND_SAMPLE_RATE);

    // ---- The device's own power-on state ----
    //
    // synthInit leaves soundThing's defaults, which are a patch EDITOR's: one voice set up to
    // be heard and seven silent behind it, waiting for the edited patch to be copied over
    // them. That is right for a program with one instrument on screen and wrong for a device
    // whose four channels are four independent things.
    //
    // Two consequences if it were left alone, both of which the tests caught. Channels 1 to 3
    // would be silent whatever gain was written to them, because their oscillators are not
    // switched on. And channel 0's first oscillator would arrive at full gain while every
    // other one arrived at nothing - an asymmetry with no reason a programmer could work out.
    //
    // So: EVERY CHANNEL ARRIVES ABLE TO MAKE A SOUND. Oscillator 0 on, at full gain;
    // oscillator 1 off, because two oscillators is a choice and one is the plain case. A
    // program that writes a note number hears that note, which is the shortest useful thing
    // this device can be asked to do.
    for (int i = 0; i < SOUND_CHANNELS; i++) {
        synth.voices[i].oscillators[0].active = 1;
        synth.voices[i].oscillators[0].gain = OSC_MAX_GAIN;
        // Off rather than on-and-silent, because the two oscillators are AVERAGED and not
        // added: a second one that is switched on halves the first whatever its gain is.
        // "Active" is structural, and there is no setting of it that costs nothing.
        synth.voices[i].oscillators[1].active = 0;
        synth.voices[i].oscillators[1].gain = 0.0f;
    }

    channel = 0;
    parameter = 0;
    startedAt = 0;
    samplesMade = 0;
    ringHead = 0;
    ringTail = 0;
    keptCount = 0;
}

void soundKeepSamples(void) {
    keptRoom = 1 << 16;
    keeping = malloc(keptRoom * sizeof(*keeping));
    keptCount = 0;
}

static void pushSample(int16_t sample) {
    const int next = (ringTail + 1) % SOUND_RING;
    if (next != ringHead) {
        ring[ringTail] = sample;
        ringTail = next;
    }
    if (keeping != NULL) {
        if (keptCount == keptRoom) {
            size_t bigger = keptRoom * 2;
            int16_t *grown = realloc(keeping, bigger * sizeof(*keeping));
            if (grown == NULL) {
                return;
            }
            keeping = grown;
            keptRoom = bigger;
        }
        keeping[keptCount++] = sample;
    }
}

void soundTick(unsigned long now) {
    if (startedAt == 0 && samplesMade == 0) {
        startedAt = now;
    }
    for (;;) {
        // When the next one is due, in whole numbers: no accumulated fraction to drift.
        // Sample n is due n periods after the device started, so sample nought is due the
        // moment it starts. Making the first one a period late would put every sample after
        // it a period late too, which is a whole sample of lag for nothing.
        const unsigned long due = startedAt
            + (unsigned long)(samplesMade * (uint64_t)SOUND_CYCLE_RATE
                              / SOUND_SAMPLE_RATE);
        if (now < due) {
            return;
        }
        int16_t sample;
        synthFillBuffer(&synth, &sample, 1);
        pushSample(sample);
        samplesMade++;
    }
}

// ---- A byte, and what it means ----
//
// Everything on this machine is a byte, and a synthesizer wants seconds, hertz and ratios. So
// each parameter says how its 0 to 255 becomes what the engine needs, and the shapes are
// chosen for where the USEFUL part of the range is rather than for arithmetic convenience.
//
// Times are squared, because the difference between five and fifty milliseconds is the whole
// character of a percussive sound and the difference between three and four seconds is
// nothing anybody can hear. Cutoff is exponential for the same reason: pitch is logarithmic
// and so is where a filter sounds like it is.
static float overRange(uint8_t value, float lowest, float highest) {
    return lowest + (highest - lowest) * ((float)value / 255.0f);
}

static float squared(uint8_t value, float highest) {
    const float part = (float)value / 255.0f;
    return part * part * highest;
}

static float exponential(uint8_t value, float lowest, float highest) {
    const float part = (float)value / 255.0f;
    return lowest * powf(highest / lowest, part);
}

// Centred on 128, so that half of nothing is no change and either side of it is a direction.
static float signedRange(uint8_t value, float reach) {
    return ((float)value - 128.0f) / 128.0f * reach;
}

static ModSource sourceFor(uint8_t value) {
    return (value <= MOD_SOURCE_LFO2) ? (ModSource)value : MOD_SOURCE_NONE;
}

static void setOscillator(Oscillator *o, uint8_t which, uint8_t value) {
    switch (which) {
        case SP_OSC_WAVE:   o->waveform = (Waveform)(value % WAVE_COUNT); break;
        case SP_OSC_GAIN:   o->gain = overRange(value, 0.0f, OSC_MAX_GAIN); break;
        case SP_OSC_DUTY:   o->dutyCycle = overRange(value, 0.05f, 0.95f); break;
        // An octave either way, so a step of the byte is 1200/128, about nine cents. Fine
        // enough for the shimmer of two oscillators just apart, which is what detune is
        // mostly for, and wide enough to transpose one of them a whole octave.
        case SP_OSC_DETUNE: o->detune = signedRange(value, 1200.0f); break;
        case SP_OSC_OCTAVE: o->octave = (int)value - 128 < -2 ? -2
                                      : ((int)value - 128 > 2 ? 2 : (int)value - 128); break;
        case SP_OSC_ACTIVE: o->active = value != 0; break;
        case SP_OSC_PWM_SRC:    o->modRouting[0] = sourceFor(value); break;
        case SP_OSC_PWM_DEPTH:  o->modDepth[0] = signedRange(value, 0.5f); break;
        case SP_OSC_DET_SRC:    o->modRouting[1] = sourceFor(value); break;
        case SP_OSC_DET_DEPTH:  o->modDepth[1] = signedRange(value, 1200.0f); break;
        case SP_OSC_GAIN_SRC:   o->modRouting[2] = sourceFor(value); break;
        case SP_OSC_GAIN_DEPTH: o->modDepth[2] = signedRange(value, OSC_MAX_GAIN); break;
        default: break;
    }
}

static void setEnvelope(Envelope *e, uint8_t which, uint8_t value) {
    switch (which) {
        case SP_ENV_ATTACK:  e->attackSec = squared(value, 4.0f); break;
        case SP_ENV_DECAY:   e->decaySec = squared(value, 4.0f); break;
        case SP_ENV_SUSTAIN: e->sustainLevel = overRange(value, 0.0f, 1.0f); break;
        case SP_ENV_RELEASE: e->releaseSec = squared(value, 4.0f); break;
        default: break;
    }
}

static void setFilter(Filter *f, uint8_t which, uint8_t value) {
    switch (which) {
        case SP_FILTER_ACTIVE: f->active = value != 0; break;
        case SP_FILTER_TYPE:   f->type = (FilterType)(value % FILTER_COUNT); break;
        case SP_FILTER_CUTOFF: f->cutoff = exponential(value, 20.0f, 20000.0f); break;
        case SP_FILTER_RES:    f->resonance = overRange(value, 0.0f, 0.99f); break;
        case SP_FILTER_CUT_SRC: f->modRouting = sourceFor(value); break;
        case SP_FILTER_CUT_DEP: f->modDepth = signedRange(value, 8000.0f); break;
        case SP_FILTER_RES_SRC: f->resModRouting = sourceFor(value); break;
        case SP_FILTER_RES_DEP: f->resModDepth = signedRange(value, 0.99f); break;
        default: break;
    }
}

static void setLfo(LFO *l, uint8_t which, uint8_t value) {
    switch (which) {
        case SP_LFO_ACTIVE: l->active = value != 0; break;
        case SP_LFO_WAVE:   l->waveform = (Waveform)(value % WAVE_COUNT); break;
        case SP_LFO_RATE:   l->rate = exponential(value, 0.05f, 20.0f); break;
        case SP_LFO_MODE:   l->mode = value ? LFO_RETRIGGER : LFO_FREE; break;
        default: break;
    }
}

static void soundParameter(uint8_t value) {
    Voice *v = &synth.voices[channel];
    const uint8_t group = parameter & 0xF0;
    const uint8_t which = parameter & 0x0F;
    switch (group) {
        case SP_OSC0:   setOscillator(&v->oscillators[0], which, value); break;
        case SP_OSC1:   setOscillator(&v->oscillators[1], which, value); break;
        case SP_AMPENV: setEnvelope(&v->ampEnv, which, value); break;
        case SP_MODENV: setEnvelope(&v->modEnv, which, value); break;
        case SP_FILTER: setFilter(&v->filter, parameter, value); break;
        case SP_LEVEL_SOURCE:
            // Two settings share a group, because both are about the voice as a whole rather
            // than about one of its parts.
            if (parameter == SP_LEVEL_SOURCE) {
                v->levelSource = sourceFor(value);
            } else if (parameter == SP_VOICE_GATE) {
                v->gate = value ? VOICE_TRIGGER : VOICE_GATE;
            }
        break;
        // ---- The LFOs belong to the channel ----
        //
        // They used to belong to the device, so whichever channel was selected made no
        // difference: two channels playing two different sounds shared one pair of LFOs, and
        // whichever loaded its settings last owned them for both. A sound with its LFO
        // switched off silenced the trill under a sound that was still playing.
        //
        // Four channels are four independent things, which is the rule the rest of this
        // device already followed. So these read the selected channel like every parameter
        // above them, and an LFO written to one channel is inaudible on the other three.
        case SP_LFO0: setLfo(&v->lfos[0], which, value); break;
        case SP_LFO1: setLfo(&v->lfos[1], which, value); break;
        default:
            // A parameter number nothing answers to does nothing. A sound device is a poor
            // place to stop the machine, the same as a screen.
        break;
    }
}

uint8_t soundWrite(uint8_t value, uint8_t port) {
    switch (port) {
        case SOUND_CHANNEL:   channel = value % SOUND_CHANNELS; break;
        case SOUND_PARAMETER: parameter = value; break;
        case SOUND_VALUE:     soundParameter(value); break;
        case SOUND_NOTE:      synthChannelOn(&synth, channel, value); break;
        case SOUND_GATE:
            if (value) {
                synthChannelOn(&synth, channel, synth.voices[channel].midiNote);
            } else {
                synthChannelOff(&synth, channel);
            }
        break;
        case SOUND_VOLUME:    synth.volume = overRange(value, 0.0f, 1.0f); break;
        default: break;
    }
    return 0;
}

uint8_t soundRead(uint8_t port) {
    switch (port) {
        case SOUND_STATUS: {
            uint8_t status = 0;
            for (int i = 0; i < SOUND_CHANNELS; i++) {
                if (synth.voices[i].active) {
                    status |= SOUND_STATUS_SOUNDING;
                }
            }
            return status;
        }
        case SOUND_CHANNEL:   return channel;
        case SOUND_PARAMETER: return parameter;
        case SOUND_NOTE:      return (uint8_t)synth.voices[channel].midiNote;
        default:              return 0;
    }
}

int soundTake(int16_t *into, int wanted) {
    int taken = 0;
    while (taken < wanted && ringHead != ringTail) {
        into[taken++] = ring[ringHead];
        ringHead = (ringHead + 1) % SOUND_RING;
    }
    return taken;
}

int soundWriteSamples(const char *path) {
    // Nothing was kept, which happens if the file was asked for after the machine ran. An
    // empty file is the honest answer: the run made no sound anybody asked to hear.
    if (keeping == NULL) {
        keptCount = 0;
    }
    FILE *file = fopen(path, "wb");
    if (file == NULL) {
        fprintf(stderr, "Error: Couldn't write the sound to: %s\n", path);
        return 1;
    }
    const size_t written = keptCount == 0
        ? 0 : fwrite(keeping, sizeof(*keeping), keptCount, file);
    fclose(file);
    if (written != keptCount) {
        fprintf(stderr, "Error: The sound was not written whole to: %s\n", path);
        return 1;
    }
    return 0;
}