SplitBit-Emulator/Source/Emulator/synth.h

// synth.h
// The Voyager's sound, vendored from soundThing.
//
// ---- Where this came from ----
//
// soundThing is a polyphonic subtractive synthesizer written by Anachronaut, and lives in its
// own repository. What is here is its VOICE ENGINE and nothing else: synth.c pulls in maths,
// stdlib, stdint and stdio and knows nothing about Raylib, MIDI, patches or the user
// interface, which is what made it liftable at all.
//
// It is copied rather than submoduled. Two files against tying this build to another
// repository's history is not a close call, and what a copy costs is that changes have to be
// carried across on purpose - in BOTH directions, which has now happened once each way.
//
// ---- What was changed ----
//
// Nothing. This is soundThing's engine at b73e5c0, character for character, except that
// em-dashes and arrows in its comments are written as ASCII here because this tree is ASCII
// only. That rule is local and is not an improvement, so it was not sent upstream.
//
// It did not start that way. Three changes were made here first - a routed voice level, a
// seeded noise generator, and channels asked for by number - and all three went up. What came
// back was those three plus what they made possible: a voice that can end itself rather than
// waiting for a key, and a triggered voice that re-arms its oscillators so a one-shot is the
// same one-shot twice. A game is nearly all one-shots, which is why the traffic went that way.
//
// So the thing to keep current is no longer a list. It is this: if either copy changes, the
// other one has to be told.
//
// Written by Anachronaut

#ifndef SYNTH_H
#define SYNTH_H

#include <stdint.h>

#define VOICE_COUNT 8
#define OSC_COUNT 2
#define LFO_COUNT 2
#define OSC_MAX_GAIN 4.0f

typedef enum {
    WAVE_SINE,
    WAVE_TRIANGLE,
    WAVE_SAW,
    WAVE_RAMP,
    WAVE_PULSE,
    WAVE_NOISE,
    WAVE_COUNT  // handy for the modulo wrap on waveform switching
} Waveform;

// Envelope structures:
typedef enum {
    ENV_IDLE,
    ENV_ATTACK,
    ENV_DECAY,
    ENV_SUSTAIN,
    ENV_RELEASE
} EnvStage;

typedef enum {
    MOD_SOURCE_NONE    = 0,
    MOD_SOURCE_AMP_ENV = 1,
    MOD_SOURCE_MOD_ENV = 2,
    MOD_SOURCE_LFO     = 3,
    MOD_SOURCE_LFO2    = 4
} ModSource;

// ---- Whether the key holds the note up ----
//
// Gated is what a keyboard wants: the sound lasts as long as the finger does, and lifting it
// starts the release. Triggered is what a drum wants - the note is struck and then plays its
// own length, and the key coming up is not its business. Sustain and release have no meaning
// in a triggered voice, because both of them are answers to a question about the key.
typedef enum {
    VOICE_GATE    = 0,
    VOICE_TRIGGER = 1
} VoiceGate;

typedef struct {
    EnvStage stage;
    float    value;      // current output value, 0.0 to 1.0
    float    attackSec;
    float    decaySec;
    float    sustainLevel;
    float    releaseSec;
    // Set from the voice's gate at note-on, not read from it live, so that flipping the
    // switch under a sounding note cannot strand it half-way through a shape it was not
    // started in. One-shot runs the decay to nothing and finishes there.
    int      oneShot;
} Envelope;

// ---- Where an LFO is in its cycle ----
//
// Split out of the LFO itself because there is now more than one answer at a time. A free
// LFO has one cycle that every voice reads, which is what makes it a single sweep across a
// chord. A retriggered one has a cycle PER VOICE, restarted when that voice is struck - and
// a voice resetting the shared one would drag every note already sounding along with it.
typedef struct {
    float    phase;
    float    noiseHeld;
    float    noisePhase;
    // Its own noise, seeded at init. rand() is global state shared with the whole process and
    // varies between C libraries, so the same patch sounded different on different machines
    // and no recorded result could mean anything. One generator EACH rather than one shared,
    // because two noise sources drawing from the same stream are not two noise sources.
    uint32_t noiseState;
} LfoState;

// ---- Whether an LFO keeps its own time or starts when struck ----
//
// Free is one cycle running under everything, which is what vibrato across a held chord
// wants. Retriggered starts at the beginning of its shape every time a voice begins, which
// is the only way a one-shot sounds the same twice - a free LFO is wherever the wall clock
// left it, so the same drum caught at a different moment is a different drum.
typedef enum {
    LFO_FREE      = 0,
    LFO_RETRIGGER = 1
} LfoMode;

typedef struct {
    LfoState run;         // the free-running cycle, read by every voice in LFO_FREE
    float    rate;        // Hz
    Waveform waveform;
    int      active;
    LfoMode  mode;
} LFO;

typedef enum {
    FILTER_LOWPASS,
    FILTER_HIGHPASS,
    FILTER_BANDPASS,
    FILTER_COUNT
} FilterType;

typedef struct {
    float      cutoff;      // Hz
    float      resonance;   // 0.0 (flat) to 0.99 (near self-oscillation)
    FilterType type;
    int        active;
    float      low, band;   // TPT integrator states s1, s2
    int        modRouting;
    float      modDepth;    // Hz
    int        resModRouting;
    float      resModDepth; // resonance units (-0.99..0.99)
} Filter;

typedef struct {
    float    phase;
    float    dutyCycle;
    Waveform waveform;
    float    detune;      // cents, 0 = no detune
    float    noiseHeld;   // last drawn random value for clocked noise
    float    noisePhase;  // tracks when to draw a new noise value
    // Its own noise, seeded at init. rand() is global state shared with the whole process and
    // varies between C libraries, so the same patch sounded different on different machines
    // and no recorded result could mean anything. One generator EACH rather than one shared,
    // because two noise sources drawing from the same stream are not two noise sources.
    uint32_t noiseState;
    float    gain;
    int      active;          // whether this oscillator contributes to output
    int      octave;          // transposition in octaves, -2 to +2
    // Modulation routing: one source per destination by design.
    // Each parameter (pwm, detune, gain) has exactly one mod source and one depth.
    int      modRouting[3];   // 0=off, 1=env0, 2=env1, 3=lfo0, 4=lfo1
    float    modDepth[3];     // Depth of modulation parameter
} Oscillator;

typedef struct {
    Oscillator oscillators[OSC_COUNT];
    float      freqHz;
    int        active;
    int        midiNote;
    Envelope   ampEnv;
    Envelope   modEnv;
    Filter     filter;
    // ---- What shapes how loud this voice is ----
    //
    // Envelope 0 used to, always, with no way to say otherwise - so routing it to a filter or
    // an oscillator meant it shaped the volume too, whether that was wanted or not. Every
    // other destination here names its source; this one does now as well.
    //
    // NOT the base-and-depth pair the others use, because a level is not a deviation from a
    // resting value - it is a shape from nothing to full, and multiplying is what an amplitude
    // envelope does. So this names a source outright, and MOD_SOURCE_NONE means the voice is
    // simply at full and whatever env0 is doing is somebody else's business.
    //
    // It also makes two things possible that were not: envelope 1 shaping the volume, and an
    // LFO doing it, which is tremolo.
    ModSource  levelSource;
    // ---- Whether the key holds this voice up ----
    //
    // The other half of what envelope 0 used to decide on its own. Naming the level's source
    // said what shapes the sound; this says who ends it. Without it a voice can only ever
    // finish because a key came up, which is no use to a drum.
    VoiceGate  gate;
    // One cycle per LFO per voice, used only by the LFOs set to LFO_RETRIGGER. Runtime state
    // like the envelope stages and the filter's integrators, so synthSyncVoices leaves it
    // alone - it is where this voice is, not what the patch says.
    LfoState   lfoRun[LFO_COUNT];
} Voice;

typedef struct {
    float    sampleRate;
    float    pitchBend;
    float    pitchBendRange;
    int      lastStolenVoice;
    Voice    voices[VOICE_COUNT];
    float    volume;  // 0.0 to 1.0, master output level
    LFO      lfos[LFO_COUNT];
} Synth;

// Envelope functions:
void  envelopeInit(Envelope *e, float attackSec, float decaySec, float sustainLevel, float releaseSec);
void  envelopeNoteOn(Envelope *e);
void  envelopeNoteOff(Envelope *e);
float envelopeTick(Envelope *e, float sampleRate);

// Oscillator functions:
void oscillatorInit(Oscillator *o, Waveform waveform, float dutyCycle, float detune, float gain);
float oscillatorTick(Oscillator *o, float freqHz, float bendMultiplier, float sampleRate,
                     float dutyCycle, float detune, float gain);

// Synth functions:
void  synthInit(Synth *s, float sampleRate);
void  synthResetPatch(Synth *s);
void  synthNoteOn(Synth *s, int midiNote);
void  synthNoteOff(Synth *s, int midiNote);

// ---- A channel asked for by number ----
//
// The two above hunt for a free voice and steal round-robin, which is what a keyboard wants:
// a player presses keys and does not care which voice sounds them. Something driving this as
// HARDWARE does care - channel two is channel two, it keeps its patch between notes, and
// nothing may take it away. Both ways of asking are here and neither changes the other.
void  synthChannelOn(Synth *s, int channel, int midiNote);
void  synthChannelOff(Synth *s, int channel);
void  synthFillBuffer(Synth *s, int16_t *out, int frames);
void  synthSyncVoices(Synth *s);

// LFO functions:
float lfoTick(LFO *l, float sampleRate);
// The same advance against a cycle that is not the LFO's own, so a voice can run its own.
float lfoTickState(const LFO *l, LfoState *st, float sampleRate);

// Filter functions:
float filterTick(Filter *f, float input, float cutoff, float resonance, float sampleRate);
const char *filterTypeName(FilterType t);

// Waveform functions:
float waveformSample(Waveform w, float phase, float dutyCycle, float noiseHeld);
const char *waveformName(Waveform w);

#endif