synthie

A Rust synthesizer engine library with polyphonic voices, ADSR envelopes, state-variable filters, LFO modulation, and reverb.

Features

• Polyphonic voice engine with configurable channel count
• Five waveforms: Pulse, Sawtooth, Triangle, Noise, Pulse+Saw
• ADSR amplitude envelope with optional reverse (swell/duck) mode
• State-variable filter - Low-pass, Band-pass, and High-pass with cutoff, resonance, and drive
• LFO targeting pitch, pulse width, filter cutoff, or volume
• Reverb FX with room size and damping controls
• Multi-timbral channels via ChannelNo newtypes
• Drum machine beside the voice pools: kick, snare, hi-hats, crash, toms and clap
• Sample-accurate sequencing on any host via Sequencer and SequencedProcessor
• Serde support via the serde feature (enabled by default)

Quick Start

use synthie::audio::engine::setup_audio;
use synthie::params::{AudioEvent, MidiNote};

fn main() -> anyhow::Result<()> {
    let (stream, tx, _scope_rx) = setup_audio()?;
    let _stream = stream; // keep alive

    tx.send(AudioEvent::NoteOn(MidiNote(60)))?;
    std::thread::sleep(std::time::Duration::from_secs(1));
    tx.send(AudioEvent::NoteOff(MidiNote(60)))?;
    Ok(())
}

See examples/ for full usage.

Bring Your Own Audio Backend

SynthProcessor has no I/O and renders into any interleaved f32 buffer, so it can run inside kira, a game engine's stream, or an AudioWorklet. Pair it with a Sequencer for events that land on the exact frame, whatever buffer size the backend uses:

use synthie::prelude::*;

struct FourOnTheFloor;

impl Sequencer for FourOnTheFloor {
    fn tick(&mut self, sample_rate: f32, out: &mut Vec<AudioEvent>) -> usize {
        out.push(AudioEvent::Drum(DrumHit::Kick));
        (sample_rate * 0.5) as usize // 120 bpm
    }
}

let mut synth = SequencedProcessor::new(SynthProcessor::<4>::new(48_000.0), FourOnTheFloor);
let mut buf = vec![0.0; 2 * 512]; // stereo, interleaved
synth.process_block(&[], &mut buf, 2); // call from the audio callback

Already using kira? Enable the kira feature and play the synth as a kira sound instead, mixed, faded and paused like any other:

use synthie::kira::SynthSoundData;
use synthie::pattern::SongPlayer;

let mut synth = manager.play(SynthSoundData::new().with_sequencer(SongPlayer::new(song)))?;
synth.drum(DrumHit::Kick)?;
synth.set_volume(-6.0, Tween::default());

Game Music

synthie::pattern plays tracker-style songs written in a compact notation, sample-accurately through the same Sequencer trait:

use synthie::params::ChannelNo;
use synthie::pattern::{Song, SongPlayer, Tempo};

// One row per eighth note at 152 bpm.
let song = Song::new(Tempo::bpm(152.0, 2))
    .lane(ChannelNo(0), "E4 . G4 . A4 . B4 . | E5 . . . - . . .")?
    .lane(ChannelNo(1), "E2 E2 E2 E2 G2 A2 . . | E2 . . . - . . .")?
    .lane(ChannelNo(3), "k+c h s h k k s h | k h s h k k s o")?;
let player = SongPlayer::new(song); // hand to any host as a Sequencer

Chord cells play several notes from one lane on the lane's channel, e.g. a power chord as E2+B2+E3, or as semitone offsets from the root, E2^07c!. See the synthie::pattern docs for the full notation (notes, chords, holds, note-offs, drum hits, chip arpeggios, patch changes).

Feature Flags

Terminal UI

The synth-tui crate provides a full ratatui-based terminal UI. See the repository root for screenshots.