🎹 Hammond B3 — a tonewheel organ in Rust

A virtual Hammond B3 organ with drawbars, a Leslie rotary speaker, percussion, vibrato/chorus and tube overdrive — written in pure Rust, playable natively and in your browser via WebAssembly.

▶️ Play the live demo — no install, runs in your browser

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✨ Features

• 🎚️ Nine drawbars (16' 5⅓' 8' 4' 2⅔' 2' 1⅗' 1⅓' 1') with authentic tonewheel foldback
• 🌀 Leslie rotary speaker — independent horn & drum rotors, Doppler pitch shift, amplitude swell, stereo micing, and inertial slow / fast / brake ramps
• 🥁 Percussion — single-triggered 2nd / 3rd harmonic, soft / normal, fast / slow decay
• 〰️ Vibrato / Chorus scanner — the classic V1–V3 / C1–C3 selector
• 🎛️ Tube overdrive with a musical soft-limiter on the output
• 🔑 Key click and tonewheel leakage for that vintage grit
• 💾 Presets in human-editable TOML (four factory patches included)
• 🎹 MIDI input (desktop) + an on-screen / computer-keyboard so the web demo needs no hardware
• 🦀 One pure-Rust DSP engine shared by the native app and the WebAssembly build

🏛️ The look

A skeuomorphic wood-and-brass cabinet inspired by the classic B3 console: coloured drawbars, tab switches, a Leslie control and a playable manual — rendered with egui.

🚀 Quick start

Desktop (native audio + MIDI)

cargo run --release

Plug in a MIDI controller (auto-connects to the first port) or play with your computer keyboard.

Web demo (WebAssembly)

cargo install trunk
rustup target add wasm32-unknown-unknown
trunk serve            # open http://127.0.0.1:8080

Every push to main also auto-deploys the demo to GitHub Pages via .github/workflows/pages.yml.

🔈 Web audio notes. Browsers keep audio muted until you interact — so the demo starts its audio engine on your first key press / click. On the web the audio callback shares the browser's main thread, so the engine uses a shared sine wavetable and the UI repaints at a capped ~30 fps to keep the sound smooth. If you ever hear crackling, close other heavy tabs — desktop (cargo run) always has the lowest, cleanest latency.

🎮 Controls

Action	How
Play notes	On-screen keyboard, computer keys A W S E D F T G Y H U J K, or MIDI
Change octave	Octave −/+ buttons
Drawbars	Drag each bar up/down (0–8)
Leslie	Brake / Slow / Fast
Percussion	On, 2nd/3rd, Fast/Slow
Vibrato/Chorus	OFF · V-1 · V-2 · V-3 · C-1 · C-2 · C-3
Presets	Pick + Load, or name + Save

🎼 Presets

Factory presets live in presets/ as editable TOML:

name = "Full Jazz"
drawbars = [8, 8, 8, 0, 0, 0, 0, 0, 0]
vibrato = "c3"
leslie = "slow"
overdrive = 0.1
volume = 0.8

[percussion]
on = true
soft = false
fast = true
third = true

Regenerate them from code with cargo run --example export_presets --no-default-features.

🧱 Architecture

tonewheels × drawbars ─┐
percussion ────────────┤→ vibrato/chorus → overdrive → Leslie → soft-limit → stereo out
key click + leakage ───┘

Module	Responsibility
engine	Free-running tonewheel bank, drawbars, voices, percussion, key click, vibrato, overdrive
leslie	Two-rotor rotary-speaker simulation
preset	Patch data model + TOML (de)serialization + factory presets
params	Lock-free-ish state shared between UI/MIDI and the real-time audio thread
audio	[cpal] output stream (native + WebAudio)
midi	[midir] MIDI input (desktop)
app	[egui]/[eframe] GUI + on-screen keyboard

The audio callback never allocates or blocks: it tries to read the latest patch and drains a small event queue each block.

🧪 Development

cargo test --no-default-features        # fast engine tests (no system deps)
cargo clippy --all-targets -- -D warnings
cargo fmt --all

📜 License

MIT © gpasquero

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Topics: rust · hammond · hammond-b3 · organ · tonewheel · synthesizer · synth · virtual-instrument · leslie · rotary-speaker · drawbars · audio · dsp · audio-synthesis · music · midi · webassembly · wasm · egui · cpal · real-time-audio · vst-alternative · music-production

Built with 🦀 Rust, 🎚️ cpal, 🎹 midir and 🖼️ egui.