🎛️ Rusted Moog

A real-time, glitch-free virtual analog synthesizer — written from scratch in Rust.

A Minimoog-inspired 3-oscillator polysynth with a Moog ladder filter, born from a Python synth that couldn't stop clicking.

🎹 Play the real synth in your browser (WebAssembly) →

(The actual Rust + egui app compiled to WASM — same panel, same knobs, same sound. No install.)

⚠️ In the browser, audio can crackle or lag a little — WebAssembly schedules audio on the main thread. The native desktop build runs flawlessly (audio on its own real-time thread). See Build & run.

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Why does this exist?

It started as VOOG, a synth written in Python + NumPy. It sounded great — until you played a chord. Then it clicked, popped, and dropped out. The culprit wasn't CPU power; it was garbage-collection pauses and GIL contention firing inside the audio callback, blowing the 5.8 ms real-time deadline at random.

You can't fix that with faster Python. So we rewrote the whole thing in Rust:

No garbage collector. No locks in the audio thread. No allocations in the hot path. No glitches.

Same synth architecture, deterministic real-time audio, and a GUI that actually looks like hardware.

✨ Features

• 🎚️ 3 oscillators — sine / saw / square / triangle, band-limited wavetables, per-osc octave, semitone, detune & level
• 🔊 Moog ladder filter — authentic Huovilainen 24 dB/oct model with resonance, envelope & key-tracking
• 📈 Dual ADSR envelopes — independent amp & filter contours
• 🌊 LFO — 4 waveforms, routable to filter / pitch / amp
• 🎹 Jupiter-8-style arpeggiator — Up / Down / Up&Down / Random, 1–4 octaves, rate, gate and hold (latch)
• 🌀 Master effects — modulated chorus (rate + depth) and feedback delay (time + feedback)
• 🎹 8-voice polyphony × 4 multitimbral channels with oldest-note voice stealing
• 🎛️ Glide/portamento (off / always / legato) + white & pink noise
• 🎼 37 factory presets — from sub basses to screaming leads, many ported from classic Minimoog patch charts (Parliament, ELP, Wakeman, Taurus…)
• 🎨 Minimoog-inspired GUI — custom rotary knobs, VU meter, virtual keyboard (mouse + QWERTY)
• 🎹 MIDI input with a full CC map (graceful fallback with no device)

🏗️ Architecture

┌──────────────────────────────────────────────────────────────┐
│  crate: voog  (binary)                                         │
│                                                                │
│   egui GUI  ──params/notes──►  lock-free queue  ──►  audio     │
│   (main thread)                (crossbeam)          callback   │
│        ▲                                            (cpal RT)   │
│        └──────────── VU / voices ◄─── atomics ─────────┘       │
│                                                                │
│   midir  ──MIDI events──►  same lock-free queue                │
└──────────────────────────────────────────────────────────────┘
                     │ depends on
                     ▼
┌──────────────────────────────────────────────────────────────┐
│  crate: voog-dsp  (library — no I/O, 100% unit-tested)         │
│   oscillator · moog filter · adsr · lfo · noise · glide        │
│   voice · allocator · channel · synth · presets · params       │
└──────────────────────────────────────────────────────────────┘

The real-time contract: the audio callback never allocates and never locks. The GUI and MIDI threads push events onto a lock-free ring; the callback drains them, renders one block, and publishes meters via atomics. That single discipline is what killed the dropouts.

🚀 Build & run

Tip

Run the native build for the real experience. The audio thread is allocation- and lock-free, so it's rock-solid — no clicks, no dropouts. The in-browser WASM demo is great for a quick try, but browsers schedule audio on the main thread (no cross-origin isolation on GitHub Pages → no audio worklet thread), so it can crackle or add latency. Native has none of that.

Requires a stable Rust toolchain (edition 2021).

git clone https://github.com/gpasquero/rusted-moog.git
cd rusted-moog
cargo run --release

Play with your mouse on the on-screen keyboard, your computer keyboard (A W S E D F T G Y H U J K), or a MIDI controller.

🧪 Testing

The entire DSP + engine core is pure and unit-tested — no audio device required:

cargo test --workspace   # 62 tests
cargo clippy --workspace # zero warnings

🗺️ Roadmap

• Patch save/load to disk (JSON, VOOG-compatible)
• Oversampling for the filter at high resonance
• Effects: chorus / delay / drive
• Stereo spread & unison
• Web build via WASM + WebAudio — live

🙏 Credits

Ladder filter after Antti Huovilainen's model. Pink noise via Paul Kellet's approximation. Inspired by the Moog Minimoog Model D and Subsequent 37. Rebuilt in Rust with cpal, midir and egui.

📄 License

MIT © gpasquero — see LICENSE.

_{Built because software instruments should never click.}