A TB-303 acid synth emulation for VCV Rack 2.
Acid Engine brings the iconic sound of the Roland TB-303 to VCV Rack, featuring authentic filter squelch, accent behavior, and slide. The module offers three operational modes ranging from tame to wild.
Pre-built .vcvplugin files for all supported platforms are available on the releases page.
| Platform | Architecture | File |
|---|---|---|
| macOS (Apple Silicon) | arm64 | AcidEngine-<version>-mac-arm64.vcvplugin |
| macOS (Intel) | x86_64 | AcidEngine-<version>-mac-x64.vcvplugin |
| Windows | x86_64 | AcidEngine-<version>-win-x64.vcvplugin |
| Linux | x86_64 | AcidEngine-<version>-lin-x64.vcvplugin |
Method A — Rack menu (recommended)
In VCV Rack, choose Library → Install Plugin from File… and pick the downloaded .vcvplugin file. Restart Rack when prompted.
Method B — Drop into the plugins folder manually
Place the .vcvplugin file in the plugins folder for your platform/architecture:
| Platform | Folder |
|---|---|
| macOS (Apple Silicon) | ~/Library/Application Support/Rack2/plugins-mac-arm64/ |
| macOS (Intel) | ~/Library/Application Support/Rack2/plugins-mac-x64/ |
| Windows (x64) | %LOCALAPPDATA%\Rack2\plugins-win-x64\ |
| Linux (x64) | ~/.local/share/Rack2/plugins-lin-x64/ |
Restart VCV Rack. Rack unzips the .vcvplugin automatically on first launch.
Requires the VCV Rack SDK. Set RACK_DIR to point at your SDK and run:
make dist -jThe packaged plugin is written to dist/AcidEngine-<version>-<platform>.vcvplugin.
To cross-compile for Intel macOS from an Apple Silicon host:
CROSS_COMPILE=x86_64-apple-darwin make dist -jEvery push runs .github/workflows/build.yml, which builds .vcvplugin artifacts for mac-arm64, mac-x64, win-x64, and lin-x64. Pushing a v* tag attaches all four artifacts to a GitHub Release automatically.
| Knob | Description |
|---|---|
| Tuning | Master tuning offset (+/- 12 semitones) |
| Cutoff | Filter cutoff frequency |
| Resonance | Filter resonance amount |
| Decay | Filter envelope decay time |
| EnvMod | Filter envelope modulation depth |
| Slide | Portamento/glide time between notes |
| Accent | Intensity of accent effect (squelch + volume boost) |
| Switch | Options |
|---|---|
| Waveform | Saw / Blend / Square |
| Mode | Baby Fish (tame) / Momma Fish (standard) / Devil Fish (extended ranges) |
| Input | Description |
|---|---|
| V/Oct | Pitch CV (1V/octave) |
| Trig | Gate/trigger input |
| Accent | Gate input (>2.5V triggers accent on that note) |
| Cutoff CV | Filter cutoff modulation |
| Res CV | Resonance modulation |
| Decay CV | Decay time modulation |
| Slide CV | Slide amount modulation |
| EnvMod CV | Envelope mod depth modulation |
| Output | Description |
|---|---|
| Out L / Out R | Audio output (mono, duplicated to both) |
The accent works like a real 303:
- Accent knob controls the intensity (how much squelch and volume boost)
- Accent CV acts as a gate - send >2.5V to accent that note
- Accented notes get: faster filter envelope (5x shorter decay), extra cutoff modulation, and amplitude boost
| Parameter | Baby Fish | Momma Fish | Devil Fish |
|---|---|---|---|
| Cutoff | 200-2000 Hz | 100-4000 Hz | 20-8000 Hz |
| Resonance | 0-50% | 0-80% | 0-100% |
| Decay | 200-1000 ms | 200-2000 ms | 30-3000 ms |
| EnvMod | 0-50% | 0-80% | 0-100% |
| Accent | 0-25% | 0-50% | 0-100% |
- Open303 DSP engine: Robin Schmidt (from the
rosiclibrary) - Noise Engineering Versio Platform Port: abluenautilus
- VCV Rack Port: Vulpes79
MIT License