Acid Engine

A TB-303 acid synth emulation for VCV Rack 2.

Overview

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.

Installation

1. Go to the releases page.
2. Download the .vcvplugin file for your operating system. For example, AcidEngine-2.0.0-mac-arm64.vcvplugin for Apple Silicon Macs.
3. Place the downloaded .vcvplugin file into the VCV Rack plugins folder for your operating system:
   • macOS: ~/Documents/Rack2/plugins/
   • Windows: C:\Users\<Your Username>\Documents\Rack2\plugins\
   • Linux: ~/.Rack2/plugins/
4. Restart VCV Rack. Rack will automatically unzip the .vcvplugin file and delete it after installation.

Controls

Knobs

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)

Switches

Switch	Options
Waveform	Saw / Blend / Square
Mode	Baby Fish (tame) / Momma Fish (standard) / Devil Fish (extended ranges)

Inputs

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

Outputs

Output	Description
Out L / Out R	Audio output (mono, duplicated to both)

Accent Behavior

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

Mode Differences

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%

Credits

• Open303 DSP engine: Robin Schmidt (from the rosic library)
• Noise Engineering Versio Platform Port: abluenautilus
• VCV Rack Port: Vulpes79

License

MIT License