eurorack-js

Browser-based Eurorack modular synthesizer emulator. Patch virtual modules together with cables to create sounds.

Try it live

Modules

Sources

Module	Description
CLK	Master clock with adjustable BPM
VCO	Voltage-controlled oscillator (triangle, saw, pulse)
LFO	Low frequency oscillator with multiple waveforms
NSE	White/pink noise generator
ØCHD	8x free-running triangle LFOs (based on Instruo øchd)

Modulators

Module	Description
DIV	Clock divider/multiplier (÷16 to x16)
S+H	Dual sample & hold
QUANT	Pitch quantizer with selectable scales
ARP	Arpeggiator with chord patterns
SEQ	8-step CV/gate sequencer with direction modes
EUCLID	Euclidean rhythm generator (evenly distributed triggers)
TURING	Turing Machine - random looping sequencer (based on Music Thing)
LOGIC	Boolean gate operator (AND/OR)
MULT	2-in, 6-out signal splitter
RND	Random voltage generator (stepped/smooth outputs)
ENVF	Envelope follower (audio to CV)
FUNC	Function generator - AR envelope, LFO, slew (based on Make Noise Maths/Function)
ADSR	Envelope generator
CMP2	Dual window comparator with logic (based on Joranalogue Compare 2)

Processors

Module	Description
VCF	State-variable filter (LP, BP, HP)
FOLD	Wavefolder for harmonic complexity
RING	Ring modulator (signal multiplication)
VCA	Dual voltage-controlled amplifier
MIX	4-channel mixer with level controls
DLY	Stereo delay with time, feedback, mix
VERB	Stereo reverb with size, damping, mix
CHORUS	Stereo chorus effect
PHASER	Stereo phaser effect
FLANGER	Stereo flanger effect
CRUSH	Bit crusher / sample rate reducer
PWM	Pulse width modulator with complementary outputs

Drums

Module	Description
KICK	Analog-style kick drum synthesizer
SNARE	Analog-style snare drum synthesizer
HAT	Analog-style hi-hat synthesizer

Utility

Module	Description
ATTN	Dual attenuverter with offset (scale, invert, shift CV)
SLEW	Dual slew limiter (portamento, CV smoothing)
DB	Stereo VU meter with dB readout
SCOPE	Dual-channel oscilloscope (Scope, X-Y, Tune modes)
OUT	Stereo output to speakers

Architecture

Self-contained module system where each module is a folder containing DSP + UI:

src/js/
├── index.js              # Main entry point
├── audio/
│   └── engine.js         # DSP processing loop
├── cables/
│   └── cable-manager.js  # Cable rendering & connections
├── config/
│   ├── constants.js      # System constants
│   └── factory-patches.js
├── modules/              # Module definitions
│   └── {moduleId}/
│       └── index.js      # DSP + UI
├── patches/              # Patch serialization
├── rack/                 # Rack infrastructure
│   ├── rack.js           # Orchestration
│   └── registry.js       # Module lookup
├── ui/
│   ├── renderer.js       # Module UI generation
│   └── toolkit/          # UI components
└── utils/                # Utility functions
    ├── math.js
    ├── slew.js
    └── color.js

Creating a Module

See the Module Creation Guide for detailed documentation.

Quick example:

// src/js/modules/mymodule/index.js
export default {
    id: 'mymodule',
    name: 'My Module',
    hp: 4,
    color: '#8b4513',
    category: 'utility',

    createDSP({ sampleRate = 44100, bufferSize = 512 } = {}) {
        const out = new Float32Array(bufferSize);
        return {
            params: { gain: 0.5 },
            inputs: { audio: new Float32Array(bufferSize) },
            outputs: { out },
            leds: {},
            process() {
                for (let i = 0; i < bufferSize; i++) {
                    out[i] = this.inputs.audio[i] * this.params.gain;
                }
            }
        };
    },

    ui: {
        knobs: [{ id: 'gain', label: 'Gain', param: 'gain', min: 0, max: 1, default: 0.5 }],
        inputs: [{ id: 'audio', label: 'In', port: 'audio', type: 'audio' }],
        outputs: [{ id: 'out', label: 'Out', port: 'out', type: 'audio' }]
    }
};

Voltage Standards

• Audio: ±5V bipolar
• Gates: 0V (off) / 10V (on)
• Triggers: 5-10ms pulse at 5-10V
• Pitch CV: 1V/octave

Development

npm test         # Run tests

License

MIT