Sleepy Circuits Hypno
A semi-modular video synthesizer that transforms your Eurorack system into an audio-visual playground
What is Hypno?
A Raspberry Pi-powered video synthesizer inspired by analog video systems, condensed into a compact, CV-controllable device
Digital Analog Dreams
The Hypno digitally emulates and extends common analog video workflows that previously required entire systems to achieve. It combines shape generation, colorization, and feedback into a simple, compact interface that integrates seamlessly with modular synthesizers.
At its core, Hypno runs GLSL shaders on a Raspberry Pi, translating knob movements and CV signals into mesmerising visual patterns. The device accepts standard Eurorack voltage ranges (−5V to +5V), making it immediately compatible with your existing modular setup.
- Two oscillators with selectable shapes, frequency, rotation, and polarisation
- Four feedback modes with positive and negative gain
- OKLab colorizer for perceptually uniform colour transitions
- Internal patching matrix for complex modulation routing
- Video input via USB webcams or capture cards
Hypno Version 1 — Now Discontinued
The original Hypno (Version 1) has been discontinued and replaced by Hypno 2. However, Version 1 remains a powerful and capable device with ongoing firmware support. This page documents its use with Eurorack modular systems.
How Hypno Works
Understanding the video synthesis engine
Oscillators
Two independent oscillators generate shapes that can be bars, circles, rings, or complex patterns. Each has controls for frequency, rotation, and polarisation (switching between cartesian and polar coordinates).
Fractals
Each oscillator can be fractalized, creating intricate repeating patterns. The fractal amount and angle can be adjusted to produce everything from subtle texture to kaleidoscopic complexity.
Feedback
The central gain control determines overall amplitude. Past the midpoint, the frame begins to feedback on itself. Four feedback modes create different visual characteristics from smooth trails to harsh distortion.
Colorizer
The OKLab colorizer maps luminance values to a colour palette with perceptually uniform transitions. This ensures smooth, pleasing colour changes as parameters are modulated.
CV Control from Your Modular
Connect your Eurorack system to create synchronised audio-visual performances
Voltage Control
Hypno accepts standard Eurorack CV signals in the −5V to +5V range — different from LZX video synthesizers which use −1V to +1V. This wider range makes Hypno immediately compatible with audio-rate Eurorack modules.
Seven CV inputs and two trigger inputs allow comprehensive control over the visual parameters. Use LFOs for slow, evolving changes, envelopes for reactive animations, or audio-rate signals for glitchy, textural effects.
| Input | Controls |
|---|---|
| CV 1–2 | Oscillator 1 & 2 Shape/Frequency |
| CV 3–4 | Rotation & Polarisation |
| CV 5–6 | Feedback Amount & Mode |
| CV 7 | Colorizer Position |
| Trig 1–2 | Preset Recall / Random |
MIDI Control
In addition to CV, Hypno acts as a USB-MIDI host. Connect MIDI controllers, keyboards, or sequencers directly to control parameters. All knobs are mapped to MIDI CC on channel 16. Use the CME WIDI Bud Pro for wireless MIDI from your computer or other devices.
Eurorack + Hypno Combinations
Creative ways to synchronise your audio and visuals
Envelope Follower Visuals
Use an envelope follower on your audio output to extract amplitude. Route this CV to Hypno's feedback amount for visuals that pulse with your music.
Clock-Synced Colour Changes
Divide your master clock and use the divided triggers to step through Hypno's presets, creating colour palette changes on the beat.
LFO-Driven Rotation
Patch slow LFOs to oscillator rotation inputs. Use different rates and shapes for each oscillator to create complex, evolving kaleidoscopic patterns.
Random Voltage Textures
Sample and hold or noise sources create unpredictable, glitchy visual textures. Great for harsh noise or experimental performances.
Sequenced Feedback
Use a step sequencer to automate feedback mode and amount changes. Sync to your musical sequence for visuals that follow your composition.
Audio-Rate Modulation
Patch oscillator outputs directly into Hypno's CV inputs for extreme, glitchy textures. Attenuate heavily for usable results.
External Video Sources
Process live video or loop MP4 files through Hypno's shader engine
USB Webcam Input
Connect a UVC-compliant USB webcam (USB 2.0, MJPEG) to process live video through Hypno’s oscillators and feedback engine. Great for processing your own face or environment.
Capture Card Input
Use a USB capture card to bring in external video sources — game consoles, other video synths, or camera feeds. Hypno replaces one oscillator with the video input.
USB Video Looping
Load MP4 videos (720×480, 30fps) from a USB drive. Navigate folders with the built-in UI and use your videos as oscillator sources for processing.
Video Packs
Sleepy Circuits offers numerous video packs designed specifically for Hypno — abstract patterns, textures, and loops optimised for processing and feedback.
Specifications
| Video Output | HDMI (720×480 SD), Composite via 3.5mm (PAL/NTSC) |
| Video Input | UVC webcams, USB capture cards, MP4 from USB drive |
| CV Inputs | 7× CV (−5V to +5V), 2× Trigger (rising edge) |
| MIDI | USB Host (Channel 16) |
| Processor | Raspberry Pi 3B+ or Pi 4 (4-core) |
| Power | USB-C, 5V 3A recommended |
| Connectivity | WiFi, Bluetooth, Ethernet (model dependent) |
| Streaming | NDI output via USB for OBS/Resolume integration |
| Presets | 3 onboard, unlimited via USB/MIDI |