A real-time audiovisual feedback instrument by Sean Stevens

Feedbax is a live visual performance tool built in Max (Cycling '74). It takes camera or video input, processes it through GPU shaders and audio-reactive feedback loops, and renders the result to a display. The core visual effect comes from a texture feedback loop — the rendered output is continuously fed back through a chain of color, rotation, and scaling transformations, creating evolving, accumulating imagery that responds to sound and gestural input.

Sean developed Feedbax over roughly 15 years (2009–2025), using it for live performances, installations, and projected visual art. This repository contains the monitor/display-focused version of the instrument, cleaned up for portability. Earlier versions of Feedbax also drove LED arrays via Open Pixel Control; those components are not included here.

Sean Stevens passed on March 9, 2026.

• Max 9 (the main patch was saved in Max 9.0.7). Download from cycling74.com. Max can open and run patches in its free mode without a license.
• A camera — any USB webcam will work. NDI network camera input is also supported.
• A microphone or audio input — Feedbax is audio-reactive. The built-in mic works, or use a line-in / audio interface.

• Mira — Cycling '74's iPad app for wireless touch control of Max patches. Feedbax uses Mira for multitouch XY control, pinch, and rotation gestures. Without Mira, you can control parameters directly in the Max patch UI.
• Ultraleap (Leap Motion) — hand tracking controller. Install the Ultraleap package from Max's Package Manager if you have the hardware. Without it, the patch falls back to iPad/UI control after a 2-second timeout.

1. Open patches/Feedbax.maxpat in Max 9.
2. The patch opens with a small preview window (320×180). To go fullscreen or change resolution, use the resolution presets in the patch (options from 1280×720 up to 7680×4320, including 3840×2160 for 4K monitors).
3. Click the toggle at the top to start the metro (frame clock). You should see the render window appear.
4. In the p picsVid subpatcher, enable a camera input (USB or NDI) or load an image/video file.
5. Adjust shader parameters via the UI controls or Mira/Ultraleap if available.
6. Audio input is live from adc~ — make sure Max's audio is turned on (Options → Audio Status) and your input device is selected.

The main shader parameters (accessible via the UI, Mira, or Leap Motion) are:

• theta — rotation angle of the feedback texture
• zoom/scale — zoom level of the feedback
• xshift / yshift — translation offset
• hue shift — rotates the color hue each feedback frame
• saturation / lightness — HSL color adjustments
• brightness / contrast — BRCOSA adjustments
• scalebright / bias — scale and bias color correction
• transparency — erase color alpha (controls how much of the previous frame persists)

The audio section (p sound2) draws waveform graphs into the GL context and generates audio-reactive "bumps" that modulate the visual parameters.

The patch is structured around a Jitter GL rendering pipeline with a texture feedback loop:

metro (configurable, default 60hz)
  │
  ├─ erase → jit.gl.render "foo"
  │
  ├─ p picsVid ─── camera/NDI/video/image input
  │                 chromakey + lumakey
  │                 → jit.gl.layer (composited into GL context)
  │
  ├─ p sound2 ──── adc~ (microphone)
  │                 → FFT analysis → jit.catch~
  │                 → jit.gl.graph (waveforms drawn into GL context)
  │                 → audio-reactive parameter modulation
  │
  ├─ p shaderfx ── receives rendered texture + control params
  │                 → td.rota.jxs (rotation / zoom / offset)
  │                 → jit.gl.pix (HSL hue shift, saturation, lightness)
  │                 → cc.scalebias.jxs (scale + bias)
  │                 → jit.gl.pix brcosa (brightness / contrast / saturation)
  │
  ├─ FEEDBACK LOOP:
  │    jit.gl.texture "fst" (full resolution, e.g. 3840×2160)
  │      ↕ switch toggles between fst/dst
  │    jit.gl.texture "dst"
  │      → p shaderfx → jit.gl.videoplane → back into GL context
  │
  └─ jit.window "foo" → display output

Control input flows through two paths that pack a 9-float vector (theta, scale, yshift, xshift, scalebright, bias, hue, NC, sat):

• p webUI — Mira iPad multitouch + on-screen controls → s shadeCtl
• p LeapGemini — Ultraleap hand tracking → s shadeCtlLeap (overrides iPad when hands are detected)

All shader files referenced (td.rota.jxs, cc.scalebias.jxs, co.chromakey.hsv.jxs, co.lumakey.jxs) are standard Max/Jitter builtins. The brcosa gen patcher and the custom HSL-shift jit.gl.pix are compiled inline in the .maxpat JSON.

patches/
  Feedbax.maxpat               ← main patch (Max 9)
  variants/
    Feedbax Ultrawide.maxpat   ← multi-monitor/ultrawide support with oversampling (Max 8)
assets/
  NormalFullAlpha1080p1.png    ← full-frame opaque alpha mask (loaded on startup)
  circleGradiant1080p6.png     ← circular gradient alpha mask (vignette effect)
input/
  transparent-background/      ← put your sticker/overlay images here (organized in subdirectories as you like)
output/                        ← screenshots save here
docs/
  *.png                        ← screenshots of each subpatcher for reference
version.txt                    ← current version identifier

The Ultrawide variant adds multi-monitor resolution presets (e.g. 6400×1800 for dual ultrawides), oversampling controls, and dual-screen screenshot capture. It was saved in Max 8.6.x but should open in Max 9.

Sticker images: Place your transparent-background images (PNGs with alpha channels) in input/transparent-background/. You can organize them in subdirectories — the patch scans recursively. On load, the patch automatically resolves its own location and finds the input/ directory relative to the project root.

Alpha masks: The main patch expects the alpha mask images in assets/ to be findable by Max's search path. The simplest approach: in Max, go to Options → File Preferences and add the assets/ folder to the search path. Alternatively, copy the two PNG files into the same directory as the patch.

Screenshots: Captured screenshots save to the output/ directory in the project root.

Feedbax evolved through several generations:

• 2009–2013 — early versions driving LED arrays via Processing and Color Kinetics hardware
• 2010–2016 — "Feedbax LED" series (v3.86 through v4.4b15), using Jitter matrix processing for LED output via Open Pixel Control and DMX/ArtNet
• 2013–2019 — "Synesthesia Analog Analog" — a related instrument focused on audio-to-visual synthesis
• 2019–2024 — "Feedbax gl + image" series, rebuilt around Jitter's GPU/OpenGL pipeline (jit.gl.pix, jit.gl.slab, jit.gl.render) for high-resolution monitor output
• 2024–2025 — "DeployabilityCleanup" builds (v121–v123), streamlining the patch for portability and ease of use

MIT

Created by Sean Stevens.

Open-sourced posthumously by Ethan Fremen.