Compander
AI-assisted project. This codebase was created with Claude
(Anthropic), directed and reviewed by a human author. The signal model is
verified numerically by an offline harness that drives the real plugin class:
it checks the compander's round trip against its own algebra, checks the
parallel envelope detector against a strictly serial implementation of the same
law, and proves the effect acts along the scan and not across it (see
Status). The FFGL build has been loaded into Resolume Arena 7.27.1, put on a
layer and run on real footage, with its controls, groups and factory presets read back
out of the running host. No audio spectrum has ever reached it, though: the
audio-reactive controls are wired up and Resolume recognises them, but they've never been
driven. The OpenFX build has only ever been exercised by a test probe, and has never been
opened in Resolve. Check it in your own rig before you trust it in a show.
An analogue radio mic's companding circuit, with your footage pushed through it
instead of a microphone signal, as an FFGL plugin for Resolume
Arena and Avenue, and the same thing again as an OpenFX plugin for Resolve, Nuke,
Natron and Vegas.
The project page has the downloads, the user guide and the video.
A wireless link can't carry the dynamic range of what's sent down it. So the
transmitter squashes it (pre-emphasis to lift the quiet top end above the noise,
then a compressor that halves the signal's excursion in dB) and the receiver
does the exact opposite, expanding it back out and de-emphasising. In between
sits a link with a noise floor, a ceiling, and no opinion about either.
in → EMPHASIS → COMPRESS → [ link: level, ceiling, noise ] → EXPAND → DE-EMPHASIS → out
Get every stage right and almost nothing happens: a working radio mic sounds
like a cable. Everything this plugin is for comes from the two ends disagreeing.
Video: What it does, in 50 seconds
Browser demo: compander-demo.stoatworks-labs.com, the plugin's own shaders in WebGL2, no install. It's a demo, not the plugin; see below.
Rendered by the plugin's own offline harness in a headless GL context rather than captured from Resolume. Actual frames through the shipped shaders, on a synthetic scene built to make companding measurable: a flat band, hard vertical edges, two one-pixel combs at ninety degrees to each other, and a ramp.
Download
v0.1.4 — prebuilt for macOS, Windows and Linux. Pick your platform:
All builds, checksums and release notes: github.com/stoatworks-labs/compander/releases.
macOS builds are signed and notarised and open normally. The Windows builds are unsigned, so SmartScreen warns once.
What it does
- Compress and Expand are set independently, so you can run half the
chain. Compress with nothing expanding and the picture goes flat and bright,
shadows lifted off the floor, edges screaming. Expand with nothing compressed
and it goes contrasty and dead, blacks crushed, fine detail sucked out of
anything dim.
- Emphasis is the pre-emphasis network, in dB of lift on the detail band.
- Tilt is the mismatch between the two emphasis networks: matched in the
middle, no de-emphasis at all at the top, de-emphasised twice at the bottom.
- Link Level, Noise and Headroom are the link itself. Drop the level
and the signal sits closer to a noise floor that hasn't moved, so the expander
restores the picture and the hiss by different amounts and the shadows breathe.
- Time Constant is the one that makes this a video effect rather than an
audio compressor pointed at a picture. See below.
- Sidechain can hand the compressor a real audio envelope instead of the
picture's own. A compander is a circuit whose gain is driven by an audio
envelope, so this is the circuit being fed the kind of signal it was built for,
with the picture standing in for the carrier.
The time constant is a distance
A signal on a wire has one axis, time. When that signal is a picture, time is the
scan. So a compander's attack and release convert, exactly, into a distance
along the line:
This is the beginning of the README. Read the rest at the original. Read the full README ↗
