ADAT Lightpipe

showstack / protocols / adat

Also called ADAT Optical, Lightpipe, ADAT.

Eight channels of uncompressed digital audio down one plastic optical fibre, originally for a tape machine and long outliving it. Still the cheapest way to get eight channels between two boxes in a rack.

Audio transportProprietary, documentedAlesisReported

Stewarded by Alesis (originating), now a de facto standard.

Media Large, continuous, on time and in order

Continuous streams that are large enough to be sized properly, and that must arrive in order and on time.

What kills it. Anything that starves the link — usually a management transfer nobody scheduled — and jitter that outruns the receive buffer.

The four flows, and why the model is worth having →

What it carries

Sample rates: 48 kHz, 96 kHz
Audio bit depth: 24-bit
Audio channels: up to 8
Audio encoding: Linear PCM over optical

Audio: Eight channels at 48 kHz. At 96 kHz sample-multiplexing (S/MUX) pairs the channels, so the same cable carries four.

What goes wrong

The eight-channel count is at 44.1 or 48 kHz. At 88.2/96 kHz S/MUX halves it to four channels, and at 176.4/192 kHz to two. A device set to a high rate silently loses channels rather than reporting a fault.

The connector is the same TOSLINK as optical S/PDIF and carries a completely different format. They plug into each other happily.

Plastic optical fibre is short-run and bend-sensitive. Runs beyond a few metres want glass or a different transport.

Typical use

Expanding the input count of an audio interface
Linking a stagebox or preamp to a converter
Eight-channel tie-lines inside a rack

Sources

ADAT Optical Interface Specification — Alesis primary

Understand the mechanism

Show networks Numbers that stand for signals

Something wrong, or missing?

Known gaps on this entry: default_ports, first_published, implementations, spec_url. If you can source one of them, that is a ten minute pull request.

Edit this entry on GitHub — one file, editable in your browser, and your handle goes on it permanently.

Work at Alesis (originating), now a de facto standard? Confirm or correct this entry — it is free, it stays free, and nothing about it is for sale.