AES3

showstack / protocols / aes3

Also called AES/EBU, AES-3, IEC 60958 Type I.

Two channels of uncompressed digital audio down one balanced pair, self-clocking, on the XLR connector everything else on the stage already uses. It is the reason a digital feed can travel a mic line, and the reason people plug digital into analogue inputs by mistake.

Audio transportPaid specAESReported

Stewarded by AES (Audio Engineering Society), with the EBU.

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: 32 kHz, 44.1 kHz, 48 kHz
Audio bit depth: 24-bit
Audio channels: up to 2
Audio encoding: Linear PCM, biphase mark coded

Audio: Two channels in one subframe pair. Later revisions add higher rates, and the consumer variant of the same electrical idea is S/PDIF.

What goes wrong

The cable is 110 Ω, not the 45–75 Ω of a normal mic line. A standard XLR cable often works over a short run and then fails as the run gets longer, which makes it one of the more misleading intermittent faults on a stage.

It is self-clocking, so the receiver locks to the sender. Two devices that are both trying to be clock master produce dropouts rather than an error.

S/PDIF carries the same data format on 75 Ω coax at a much lower voltage. They interconvert, but not by rewiring a connector.

Plugging AES3 into an analogue input sends a wideband square wave into a preamp. It is loud, it is unpleasant, and on some systems it is expensive.

Typical use

Two-channel digital feeds between consoles, processors and amplifiers
Digital output from playback machines and broadcast equipment
The transport under many older matrix and distribution systems

Sources

AES3 — Serial transmission format for two-channel linearly represented digital audio data — Audio Engineering Society primary
Interfacing AES3 and S/PDIF (RaneNote 149) — Rane Corporation
IEC 60958 — Digital audio interface — International Electrotechnical Commission primary

Understand the mechanism

Show networks Numbers that stand for signals

Something wrong, or missing?

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

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Work at AES (Audio Engineering Society), with the EBU? Confirm or correct this entry — it is free, it stays free, and nothing about it is for sale.