Dolby Laboratories UEX/650 Installation Instructions Manual - Page 12

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Digital Audio Inputs

There are two professional interface formats used for digital audio: AES/EBU (also

known as AES3) and AES-3id. These stream the same digital data and professional

audio header information over copper conductor links, but use different types of

conductors and connectors.

AES/EBU uses a balanced connection (two conductors plus shield) with a

characteristic input impedance of 110Ω, nominal peak-to-peak signal level of 5 V,

and, most commonly, XLR connectors. The typical maximum transmission distance

is 100 meters (328 feet). AES-3id uses an unbalanced connection (one signal

conductor plus shield) with a characteristic input impedance of 75Ω, peak-to-peak

signal level of 1V, and BNC ("push and twist") connectors. The typical maximum

transmission distance is 1,000 meters (3,280 feet).

Professional digital audio equipment usually uses the AES/EBU format because

balanced operation yields superior noise immunity, as it does with analog audio

signals, and because XLR connectors have been standard on analog professional

audio equipment.

Professional video equipment usually uses the AES-3id variation of this interface,

with BNC connectors. As with the use of XLR connectors on pro audio equipment,

the adoption of BNC connectors for the audio on professional video equipment stems

from their existing use for the video signal. Also, the unbalanced AES-3id signal can

connect to more than one piece of equipment by using the loop-through connectors

available on some devices, and is robust for long cable runs.

8.1

Consumer Interface Standards for Digital Audio

The consumer interface standard for digital audio is S/PDIF (IEC61937). S/PDIF is

found using either coaxial unbalanced connections (one signal conductor plus shield)

with a characteristic input impedance of 75Ω with RCA (phono) connectors, or a

fiber-optic cable with Toslink

peak-to-peak signal level of 0.5 V. The typical maximum transmission distance is

10 meters (33 feet). Although S/PDIF-specific cables with suitable connectors can be

purchased, you can also get good results using high-quality 75Ω video cable with the

appropriate connectors and/or adapters.

8.2

Cable Issues

Even in digital audio, noise-free signals are still very important. The cable used for

digital signals is specifically designed for digital audio use even though it appears to

be the same as that used for analog audio or video signals. Any professional audio

equipment or broadcast supply company can provide 110Ω cable with connectors (or

without, if you wish to terminate them yourself) for AES/EBU connections, and high-

quality 75Ω video cables with BNC connectors for AES-3id connections. Use of

cables or connectors not designed for digital transmission or with incorrect

Dolby

UEX/650 Upgrade Kit Installation Instructions

connectors. The unbalanced coaxial connection has a