01.03.2006 12:00 AM
AES Digital Audio--Physical Connections
In choosing equipment with AES3 digital audio, consider your interconnection scheme. The AES standards, namely AES3 and AES3id, allow for two different types of physical connections.
AES3 employs a balanced interface with XLR-3 connectors, and 110 ohm shielded twisted pair cable. AES3id has the same data structure as AES3, but its physical connection is defined as unbalanced with BNC connectors and 75 ohm coax cable.
AES3id was developed to allow the use of video jackfields and video distribution amplifiers for distributing digital audio. So while the AES3 standard specifies a voltage level of between two and seven volts peak-to-peak, AES3id specs a more video-like voltage of one volt peak-to-peak.
Since AES3 was the original standard, there tended to be more equipment available with balanced digital audio connections. But today a variety of broadcast equipment with AES audio provides coax connections, as standard or an option, including AES routers, distribution amplifiers, A/D and D/A converters, embedders, de-embedders, and other "glue" type gear. Often both types of connectors are supplied.
For transmission type distribution and routing in a video broadcast plant, coax connections for digital audio have become very common mainly due to ease of wiring.
For digital audio control or editing rooms, it could go either way. A consideration would be what connections are used on the chosen digital audio mixer or editor and outboard gear like recorders and processors.
In can be argued that the balanced line is inherently less susceptible to noise that could cause jitter. Well-designed balanced digital audio jackfields are now readily available with easy termination systems, although rarely using the standard XLR-3 connector.