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AES3-2009; new multi-part revision published

AES3-2009 AES standard for digital audio — Digital input-output interfacing — Serial transmission format for two-channel linearly represented digital audio data has been published in a new multi-part revision at the the AES on-line store at

AES3 has been under constant review since the standard was first issued in 1985, and this multi-part edition reflects the collective experience and opinions of many users, manufacturers, and organizations familiar with equipment or systems employing AES3. Its technical content is intended to be identical to the relevant parts of the 2003 edition as amended by Amendments 5 and 6. The language has been reviewed to remove potential ambiguities -  occasionally introduced because modern technology now offers many more options that were historically available - and to improve readability.

Separating AES3 into four independently-maintainable parts in this way allows, for example, additional transmission media to be introduced in the future by revising AES3 Part 4 without affecting the other parts of AES3. Interfaces will also be able to claim compliance with AES3 Parts 1 to 3, even though they use physical and electrical techniques beyond those described in Part 4.

Part 1 Audio Content: defines the format for coding audio used for the audio content. This Part specifies the semantics of the audio data, including the "validity" flag. It also specifies the sampling frequency by reference to AES5, "AES recommended practice for professional digital audio — Preferred sampling frequencies for applications employing pulse-code modulation".

Part 2 Metadata and Subcode: specifies the format for information, metadata, or subcode transmitted with the audio data: principally the "channel status" but also User Data and the auxiliary bits. Implementors wil note that, since the "Minimum Implementation level" was retired in Amendment 6 (2008), the current implementation options ("Standard" and "Enhanced") both require that AES3 status data be implemented correctly in compliant equipment.

Part 3 Transport: defines the format for transport of an AES3 digital audio interface. 
It specifies the framing and channel coding for transmission on a unidirectional point-to-point physical link. The specified format minimizes the direct-current (DC) component on the transmission line, facilitates clock recovery from the data stream, and makes the interface insensitive to the polarity of connections.  Specific synchronization issues are covered in AES11 "AES recommended practice for digital audio engineering - Synchronization of digital audio equipment in studio operations". 

Part 4 Physical and Electrical: specifies the physical signals that convey the bit stream specified in Part 3. The transport format is intended for use with shielded twisted-pair cable of conventional design over distances of up to 100 m at frame rates of up to 50 kHz. Longer cable lengths and higher frame rates may be used, but with a rapidly increasing requirement for care in cable selection and possible receiver equalization, or the use of active repeaters. Provision is made in this standard for adapting the balanced terminals to use 75 Ohm coaxial cable, incorporating information previously published in AES-3id. Transmission by fibre-optic cable is under consideration.

Because these documents are individually maintained, they are published independently.  However, because the contents of these four documents are related, they are also available as a set. An engineering guideline document to accompany AES3, "AES-2id AES information document for digital audio engineering - Guidelines for the use of the AES3 interface", carries references to the previous edition, AES3-2003, but is in the process of amendment to refer to the new multi-part standard. Other AES documents that carry references to AES3 will also be amended where necessary.

Posted: Monday, January 18, 2010

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