SC-02-02 meeting, Rome, 2013-05

Report of the meeting of the SC-02-02 working group on digital audio interfaces, of the subcommittee on digital audio, held in Rome on 2013-05-04

The meeting was convenened by chair J. Grant.

The agenda, and the report of the previous meeting held in San Francisco on 2012-10-26 were approved as written.

Projects assigned to this group but not mentioned here had no action requested or required - see for details.

Open Projects

AES5-R Review of AES5-2008: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
The meeting recommended that AES5-2008 be reaffirmed.

AES10-R Review of AES10-2008: AES Recommended Practice for Digital Audio Engineering - Serial Multichannel Audio Digital Interface (MADI)
It was felt that this standard should be reaffirmed (subject to editorial corrections for fibre diameter in 7.2.1 and mismatch between the Abstract and clause 5 re number of channels), although action was postponed until the New York meeting in case any revisions are required to accommodate AES-X213.

AES11-R Review of AES11-2009: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations
Secretariat to make changes and circulate to the working group for comment.

AES41-R: Review of AES41-2009: AES standard for digital audio - Recoding data set for audio bit-rate reduction
The 2012 version has now been published, in 5 separate parts.

AES55-R: Review of AES55-2007: AES standard for digital audio engineering - Carriage of MPEG Surround in an AES3 bitstream
The 2012 revision has now been published.

AES-2id-R: Review of AES-2id-2006: AES information document for digital audio engineering - Guidelines for the use of the AES3 interface
The 2012 revision has now been published.

AES-R8: AES standards project report - Synchronisation of digital audio over wide areas
An e-mail from M. Law has now been circulated to the WG reflector, proposing a revision to the last paragraph of the draft regarding quality of the timing reference. This would also imply a change in the meaning of byte 4 bits 0 and 1 in AES3 channel status to signal the accuracy of the sampling frequency even when the signal is not a DARS.

This provoked a wider discussion on whether a more comprehensive revision of AES3 channel status would be appropriate. This has evolved considerably in the 3 decades since it was first specified. Alternatively, the information that channel status does not currently support might be better carried as out-of-band metadata.

M. Yonge suggested that bytes 6 to 22 are no longer used, and might be used for a "version 2" channel status, leaving the specification of the existing channel status bits unaffected.

S. Heinzmann suggested that, rather than redefining channel status, it would be useful to clarify which channel status bits apply to the audio content and which to the data transport. This would in turn clarify which bits should be updated when a signal is passed through a router, or tunnelled through other transport formats such as IEC 61883-6 or MADI. This could be added as a annex to Part 2 of AES3.

AES-X182: AES/Ethernet Simple Open Protocol
A new draft, which is expected to be the final task-group draft, was uploaded to the SC-02-02-J document area on 2013-05-02, and is awaiting task-group approval.

AES-X196: Use of AES3 with high sampling rates to carry multi-channel audio
There has been no further progress on deciding between the two proposed options for identifying the channels (A: use Y preamble for all channels except the first, or B: set the C bit in the second subframe of a frame to 1 for the last channel). It is very possible that each of them will work with some applications but not others, and in many cases it will be easy to design equipment so that it supports both. Secretariat to draft a standard specifying both formats from the document previously provided by the BBC.

AES-X213: MADI over twisted-pair cabling
M. Brunke reviewed the areas in which the proposal, using a balanced signal, differs from using the same format on co-axial cable. It supports 100 m cable lengths, with better EMC performance. When there are 32 channels, synchronisation symbols need to be bunched together to achieve the necessary inter-packet gap; this does not meet 4.3.2 of AES10 (requirement for at least one synchronisation symbol per frame period) but does allow 6.3 (phase relationship to master clock) to be met. A new draft, which should to be the final TG draft, is expected soon.


J. Yoshio reported that IEC TC100 TA4 is revising Parts 1 and 3 of IEC 60958. Part 1 revision includes updating references to SMPTE documents, especially those specifying codes to identify compressed audio formats. Part 3 revision includes reference to new channel assignments in IEC 62574, including for 22.2, and loudness metadata. PT60958 is meeting in Rome on 6th May, after which both Parts will go for CDV ballot.

P. Treleaven reported that SMPTE will be implementing the same extensions to the compressed audio formats code space, and have included provision for avoiding code points that cold be mistaken for synchronisation codes.

New projects:

No new projects were proposed.

New business:

There was no new business

The next meeting will be held in conjunction with the 135th Convention in New York, 17 to 20 October 2013.

AES - Audio Engineering Society