SC-02-02 meeting, Barcelona, 2005-05

Report of the SC-02-02 Working Group on digital input/output interfacing of the SC-02 Subcommittee on Digital Audio held in Barcelona, Spain on 2005-05-26.

The meeting was convened by chair, J. Grant.

The Agenda and the report of the previous meeting, held in San Francisco 2004-10-26 were approved. R Caine remarked that, while it correctly reported the discussion of an annex to AES11 describing the synchronisation of multiple sampling frequencies from a single sinusoidal tone, and had referred to it as annex B, the annex in question is actually annex D.

Note: projects appear in this report in the order in which they were discussed; this was different from the order in which they appear on the agenda so as to (a) accommodate some members who could not be present for the whole meeting and (b) take related projects together.

AES-X119: Standard, Connector for AES3 interfaces
J. Brown presented a graph showing that the frequency response of some cables currently used for AES3 is very similar to that of Cat5 cables and of similar branded cables such as MediaTwist. Other AES3 cables have a poorer high frequency response, though still better than Cat3 cables.

The replies to the questionnaire showed that there is a case for including the XLD in AES3, though Caine pointed out that we cannot at this stage change AES3 to require its use, only to recommend it or to present it as an alternative with no preference indicated. Specification of the connector itself, and of cables to be used with it, is a specialist task that should be handled by SC-05-02.

The meeting proposed to request SC-05-02 to develop a specification for the XLC and XLD to which AES3 can make reference.

[NOTE: A writing group consisting of Caine, Brown, and Grant produced an initial draft for the amendment to AES3 after the meeting.]

New goal: draft amendment; date: 2005-06.

AES3-R: Revision of AES3-1992 (r1997): AES Recommended practice for digital audio engineering -- Serial transmission format for two channel linearly represented digital audio data
Caine presented a proposed new structure for AES3, which could be in either two or four parts, rather than the three parts originally envisaged. The meeting preferred four parts. The next step will be to cut and paste the existing text into the new structure, also including some text from AES-2id and AES-3id. The description of channel status needs revision, and a profile in which transformers are mandatory was recommended.

Task Group SC-02-02-C would be the appropriate forum for the writing group;

New goal: initial draft of PTD, date 2005-10.

AES-2id-R: Review of AES-2id-1996: AES information document for digital audio engineering -- Guidelines for the use of the AES3 interface
Caine reported that input is needed for clauses 4 and 5.

New goal date 2005-10.

AES-3id-R: Review of AES-3id-2001: AES information document for digital audio engineering -- Transmission of AES3 formatted data by unbalanced coaxial cable
No action required or proposed.

AES5-R: Review of AES5 2003: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
No action required or proposed.

AES10-R: Review of AES10-1991 (r1997): AES Recommended Practice for Digital Audio Engineering -- Serial Multi-channel Audio Digital Interface (MADI)
No action required or proposed.

AES-10id-R: Review of AES-10id-2005: AES information document for digital audio engineering -- Engineering guidelines for the multi-channel audio digital interface (MADI) AES10
No action required or proposed.

AES18-R: Review of AES18-1996 (r2002): AES recommended practice for digital audio engineering -- Format for the user data channel of the AES digital audio interface
R Caine will ask IABM whether any of their members are using AES18.

AES41-R: Review of AES41-2000: AES standard for digital audio -- Recoding data set for audio bit-rate reduction
No information had been forthcoming in response to enquiries whether this standard is used. No revision is required but reaffirmation leaves open the possibility of revision in the future. The meeting recommended to reaffirm.

AES47-R: Review of AES47-2002: Digital Audio in asynchronous transfer mode (ATM)
An amendment is required to (1) insert the AES OUI value (to align the text with IEC 62365), and (2) revise 4.3.2 and Table 2 to relax the requirements for conformance. No amendment for DSD (see X144 below). Grant to produce text.

AES-R4-R: Review of AES-R4 2002: Guidelines for AES standard for digital audio - Digital input-output interfacing - Transmission of digital audio over asynchronous transfer mode (ATM) networks, AES47
No action required or proposed.

AES-X111: Transmission of the unique material identifier (UMID) on AES3
The meeting recommends the current draft proceed to PCFC.

AES-X121: Synchronisation of digital audio over wide areas
Grant reported that no contributions to this document had been forthcoming, but the document could be revisited later to consider the effect of evolution of practices in the field.

New goal date 2006-01.

AES-X140: High Resolution Multichannel Audio Interconnection
AES-R6 has been published. AES50-xxxx is currently out for public comment and therefore could not be discussed.

AES-X139: Liaison with EBU P/AGA
R Chalmers reported that P-AGA met at BBC Kingswood Warren on 16-17 December 2004, but very little of the discussion concerned items of interest to SC-02-02. The publication of IEC 62365 was reported to them.

AES-X143: Transmission of asynchronous transfer mode (ATM) over an Ethernet physical layer
Grant to produce a revised PTD incorporating the changes in the e-mail to the TG of 2005-02-23, and adding an extension mechanism which will allow the issues raised in the e-mail of 2005-05-13 to be addressed later.

New goal dates: PTD 2005-06; PWD 2005-07.

AES-X144: Carriage of DSD audio data in AES47
As there is still no draft, the group recommended that this project should be retired forthwith.

AES11-R: Review of AES11-1997: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations
Annex B: D. Josephson, D. Hill, and Caine to redraft this annex. A new standard should be produced to specify "word clock" and AES11 amended to refer to that, in the same way that a DARS is currently specified by reference to AES3.

Annex D: The draft recently circulated should be incorporated in a new printing of AES11; no CFC is required because this annex is not normative.

AES-X148: Sample-accurate timing in AES47
The problem with the current draft is that in some applications timing may be realigned periodically, for instance at midnight. Grant to redraft so that it does not specify the origin of the timing but recommends the epoch specified in SMPTE 404. New goal date 2005-06.


SC-05-02 is formally requested to specify the XLC and XLD connectors outlined in the AES-X119 report.

Grant reported that IEC PT62379 would meet on the Friday to further progress the Common Control Interface draft.

J. Yoshio reported that IEC MT60958 would meet on the Saturday. They are proposing use of the U-channel to convey timing information which would allow lip sync to be maintained when there are significant delays in the video path, for instance for display devices to process the video to enhance video quality. There is a potential conflict between this use of the U-bit and the use specified in AES-X111.

SMPTE should also be made aware of AES-X111.

New Projects

No new projects were proposed

New Business

No new business was proposed

The next meeting is scheduled to be held in conjunction with the 119th AES Convention, New York, NY., US., 2005-10.

AES - Audio Engineering Society