Report of the meeting of the SC-02-02 working group on digital audio interfaces, of the subcommittee on digital audio, held in Warsaw, Poland, 2015-05-07
The meeting was convened by chair J. Grant.
The agenda, and the report of the previous meeting, held in Los Angeles, 2014-10-09, were approved as written.
Projects assigned to this group but not mentioned here had no action requested or required - see www.aes.org/standards/meetings/project-status.cfm for details.
Open Projects
AES3-x-R: (x = 1 to 3) Review of AES3-x-2009, AES standard for digital audio - Digital input-output interfacing - Serial transmission format for two-channel linearly represented digital audio data (first three of four parts)
These documents have now been reaffirmed. No issues were raised at the meeting.
AES3-4-R: Review of AES3-4-2009, AES standard for digital audio - Digital input-output interfacing - Serial transmission format for two-channel linearly represented digital audio data - Part 4: Physical and electrical
J Paul presented a summary of the issues raised in Task Group SC-02-02-N, and there was a long discussion of them. A new draft of both documents is expected by mid-September. The new draft will need to be checked for compatibility with AES42, particularly as regards phantom power, which might saturate any normal mode (differential mode) EMI chokes. Also, AES42 may need to be revised to refer to the updated AES3-4 and AES-2id.
Liaison is also needed with SC-05-05 regarding EMC, though it was noted that several of the TG members are also participating in SC-05-05.
S. Heinzmann pointed out that, in the currently-published version, rise and fall times are specified as percentages of a Unit Interval (UI), which makes it difficult to design equipment to meet both the minimum rise time at low sampling frequencies and the maximum at high frequencies. The meeting felt that a minimum rise time should not be specified; a designer might choose to use a slower rise time to (for example) reduce electromagnetic emissions or ringing but that can also be achieved by other means, and should be specified by more appropriate figures such as return loss.
The new draft will recommend that cables should be specified for frequencies of 640 Fs, because cables that roll off above 128 Fs are currently often used and give a very poor eye pattern.
The use of transformers will not be required by the standard, as it was felt that implementers should be able to choose what components they use to meet the requirements. However, the Information Document will give advice on best practice in cases where they are used.
AES-2id-R: Review of AES-2id-2006 (r2012): AES information document for digital audio engineering - Guidelines for the use of the AES3 interface
The intention is to revise AES-2id at the same time as AES3-4; it would not otherwise need to be reaffirmed until 2017.
AES5-R Review of AES5-2008: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
No issues were raised at the meeting.
AES10-R: Review of AES10-2008: AES Recommended Practice for Digital Audio Engineering - Serial Multichannel Audio Digital Interface (MADI)
Task group SC-02-02-M has been formed to handle revision of AES10 and AES-10id; SC-02-02-L's scope is now restricted to AES-X213. There has been no activity in SC-02-02-M since mid-January.
AES11-R Review of AES11-2009: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations
This document has now been reaffirmed. No issues were raised at the meeting.
AES-R8: AES standards project report - Synchronisation of digital audio over wide areas
Further revision to the text is required following discussion on the reflector earlier this year.
Development Projects:
AES-X182: AES/Ethernet Simple Open Protocol
Secretariat formatting is still awaited; secretariat to check with TG chair whether there are any changes to the proposed specification.
AES-X196: Use of AES3 with high sampling rates to carry multi-channel audio
There has still been no input from the organisation that originally requested this project.
AES-X213: MADI over twisted-pair cabling
A final TG draft is still awaited. Secretariat received some documents shortly before the meeting, which will be uploaded to the TG document area.
Liaisons:
J Yoshio reported that at its April 2015 meeting in Milan, TC100 approved a project for enhancement of IEC 60958 to support more than 24 bits per sample and more than 2 audio channels. Previously it had been proposed that HDMI should be used for these use cases, but now the view is that HDMI is overly-complex to be used for audio-only applications, which might also be affected by revisions made for the purpose of supporting new video formats.
The new project will revise 60958-1, 60958-3, and 61937-1, and possibly also write a new Part, 60958-5 Enhanced Consumer Applications. In the current proposal for the new format there is a "multi-frame" for each sample, consisting of a number of frames, and a new preamble which is used to mark the first frame of a multi-frame. This is more similar to MADI (where the "subframe 0" flag would correspond to the new preamble) than to the proposals consdered in AES-X196. A pair of subframes can be aggregated to give 48 audio bits to support formats needing more than 24 bits, including floating-point formats.
P Treleaven reported that SMPTE will be updating their standards to match the additions to 61937.
New projects
No new projects were proposed.
New business
There was no new business.
The next meeting will be scheduled in conjunction with the AES 139th Convention in New York, NY., US., 29 October to 1 November, 2015.
