Report of the meeting of the SC-02-02 working group on digital audio interfaces, of the subcommittee on digital audio, held in New York, NY, USA, 2017-10-19.
The meeting was convened at 14:05 by chair J. Grant, participating remotely from the UK.
The agenda, and the report of the previous meeting, held in Berlin, Germany, 2017-05-20, 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:
AES3-4-R: Review of AES3-4-2009 (r2014), 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
and AES-2id-R: Review of AES-2id-2006 (r2012): AES information document for digital audio engineering - Guidelines for the use of the AES3 interface
J Paul and R Cabot started the discussion with the required bandwidth (number of Manchester code nulls) to give best recovery of data, between the theoretical X1 (FS x 128) as in the existing AES 3-4, and the observed X5 (FS X 640) proposed.
R Cabot said the experiment by J Paul, used long cables to filter the transmitted AES signal, with phase and other distortions. This led to discussion of cables for AES/EBU and AES 2id. J Paul mentioned that the number of nulls experiment to determine required bandwidth should be repeated with passive filters rather than cables.
R Cabot discussed the use of pre-emphasis. Details of receivers and transmitters such as RS-422 and RS-485 were also discussed.
There is a trade-off between cable characteristics and measures such as pre-emphasis in the interfaces, and other issues raised in J Paul's SMPTE 2014 paper and 2017 AES Berlin Tutorial T5, also his comments posted to the reflector earlier in the day.
J Paul volunteered to produce revised drafts (with changes tracked) by March 2018, for consideration first by the Secretariat and then by the Working Group.
AES5-R: Review of AES5-2008 (r2013): AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
This needs to be revised, reaffirmed, or stabilised in 2018. K Gross suggested that sampling frequencies that are no longer in common use should be deprecated, and volunteered to draft a revised text.
AES10-R: Review of AES10-2008: AES Recommended Practice for Digital Audio Engineering - Serial Multichannel Audio Digital Interface (MADI)
and AES-10id-R Review of AES-10id-2005 (r2011): AES information document for digital audio engineering - Engineering guidelines for the multichannel audio digital interface (MADI) AES10
and AES-X213: MADI over twisted-pair cabling
M Brunke is still working on the revised text. Task group SC-02-02-L and project AES-X213 to be closed, with the work moving into SC-02-02-M and AES10-R.
AES53-R, Review of AES53-2006 (r2011), AES Standard for digital audio - Digital input-output interfacing - Sample-accurate timing in AES47
Following further discussion on the reflector, some further revisions were made to the text. There have been no objections to the latest draft as amended by the e-mail from J Fletcher of 19th September.
AES41-x-R Review of AES41-x-2012: AES standard for digital audio - Audio-embedded metadata (all five parts) AES55-R, Review of AES55-2012: AES standard for digital audio engineering - Carriage of MPEG Surround in an AES3 bitstream
Reaffirmation of these six standards was approved by the WG at the end of September. Nothing further was proposed at the meeting.
Old projects:
AES-R4-R: Review of AES-R4 2007: Guidelines for AES standard for digital audio - Digital input-output interfacing - Transmission of digital audio over asynchronous transfer mode (ATM) networks, AES47 AES-R6-R: Review of AES-R6-2011, Guidelines for AES50 (HRMAI)
These reports should be stabilised, because they are companion documents to standards that have been stabilised.
Liaisons:
J Yoshio reported that the stability date for IEC 60958-4 (which mirrors AES3) is at the end of 2018. A new Part, 60958-5, specifies a physical layer to carry up to 32 channels for consumer use.<
P Treleaven proposed that in future agendas there should be separate items for (1) formal liaisons and (2) informal reports of activity in other fora.
New projects
No new projects were proposed.
New business
DSD over PCM (DoP) is becoming popular, and may become an appropriate subject for standardisation in AES.
The meeting closed at 15:30.
The next meeting will be scheduled in conjunction with the AES 144th Convention, to be held 23 to 26 May 2018 in Milan, Italy.
