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., US., 2013-10-17
The meeting was convenened by chair J. Grant.
The agenda, and the report of the previous meeting, held in Rome, 2013-05-04, were approved as written.
AES3-x-R: Review of AES3-1-2009, AES standard for digital audio - Digital input-output interfacing - Serial transmission format for two-channel linearly represented digital audio data (four parts)
All four parts are due for reaffirmation, revision, etc, by next year, so this is the right time for WG members to post on the reflector any issues they think should be addressed by amendments. When doing so, please suggest new text wherever possible.
The action on the Secretariat and S. Heinzmann to review which fields of channel status should be modified when tunnelling through other transports (for Part 2) is still outstanding.
The proposal to add text to Part 4 to warn of jitter propagation when cascading links has been dropped, as no text has been forthcoming and it was thought this is less likely to be a problem in future installations.
AES5-R Review of AES5-2008: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
AES5 has been reaffirmed, which was necessary to prevent it timing out, but there is now a proposal to revise it at the same time that AES11 is revised (due by next year), to deprecate the use of 32kHz and to update the recommendations regarding sample rate conversion. K. Gross volunteered to prepare a proposed revised text.
AES11-R Review of AES11-2009: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations.
Some further changes to the current draft (aes11-r-130619-pwd-sec.doc) were suggested, including removal of 32kHz sampling from the tables and adding a note that where different sampling rates (such as 48 and 96 kHz) are used in a studio the digital audio reference signal (DARS) must be at the lower frequency because otherwise the phase at the lower rate is ambiguous. Other points raised included that in the newer SDI formats embedded audio doesn't have to be synchronised to the video, which has caused interoperability problems, and that AES67 needs AES11-quality clock distribution for studio use but Precision Time Protocol (PTP) is not necessarily accurate enough because the accuracy is not specified. S. Heinzmann volunteered to review the whole text of AES11 and prepare a revised text.
AES-R8: AES standards project report - Synchronisation of digital audio over wide areas
There was discussion at around the time of the previous Convention following a proposal from M. Law to revise the last paragraph (regarding quality of the timing reference), which segued into a discussion on modification of AES3 channel status. It had not been clear what change to AES-R8 was proposed, and the Chair volunteered to phone M. Law for clarification. [The outcome of the call was that the issue to be addressed is whether sample rate conversion needs to be in circuit at an input. Chair to propose text.]
Development Projects
AES-X182: AES/Ethernet Simple Open Protocol
The final TG draft has now been submitted to the WG for approval (x182-draft-zanghieri-130501.pdf in the WG document area).
AES-X186: Liaisons with ITU-R re BS.1873, BS.647, and BS.[sync], which are derived respectively from AES10, AES3, and AES11.
No further information had been received from ITU-R. [Note: ITU-R Recommendations may be downloaded from www.itu.int/pub/R-REC ; the current BS.1873 was published in 2010 and BS.647 in 2011; BS.[sync] was published as BS.2032 in 2013.]
AES-X196: Use of AES3 with high sampling rates to carry multi-channel audio
Tests by the BBC on how well each proposal works with existing equipment are still awaited. The meeting felt that the existing document, x196-bbc-proposal2-2012-06.pdf in the SC-02-02-K folder of the WG document area, gave (in 4.4 and 4.5) a good enough description of the two proposals that any implementations of them would be interoperable, so no further standardisation work was required until the outcome of the tests was known.
Secretariat to format the two schemes as an Information Document.
AES-X213: MADI over twisted-pair cabling
M. Brunke presented the new TG draft (x213-proposal-131017.pdf in the SC-02-02-L folder of the WG document area) which has no major technical changes; the technology has now been tested for conformance to IEEE 802.3. It is different from the Studer multichannel-over-Cat5 system, which is not compatible with AES10 (MADI).
K. Gross suggested that the description in 4.4.1 should be replaced by a normative reference to IEEE 802.3.
There was discussion whether the format, which does not include the IEEE 802.3 MAC header, could result in a switch interpreting the first six octets of a frame as a MAC address and filling its routing table with spurious entries if an X213 output is connected into one of its ports. M. Brunke pointed out that the MADI signals are not carried on the same pairs as standard Ethernet, so this could only be a problem if the site was wired to carry two 100BASE-TX connections on a single cable.
S. Heinzmann observed that X213 is described as bidirectional, whereas MADI is unidirectional, and suggested that advice on whether it is necessary to connect both directions (e.g. whether the Ethernet PHY chips require it) should be added.
Secretariat to format the draft as an amendment to AES10.
AES-X221: IEC 60958-4 Ed.3 revision
Secretariat's draft for the new edition of IEC 60958-4, in four sub-parts to match AES3, has been accepted by IEC TC100 TA4.
Liaisons:
J. Yoshio reported that IEC TC100 TA4 has completed edition 3.0 of 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 EBU loudness metadata. A new edition of IEC 61883-6, to which copy protection has been added, is in the final stages of approval for publication. An amendment to edition 2.0 of IEC 61937 to add clarification re AES3 audio is being prepared. TC100 now has a liaison with AVB (which is now called Time-Sensitive Networking), and an IEEE representative attended the recent TC100 meeting in Shenzhen.
New Projects:
No new projects were proposed
New Business:
K. Gross pointed out that there are now many ways to send audio over twisted-pair building wiring, including AES47, AES50, AES51, AES67, X182, and X213, and maybe a task group should be formed to rationalise the situation, making recommendations which should be used for different applications. M. Yonge said that, unlike many other standards groups, AES is not averse to standardising more than one solution to the same problem.
The next meeting will be held in conjunction with the 136th Convention in Berlin.
