Report of the meeting of SC-02-02 Working Group on digital input/output interfacing of the SC-02 Subcommittee on Digital Audio, held in Amsterdam, 2008-05-16
The meeting was convened by chair J. Grant.
The agenda and report of the previous meeting, 2007-10-04, were accepted as written.
AES3-R: Review of AES3-2003: AES standard for digital audio engineering - Serial transmission format for two channel linearly represented digital audio data
A further amendment (Am.6) to AES3-2003 was proposed to introduce two changes before the restructuring and revision of AES3-X (below).
The first change is to withdraw the "minimum" implementation of Channel Status (7.2.1). The current text of AES3-2003 recommends not using this level, and points out that some receivers do not support it. The change would mean that transmitters implementing this level (which has been discouraged for many years) would no longer conform, but the receivers that do not support it would now conform.
The second change is to add code point 0110 "reserved for IEC 62537" to byte 1 bits 4 to 7 (see AES-X161).
AES3-X: Restructure of AES3-2003: AES standard for digital audio engineering - Serial transmission format for two channel linearly represented digital audio data
There was no support for changing the bit order in the tables in 5.5 of Part 2 so the most-significant bit is on the left (as in standard numeric notation). R. Caine will add a note clarifying that Byte 4, bits 0 to 1, are to be set to 00 for any signal that is not a DARS (Digital Audio Reference Signal). Also in Part 4, Table B.2, will update a note regarding the scaling of the jitter limits for higher sampling frequencies.
The draft can then go to PWD after incorporating changes suggested on the reflector (apart from reversing bit order in tables), and adding a recommendation to read AES-2id in the Introduction.
It was felt that AES3-X should not make any technical changes to AES3-2003. The straightforward changes should be in the proposed Amendment 6 to AES3-2003. After the restructured form is published, a task group should be set up to review the specifications for jitter and other issues related to higher sampling frequencies.
AES5-R: Review of AES5-2003: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
It is proposed to revise this standard by adding a new subclause specifying "octuple rate" after 5.3.4, and reviewing 5.2.5 in which the word "factor" seems wrong (Grant to propose new wording). See also AES11-R.
AES10-R: Review of AES10-2003: AES Recommended Practice for Digital Audio Engineering - Serial Multichannel Audio Digital Interface (MADI)
It is proposed to revise this standard by:
redrafting 4.1 and 5.1 to support double, quadruple, and octuple rates;
moving link transmission-rate tolerance from Annex A Note 1 (which is informative) to 5.2 (where it will become normative);
removing "Society of ... Broadcasting Union" from 6.1;
redrafting the last paragraph of 6.1 to recommend always using the basic rate sampling frequency for synchronisation, referring to 4.2.1 of AES11.
AES11-R: Review of AES11-2003: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations
It is proposed to revise this standard by:
adding a column for a frame rate of 24/1.001 to Table 1, and adding a note that "frame rates twice and four times those shown are also used" to cover 50 Hz etc;
moving tolerances currently in AES5 (e.g. 5.1 and 5.2.3) into AES11
M. Yonge will prepare a draft.
AES47-R: Review of AES47-2006: AES standard for digital audio - Digital input-output interfacing - Transmission of digital audio over asynchronous transfer mode (ATM) networks
J Grant to check status of amendment to 6.1.3 previously proposed to complement AES53-2006.
AES50-R: Review of AES50-2005, High Resolution Multichannel Audio Interconnection (HRMAI)
Chair to contact J. Oakley of Klark Teknik to enquire what maintenance required.
Development projects
AES-X121: Synchronisation of digital audio over wide areas
Proposed to retire this project as its work is done. AES-R8-2007 is now published.
AES-X159: Carriage of PCM with MPEG Surround data over AES3
Proposed to retire this project as its work is done. AES55-2008 is now published.
AES-X161: Digital interface for loudspeakers
the interface is being standardised as IEC 62537; there has been no recent progress on the collection of use cases.
AES-X180: Amendment to AES3-R, non-audio status clarification
Proposed to retire this project as its work is done. Amendment 5 to AES3-2003 is now published.
Liaison matters:
AES-X139: Liaison with EBU P/AGA
EBU P/AGA met at the same time as SC-02-02. R. Chalmers reported that none of the items on their agenda were especially relevant to SC-02-02's current projects. Mostly they are studying lip sync, also loudness and levels.
Liaison with IEC 60958
J. Yoshio and K. Hamasaki reported that IEC 60958-3 is to support a new satellite HDTV broadcast scheme with linear 5.1 encoded using SMPTE 302M (AES3 in MPEG transport), carrying downmix coefficients etc. in the User bits for which they are defining a new category code. Also, a data stream at 1536 kb/s is being defined for Dolby/DTS.
Also, a new IEC project, IEC 62574, on channel assignment of multi-channel audio, has been started. The IEC project on AV synchronisation (lip sync) needs harmonisation between professional and consumer versions.
New Projects
U. Zanghieri presented a scheme for carrying AES3 signals on the "spare" pairs (4-5 and 7-8) of Ethernet 100Base-TX in a system where an audio source and a number of destination devices (such as powered loudspeakers) are connected in a ring, so that the system can survive loss of any one of the links. The Ethernet connection is used purely for control, as the latency through each unit is much higher than on the AES3 connection. A Project Initiation Request will be submitted in due course.
C. Chambers suggested that transmission of audio over Next Generation SDH (NG-SDH) should be standardised.
New business
There was no new business.
The next meeting will be scheduled in conjunction with the AES 125th Convention in San Francisco, CA., US., 2008-10
