SC-02-02 meeting, San Francisco, 2010-10

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 San Francisco, CA., US., 2010-11-04.

The meeting was convened by vice-chair S. Lyman.

The agenda, noting three topics to be handled under Other Business, was approved. The report of previous meeting, held in London, UK., 2010-05, was approved.

Open Projects

NOTE Unless stated otherwise, the status of open review projects is, "No action requested or required".

AES41-R Review of AES41-2009: AES standard for digital audio - Recoding data set for audio bit-rate reduction
AES41-2009 was published 2010-07-06. Additional metadata sets have been added to AES41 sinces its first publication. The proposed addition of yet more metadata sets moves the use of AES41 further from its orginal intent than appears appropriate.

It is therefore proposed to consider either revising AES41 and dividing it into a generic transport mechanism and separate descriptions of sets of metadata that may be carried by the transport mechanism, or by producing a new standard along similar lines.

The existence of other "transport" and "data to be transported" standards (for example IEC 61937, SMPTE 337, AES52) is acknowledged and will be taken into account when defining the metadata set formats and transport mechanism.

It is anticipated that the transport mechanism from AES41 may be used "as is", or with the adoption of a different synchronisation preamble to reduce the burden of maintaining compatibility with AES41-2009.

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
scope: to set a standard practice for mapping multiple channels of audio in linear PCM or AES3 format into an ATM transport system, for the purposes of interconnecting large numbers of sources and destinations, with best performance for latency, jitter and other relevant factors.

Please review for possible action in 2011

AES50-R Review of AES50-2005, AES standard for digital audio engineering - High-resolution multi-channel audio interconnection (HRMAI)
Scope: To specify a bi-directional, point-to-point connection for up to 48 channels of digital audio in a variety of formats. The link uses a single Category 5 (or better) structured-wiring data cable, and is designed for use in a studio environment. The system uses the 100Base-TX physical layer of Fast Ethernet (IEEE 802.3) to transfer framed audio data. Audio synchronisation is maintained by transmitting an audio clock signal in parallel with the audio data utilising available signal pairs on the cable.

The current draft is ready for final PWD to include corrections prior to PCFC

AES51-R Review of AES51-2006: AES standard for digital audio - Digital input-output interfacing - Transmission of ATM cells over Ethernet physical layer
Scope: Specifies an encapsulation of ATM cells in Ethernet packets, so that ATM equipment may be connected using hardware specified for Ethernet networks.

Please review for possible action in 2011

AES52-R Review of AES52-2006, AES standard for digital audio engineering - Insertion of unique identifiers into the AES3 transport stream
scope: This standard specifies the method for inserting unique identifiers into the user data area of an AES3 stream. This specifically covers the use of UUID as well as a basic or extended SMPTE UMID.

Please review for possible action in 2011

AES53-R Review of AES53-2006, AES Standard for digital audio - Digital input-output interfacing - Sample-accurate timing in AES47
scope: This standard specifies how the timing markers specified in and 4.5 of AES47 may be used to associate an absolute timestamp with individual audio samples. It does not specify how the recipient of a call is informed whether the timing markers will conform to this standard or merely meet the minimum specifications laid down in AES47.

Please review for possible action in 2011

AES-2id-R Review of AES-2id-2006: AES information document for digital audio engineering - Guidelines for the use of the AES3 interface
scope: to present information intended to assist a user to understand and use the AES3 digital audio interface. The document covers four basic topics: general, operational, electrical, and troubleshooting. Please review for possible action in 2011

AES-10id-R Review of AES-10id-2005: AES information document for digital audio engineering - Engineering guidelines for the multichannel audio digital interface (MADI) AES10
scope: to provide guidance for areas of application of the MADI standard (AES10) that might be unclear. The information presented in these guidelines is not part of the AES10 standard. It is intended to assist a user to understand and use the MADI interface. The AESSC hopes these guidelines will further the design of mutually compatible interfaces and encourage consistent operational practices.

Propose to reaffirm this document.

AES-R6 Guidelines for AES50 (HRMAI)
scope: Guidelines for AES50, High-resolution multi-channel audio interconnection (HRMAI)

Current draft ready for final PWD.

Development projects

AES-X139 Liaison with EBU ECA-Audio
A. Mason reported. The work of P/Loud continues. EBU Recommendation R128 (Loudness normalisation and permitted maximum level of audio signals) has been published; T3341 ('EBU Mode' metering to supplement EBU R 128 loudness normalisation), T3342 (Loudness range: A descriptor to supplement EBU R 128 loudness) are also available. T3343 and T3344 distribution and production guidelines are expected to be available soon.

ECA-BWF is working on revisions of its Broadcast Wave format to include loudness metadata. A revision of the MUSHRA test is planned to include a new anchor element.

AES-X182 AES/Ethernet Simple Open Protocol
scope: to specify a means for transmission over category 5 data cable of unidirectional digital audio and bidirectional control data. Intended applications are active loudspeakers and amplifiers for live performance and for installations.

Drafts of the proposed standard and its companion document have been posted to the working group document site in the past several days. Working-group members are asked to review it and comment as soon as possible.

AES-X186A Liaison with ITU-R re BS.1873, derived from AES10-2008 (MADI)
scope: Liaison with ITU-R WP6B to ratify text of AES10-2008 with restrictions on sampling frequency.

No action requested or required

AES-X186B Liaison with ITU-R re draft BS.647, derived from AES3-2009
scope: Liaison with ITU-R WP6B to update text of AES3-2009 for broadcasting.

K. Hamasaki reported that a revised BS.647 has been approved by the group - publication pending 3-months comment from ITU members.

AES-X186C Liaison with ITU-R re draft BS.[sync], derived from AES11 SC-02-02
scope: Liaison with ITU-R WP6B to update text of AES11-2009 for broadcasting.

ITU-R Rapporteur will study audio and video synchronisation.


SMPTE Time Related Labels
P. Treleaven reported that the SMPTE 33TS Time Related Label group had a question regarding the capacity of AES3 to carry time-related data to support the emerging SMTE work on audio/video synchronisation. It has been suggested that the whole of the user-data capacity could be dedicated to this use. The meeting felt strongly that conflict with other uses of the User Data space should be avoided and pointed out that a mechanism for carrying streamed metadata already existed in AES52-2006. Although this standard is described as a vehicle for unique identifiers, a registration scheme (6.3, table 1) provides for many types of metadata.

New Projects

8-channel digital audio interface
A. Mason raised a potential project for an 8-channel digital audio multiplex based on AES3 operating at quadruple frame rate. This would be used for a) multichannel equipment interconnections for television, and b) multi-channel digitally-interfaced microphones as an extension of AES42. There was general support in the meeting for this idea.

Considerations already identified include whether this should be achieved by modifications to the meaning of channel status bits (for example in byte 1 or byte 3) to signal a different usage mode of AES3; how existing equipment might respond to signals in this new format, whether damage to tweeters is possible during a switched transition between streams, and whether the effects can be reduced by choice of signalling. The effects of switching between signals in this mode (caused, for example, by incomplete channel status blocks) will also be thought about.

There will need to be consideration of the required behaviour of equipment that could act as "multiplexers", combining 4 conventional two-channel AES3 interfaces into 1 quadruple-rate interface. Account also needs to be taken of the fact that there is channel status data for the two subframes on the interface, both on the incoming signals to be multiplexed, and the output. The definition of channel mappings for the 8 channels (for example, "L, R, C, LFE, Ls, Rs, Lt, Rt") will also be considered to decide whether this belongs in the revision or should be left undefined. Existing channel-mapping standards are already known from SMPTE, ITU, EBU, and will be considered.

The question of whether this proposal is best realised by a revision to AES3 or by creation of a new standard was discussed. The Standards manager felt that it should be developed in an independent project in any case and the choice of publication mode would be clear by the time of the final draft.

A project initiation is expected from A. Mason and initial task group to include Lyman, C. Chambers, and K. Gross with Mason as TG leader.

New Business

There was no new business.

The next meeting will be held in conjunction with the AES 130th Convention in London, UK.

AES - Audio Engineering Society