SC-02-02 meeting, Vienna, 2007-05-04

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 Vienna, Austria, 2007-05-04

The meeting was convened by chair J. Grant.

The agenda and report of the previous meeting, 2006-10-04, were accepted as written.

[The current scope and status of individual projects is listed at www.aes.org/standards/b_policies/project-status.cfm ]

Open Projects

AES-R4-R: Review of AES-R4 2002: Guidelines for AES standard for digital audio - Digital input-output interfacing - Transmission of digital audio over asynchronous transfer mode (ATM) networks, AES47
Grant reported that the new draft was uploaded and announced on the reflector on 4th April. There have been no comments on the reflector, and were none at the meeting.

The new text should be published.

AES-R6: Guidelines for AES50 (HRMAI) Project scope: Guidelines for AES50, High-resolution multi-channel audio interconnection (HRMAI)
M Page reported that he no longer works for the company that developed AES50, and would therefore not be able to contribute further. It is likely that within 6 to 12 months the technology would be owned by a company that wishes to develop it further.

No action requested or required.

AES-2id-R: Review of AES-2id-2006: AES information document for digital audio engineering - Guidelines for the use of the AES3 interface
R Caine reported that he already has a list of items which could be added to AES-2id, largely related to AES11. Also, this document will require revision when AES3 is restructured (see AES3-X).

No action requested or required at this stage.

AES-3id-R: Review of AES-3id-2001 (r2006): AES information document for digital audio engineering - Transmission of AES3 formatted data by unbalanced coaxial cable
Recently reaffirmed as AES-3id-2001 (r2006). No action requested or required.

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
No action requested or required.

AES3-R: Review of AES3-2003: AES standard for digital audio engineering - Serial transmission format for two channel linearly represented digital audio data
Maintenance of the current AES3-2003 is now separate from the project to restructure this complex document in layered form - see AES3-X.

Clarification that the standard does not apply in the case where Status Data bit 1 = 1 in byte 0 (similar to the case where bit 0 = 0) would be desirable. See also AES-X159.

AES3-X: Restructure of AES3-2003: AES standard for digital audio engineering - Serial transmission format for two channel linearly represented digital audio data
This document will specify, in layered multi-part form, a recommended interface for the serial digital transmission of two channels of periodically sampled and linearly represented digital audio data from one transmitter to one receiver.

Caine requested that when the CFC is issued it include a list of the substantive changes; that is, those areas where the technical specifications in the new standard are intentionally different from those in the old.

Caine to proceed with production of the final text.

AES5-R: Review of AES5-2003: AES recommended practice for professional digital audio - Preferred sampling frequencies for applications employing pulse-code modulation
No action requested or required.

AES10-R: Review of AES10-2003: AES Recommended Practice for Digital Audio Engineering - Serial Multichannel Audio Digital Interface (MADI)
No action requested or required.

AES11-R: Review of AES11-2003: AES Recommended Practice for Digital Audio Engineering - Synchronization of digital audio equipment in studio operations
No action requested or required.

AES18-R: Review of AES18-1996 (r2002): AES recommended practice for digital audio engineering - Format for the user data channel of the AES digital audio interface
No action requested or required

It was felt that his standard should be "frozen"; that is, continue to be available but no longer maintained.

AES41-R : Review of AES41-2000 (r2005): AES standard for digital audio - Recoding data set for audio bit-rate reduction
No action requested or required.

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
No action requested or required.

AES50-R: High Resolution Multichannel Audio Interconnection (HRMAI)
See discussion on AES-R6; amendment to be delayed until effort available.

AES51-R: Review of AES51-2006: AES standard for digital audio - Digital input-output interfacing - Transmission of ATM cells over Ethernet physical layer
No action requested or required.

AES52-R: Review of AES52-2006, Insertion of unique identifiers into the AES3 transport stream
No action requested or required.

AES53-R: Review of AES53-2006, Sample-accurate timing in AES47
No action requested or required.

Development Projects

AES-X121: Synchronisation of digital audio over wide areas
Grant reported that he has used a development of the current draft as the basis for text to be incorporated into an EBU document. M. Yonge suggested that a similar text would be appropriate as the final version of this report.

R Caine proposed using part of this report in AES-2id in the section on synchronisation and AES11, relating to a a paragraph on sync history

Grant to produce and circulate draft.

AES-X139: Liaison with EBU P/AGA
R. Chalmers reported that P/AGA met in December 2006 at BBC Kingswood Warren, but nothing of relevance to SC-02-02 was discussed.

AES-X159: Carriage of PCM with MPEG Surround data over AES3
J. Herre explained that the "surround" information is carried in the low bits of the stereo PCM samples, using a maximum of 5 bits and typically 3 or fewer, and is noise shaped as described in a paper presented at an AES convention in about 1995 so that audible artefacts will not appear in the signal if these bits are treated as the low bits of the sample. The surround information cannot be decoded if these bits are corrupted, for instance by re-dithering, sample rate conversion, or change in signal level.

The current draft specifies that bit 2 in byte 4 of channel status shall be set to 1 to indicate that the audio data contains information that would be destroyed by any processing of the audio signal. This bit has also been used to indicate DSD, but only when bit 1 of byte 0 is a 1.

There are two other amendments that could be made to AES3 at the same time. One is to define code points in bits 3-6 of byte 4 for 384 kHz and 352,8 kHz; the other is to specify what should be in the rest of Channel Status when bits 0 and 1 in byte 0 = "11". This last is less straightforward than the changes in byte 4.

Grant to propose text for the changes to byte 4 of channel status in AES3.

AES-X161: Digital interface for loudspeakers
A new work item in IEC TC100, document 100/1217/NP, proposes to send MIDI messages in the AES3 User data for the purpose of controlling a digitally-interfaced loudspeaker. When it is more advanced, a code point should be assigned in bits 4-7 of byte 1 in Channel Status (user bits management) to indicate "MIDI format data".

The existence of this IEC project does not affect the early stages of AES-X161.

S. Heinzmann undertook to talk to loudspeaker manufacturers.

Liaisons

For IEC TC100, J. Yoshio reported that:
  • IEC 60958-1 Ed. 3.0 is ready for CDV ballot, and the maintenance team is starting work on Ed. 4.0;
  • In 60958-3, loudness and channel assignment are to be added to Channel Status;
  • A new Part of IEC 61937 is planned to support MPEG4 ALS;
  • IEC MT61937 is studying general channel assignment models to support 27-channel DTS, 24-channel Dolby, and NHK's 22.2 format.
K. Hamasaki reported that NHK is planning to begin experimental "ultra high definition" TV transmission in 2011 and public service in 2025; the image is 7680 x 4320 pixels intended for a horizontal viewing angle of 100 degrees; sound is 22.2 including 9 speakers at high level and 3 front speakers + 2 LFE at low level.

Herre reported that MPEG is beginning work on the next generation of MPEG surround, and is continuing to work on coding such as low delay.

New Projects

No new projects were received or proposed.

New business

There was no new business.

The next meeting will be scheduled in conjunction with the AES 123rd Convention in New York, NY., US, 2007-10.

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