Report of the SC-02-02 Working Group on Digital Input/Output Interfacing of the SC-02 Subcommittee on Digital Audio meeting, held in conjunction with the AES 112th Convention in Munich on 8th May 2002
The meeting was convened by J Nunn, Chair of the AES Standards Committee.
The agenda and the report of the previous meeting were approved as written.
Current Projects
AES-2id-R Review AES-2id - Guidelines for the use of AES3 interface
No action was taken
AES-3id -R Review of AES-3id - Transmission of AES3 formatted data by unbalanced coaxial cable
No action was taken
AES-10id-R Review of AES-10id - Engineering guidelines for the multichannel audio digital interface (MADI) AES10
This document will be reviewed following completion of AES10-R.
AES3-R Revision of AES3 - Serial transmission format for two-channel linearly represented digital audio data
Secretariat to check that the current PWD incorporates all necessary style changes. The revision of the general circuit configuration (figure 6 of AES3-1992) was agreed following notification on the email reflector. The new figure 6 has been sent to IEC MT60958-4 and it is expected that it will be incorporated in the revision of IEC 60958-4.
J Brown submitted a paper, which was the output of a small writing group, containing the revised figure 6 along with two alternative sets of notes. After some discussion it was felt the first set of notes was too long and too prescriptive for inclusion in the standard itself and should instead be incorporated in a revision of AES-2id. It was agreed that the second, simpler, set of notes should be accompany the diagram in AES3-R.
It was noted that clause 6.1 needs to be reworded to reflect the changes to figure 6. In particular, since figure 6 has been made more general, paragraph two of clause 6.1 is no longer correct as the diagram no longer gives information to improve the balance. In addition, the third paragraph in clause 6.1 refers to series capacitors which are no longer shown. The last sentence in this paragraph contains a 'shall' clause relating to equalisation which needs to be retained.
A target date of mid-June was agreed for the PWD.
AES10-R Review of AES10 - Serial multichannel audio digital interface (MADI)
Based upon email discussion on the working group reflector, R Caine was of the opinion that the necessary information had been passed to the Secretariat to enable a PCFC to be written. It was agreed that clause 7.1.5 should be deleted, in clause 7.1.4 the second sentence should be deleted to avoid conflict with clause 7.1.7 and clause 7.1.3 should be reworded in line with Robin Caine's email of 2nd April giving the attenuation in the form '10dB/100m'.
A new PCFC is expected at the end of May 2002. CFC anticipated in mid July allowing two weeks for the working group to consider to document.
AES18-R Review of -- Format for the user data channel of the AES digital audio interface
There were no comments on the CFC and the standard has now been re-affirmed.
AES41-R Review of AES41 -- Recoding data set for audio bit-rate reduction
No action was taken.
AES47-R Review of AES47 - Digital input-output interfacing - Transmission of asynchronous transfer mode (ATM) networks
The standard was published in April along with a guidelines report, AES-4R.
C Chambers informed the meeting about a development at the BBC using routing equipment employing the AES47 standard. The test set up is a 40x40 switch providing point to point, or point to multi-point, routing for audio streams over standard infrastructure cabling. The system also supports different sampling frequencies simultaneously.
J Grant and Chambers raised the issue of 'end point references'. In the case where a source is routed to a number of destinations, each destination has an end point reference. When a single route is removed it is important that the end point reference becomes free for further use and that other routes made from the same source are unaffected. Grant did not feel that it would be necessary to modify AES47 but some clarification could be included in the Guidelines AES-R4. This issue really relates to the control structure for such networks and in the case of AES47 this was deliberately kept simple so as to be adequate but no more than adequate.
AES-X50 Guidelines for Development of Specifications Which Reference or Use AES3 Formatted Data.
This project is suspended pending the availability of effort.
AES-X94 Presto: audio via synchronous digital hierarchy (SDH)
This project is suspended pending the availability of effort. The project will be reviewed again at the next meeting in Los Angeles. Unless there is some indication that progress can be made then it is likely the project will be terminated.
AES-X111 Transmission of the unique material identifier (UMID) on AES3.
Chambers apologised for the delay in progressing this project which was partly due to continuing discussion within SMPTE on the way the UMID was going to be used. Chambers felt the UMID clearly needs to be contained within the channel data stream and he felt that channel status was the place for it to be carried. One proposal was to use Byte 5 for UMID data and bit 2 of Byte 4 as a start of UMID flag which would give one basic UMID of 32 bytes every 64 frames. Another idea was to use the Key-Length-Value (KLV) technique to reduce the payload. It was felt that if the UMID could be made to fit one block then the User channel would be a suitable place for the UMID.
Chambers said he would submit a proposal for discussion on the Task Group G reflector within four weeks.
AES-X119 Connector for AES3 interfaces
Brown reported on task group discussions. The task group seems to be unconvinced about the need for another connector and there had been some discussion on the issue of cross-talk between analogue and digital audio circuits. Brown was in favour of a separate connector to differentiate between analogue and digital circuits. Nunn pointed out that this was not the purpose of the task group, the issue was one of damage to equipment if digitally interfaced or analogue microphones are incorrectly connected. The XLD connector has been proposed as a solution to this problem and the issue is whether or not to include the XLD in the AES3 standard.
Caine stressed the need for SC-02-02 to focus on need to determine whether the use of the XLD connector is rejected, made optional or made mandatory in AES3. J Woodgate was of the opinion that the XLD provided a useful migration path to a separate digital connector for those users and manufacturers that wished to change. He also suggested a guidance document would be useful so that the various issues could be explained. Those present felt AES-2id would be a suitable place for this information.
The working group felt that the XLD should be made the 'preferred' option, however, Brown was asked to consider all the options (as set out in the report of the previous meeting) in the task group and report back to the working group. Brown agreed to try to report back by the end of July. The task group will need to propose the wording for an amendment to AES3 if this is necessary and to draft suitable guidance notes for inclusion in ASE-2id.
New Projects
No new project requests were received or introduced.
New Business
There was no new business.
Liaison
It was noted that IEC groups MT 60958-1 and MT60958-4 were due to meet during the convention. The Convenor for IEC MT60958-1 informed the meeting that the revision of 60958-1 was now at the CD stage after tomorrow's meeting it will progress to a CDP for voting. The Japanese Committee have submitted a proposal for the inclusion of an optical connector for consumer use. There are two alternative proposals, in one the optical connector is included in 60958-3 (preferred by the Japanese Committee) and in the other it is included in 60958-1. Members of SC-02-02 were invited to the MT60958-1 meeting as observers.
Nunn informed the meeting that the EBU has set up a new group for audio, P/AGA, Advisory Group on Audio under the chairmanship of J Emmett. This group replaces earlier groups dealing with audio and it covers a very broad range of topics including multichannel audio, ATM, digital interfaces, BWF developments, loudness metering, etc. The group will be holding a meeting during the convention so as to maintain liaison with the AES.
Date of Next Meeting
The next meeting is scheduled to be held in conjunction with the AES 113th Convention in Los Angeles, CA, US.
