Audio Engineering Society Standards Committee

May 2001 report of SC-02-02

[Last printing 18 September 2001] 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 110th Convention in Amsterdam, The Netherlands, 2001-05-10

Chair J. Dunn convened the meeting. The agenda were approved with the addition of two liaison items: SC-05-05 over project AES-X13 and IEC MT60958-x over maintenance of IEC60 958-1. The report from the previous meeting was approved as written.

Current development projects

AES-2id-R Review of AES-2id-1996 AES information document for digital audio engineering -- Guidelines for the use of the AES3 interface

The CFC for reaffirmation completed its comment period with no objections. There was no further action by the group.

AES-3id-R Review of AES-3id-1995 AES information document for digital audio engineering -- Transmission of AES3 formatted data by unbalanced coaxial cable

No comments on the CFC for revision had been received prior to the meeting.

AES-10id-R Review of AES-10id-1995 AES information document for digital audio engineering -- Engineering guidelines for the multichannel audio digital interface (MADI) AES10

No technical changes were proposed. The WG is not considering this document until the new edition of AES10 has been completed.

AES3-R Revision of AES3-1992 (r1997) AES Recommended practice for digital audio engineering -- Serial transmission format for two channel linearly represented digital audio data

It was agreed that more liaison should take place between SC-05-05 and SC-02-02. J. Nunn suggested that cross-membership of the reflector was the appropriate mechanism. Brown will clarify at the SC-05-05 meeting whether digital interconnects are within the scope of project AES-X13.

AES10-R Review of AES10-1991 (r1997) AES recommended practice for digital audio engineering -- Serial multichannel audio digital interface (MADI)

C. Travis will draft an answer to the comment on 7.1.5 by V. Recipon.

The comment affects specifications of cable length and equalization. The working group decided that a change was appropriate to indicate that the intention of the subclause is to indicate the transmission distance without the need for equalization to be expected with equipment that meets the specifications for cable, driver, and receiver. However receiver equalization was not intended to be forbidden. Transmitter equalization was already prohibited by the specification for transmitted pulse shape.

Travis will prepare wording that improves the text of the clause so that it is unambiguously correct but without making a substantive change.

AES18-R Review of AES18-1996 AES recommended practice for digital audio engineering -- Format for the user data channel of the AES digital audio interface

No proposals for changes to this document were made. SC-02 will be asked to reaffirm the standard.

AES41-R Review of AES41-2000 AES standard for digital audio engineering - Recoding data set for audio bit-rate reduction

This document was published in 2000. No proposals for changes to this document were made.

AES-X50 Guidelines for Development of Specifications Which Reference or Use AES3 Formatted Data

No work had been done on this project since the last meeting. Suspension will be requested subject to review of its status 2001-09.

AES-X92 Digital Audio in asynchronous transfer mode (ATM)

Specific questions will be posted to the SC-02-02-E task group reflector 2001-05 by J. Grant. M. Yonge, the task group leader, plans to hold a meeting 2001-06 to prepare a PTD by 2001-08 so that a PWD can be ready 2001-09. The group hopes to have a PCFC 2001-10.

The WG discussed the notes (X92-JG-NOTES2-010331.PDF) to the PTD (X92-JG-PTD2-010331.PDF) which had been posted to the task group (SC-02-02-E) by Grant.

Yonge asked the WG to consider 4 questions:
1) Was a 32 bit audio sample word length ever required to be supported as the largest length?
2) When packing sample data into cells, should the data be grouped by channel or with co-sampled data together (temporal grouping)?
3) Should one or more sample rates be supported as a mandatory requirement?
4) Is synchronisation over long distances under consideration?

It was agreed that question four would be raised at the meeting of SC-02-05 later in the convention. [NOTE: Project AES-X121 has been initiated].

AES-X94 Presto: audio via synchronous digital hierarchy (SDH)

The group will request suspension of the project with a status review 2001-09.

AES-X111 Transmission of the universal media identifier (UMID) on AES3

C. Chambers will prepare the project initiation form as decided 2000-09. He proposed as a project description, "To establish the insertion method and transmission path of SMPTE UMID, as defined in SMPTE 330M-2000 Television Unique Material Identifier (UMID), through the AES3 interface. The specific issues that will be addressed in particular are the UMID symbol rate and UMID system transparency.

Travis suggested that the scope could be more general so that it extends beyond UMID. Dunn suggested that this might only be acceptable if it did not delay the work significantly.

Dunn asked if it is possible that all that is required of AES3 is that devices are transparent to the user data channel. If so, it may be possible that this work does not require any change to AES3. Therefore the project could produce another standard or information document instead of an amendment to AES3.

Chambers agreed to post a PTD containing a requirements specification to the WG reflector. He will need to consult with N. Gilchrist to determine when this posting can be achieved.

AES-X119 Connector for AES3 interfaces

This project was initiated by S. Harris. He explained that the project to develop the standard AES42, Digital interface for microphones, in SC-04-04 had produced request to use a connector that has keys to avoid inadvertent mis-connection. These requests applied to AES42 but could be applied to other uses of AES3. AES42 uses the AES3 interface and so requires the use of the XLR. It also contains diagrams showing the XLD connector, a key version of the XLR. With the keys fitted, it will not connect to an XLR; but with the keys removed, it will freely interconnect with an XLR.

J. Brown explained why he felt that this was required now. This particularly concerns facilities for live performance where there are many tie lines with splitters to feed many destinations from one source. The XLD is preferred because it is retrofittable. Brown feels that it should be a requirement on new equipment.

There was discussion about the role of the new connector if it were introduced to AES3. Would it be permitted as an alternative to the main (XLR) connector? Would it be preferred to the XLR for new designs? Would it be required for new designs? Should the keys be required to be fitted as the connector is supplied?

Dunn explained his concern that the proposed connector had not yet been manufactured except as samples and that the industry has no experience with it. It should be incorporated into a standard before the industry experiences its use in real situations over an extended period.

Harris stated that it was his impression that the connector would not be made until a manufacturer saw it recommended by the AES standard. If that could not happen until it was made then it would never happen.

Task group SC-02-02-F was formed by Harris for the project. Harris will suggest modifications to the project scope. In his view, SC-02-02-F should not consider any connector other than the XLD.

New projects

No project requests were received or introduced.

New Business

Project AES-X13, assigned to SC-05-05, was discussed in connection with project AES3-R.

With regard to IEC TC100 maintenance of IEC60958-1 J. Yoshio presented a proposal for IEC60958-1 maintenance work. It seeks to add informative explanations for:

1) all of the IEC60958 families and their relationships;
2) CD-ROM data transmission;
3) validity bit usage;
4) the category code system.

This proposal is to be submitted to TC100 for consideration for the maintenance of IEC60958-1.

The next meeting is scheduled to be held in conjunction with the AES 111th Convention in New York, New York, US.

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