Comments on DRAFT REVISED AES-2id-xxxx

last updated 2007-03-15

Comments to date on Comments on DRAFT REVISED AES-2id-xxxx, AES information document for digital audio engineering - Guidelines for the use of the AES3 interface,

was published 2006-12-28 for comment.

Comment received from Hirokazu Nakashima, 2007-02-26

Dear Yonge-san, I have 2 editorial comments to CFC on DRAFT REVISED AES-2id-xxxx.
  1. P.47 Annex A, Table A.1, line 9
    Byte Bit Function RX TX Remarks
    0 0 0 Consumer use N N
    ==> 0 0 0 Consumer use N N
  2. P.48 Annex B, B.2 BASIC program, line 10
    ==> c_status%(x%)=1
Please check it. Thank you.

Best regards,
Hirokazu Nakashima

Response from Mark Yonge, AES Standards manager, 2007-02-26

Dear Nakashima-san,

Many thanks for reading this draft so carefully. Because these are purely editorial issues, I can respond directly. I agree both your editorial corrections and I will incorporate them in the published document at the appropriate time.

best regards,

Mark Yonge
AES Standards Manager

Comment received from Jos Van Dyck, 2007-03-03

General Approach
Your suggestion to use separate documents for the various interface layers has been adopted by ISO and ITU-T for many years. It will require less standards maintenance when new transport technologies appear. The 7-layer ISO model allows for separate standards to describe physical layer (mechanical, electrical), protocol (data link, network, transport... application) layers, and actual data. The use of audio-specific standards should be avoided, in favor of existing telco (ITU-T), electrical (IEC) or computer standards (ISO).

For fixed installations, structured cabling systems (e.g. CAT 5, optical) are probably most convenient and economical to cary audio signals. More demanding installations could rely on Telco standards.

75-ohm coax connectors and cable
In Europe, Telcos use 75-ohm coax (ITU-T G.703) patch panels (distribution frames) and cabling inside central offices (E1/T1 and upwards). ETSI standard connector type is IEC 60169-13, impedance 75 Ohms (Type 1.6/5.6), with matching 75-Ohm coax cable (1.6/5.6 mm) specifically designed for demanding high-speed digital Telco transmissions (unlike RF coax for CATV or antenna cable). For several decades, these IEC 60169-13 connectors have proven to have better contact quality and are less prone to micro- interruptions compared to BNC plugs.

Best regards,
Jos Van Dyck, Consultant

Response from Robin Caine, Vice chair, SC-02, 2007-03-15

Dear Mr. Van Dyck,

Thank you for your comments on AES-2id and your encouragement on our choice of document structure. AES3 has grown over 21 years to it's present level of detail and we have found that revision became more and more difficult. The next revision is expected to be in four parts. AES-2id is only a guideline document and relies on the revision of AES3 as a multipart standard to achieve its OSI-like structure in a manner parallel to AES3.

The work on audio-specific standards is carried out specifically because audio (and video, and even more the combination of both) has requirements which are not addressed in generic digital standards, or are inadequately specified for high quality audio. Jitter performance affects sound quality by introducing intermodulation effects amongst others, and latency produces unworkable signals in a studio environment where mixing signals of uncertain relative delay can produce serious artifacts. Even a single sample difference in relative timing changes the frequency response of a mixed signal.

New standards are appearing in order to exploit the physical and datalink levels of computer interfaces (IEEE1394, later Ethernet, etc.) in which latency, jitter, and synchronisation are specifically addressed in order to maintain high quality audio standards while taking advantage of very cost-effective silicon parts.

Cat5 cable did not exist when AES3-1985 appeared, and the use of structured wiring has since been accepted by the standard, while pointing out the inconsistency between the screened cabling requirement of AES3 and the optional screening of structured wiring. In the late 1980s AES10, AKA 'MADI', exploited the provisions of FDDI for longer haul multichannel transmission (including fibre links) while maintaining the accuracy of AES3. The carriage of AES3 over Gxxx PDH carriers has been addressed by BBC Research resulting in standards at (if I recall correctly) CCITT, now ITU-T.

The use of 75-Ohm cable and the BNC connector in AES-3id was mandated by broadcasters with large installations wired with such cable and connectors for analogue video. I personally prefer the connector you refer to (is this also known as BT34?), but this is uncommon in television areas.

I hope this explains our position on AES-2id.
Robin Caine

AES - Audio Engineering Society