Report of the meeting of Working group SC-02-01 on Digital Audio Measurement of the SC-02 Subcommittee on Digital Audio, held at the AES 117th Convention in San Francisco, 2004-10-29.
The meeting was convened by chair by S. Harris.
The agenda and the report of the previous meeting were agreed as written.
Open projects:
AES-6id Personal computer audio quality measurements
W. Jones has extensively revised the document and a PTD was recently posted on the SC-02-01 document site. Jones led a discussion through the major points of the revised draft. He commented that Microsoft WHQL has a new audio quality document, which sets the requirements for next-generation personal computers (PCs). It was felt that the document in IEC project 61606-4 Audio and audiovisual equipment - Digital audio parts - Basic measurements methods of audio characteristics - Part 4: Personal computer should be consistent with the new revision of AES-6id, and vice versa.
M. Furukawa made some suggestions.
IEC 61606 uses -20dB as a reference level for many measurements and it would be useful if AES-6id could be consistent with this. Check on the crosstalk definition, the input of channel under test should be ground, rather than output. For channels which use 10 bits or less, it would be better to use -30 dB as a test level rather than -60 dB for measuring dynamic range.
The question was asked whether the definition of a PC included a PC with an external audio break-out box? For the purposes of AES-6id, yes. For IEC 61606-4, probably not.
Furukawa said that he would report test data for Sony, JVC, and other PCs the following day at the IEC 61606 meeting
It was recognised that Jones could to contribute usefully as an expert in the IEC 61606-4 project group, and this could be an effective coduit for comments from the AESSC group. Jones and M. Yonge will investigate how to expedite this through the US National Committee. J. Yoshio offered to send the name of an appropriate contact person.
An updated AES-6id PTD will be posted by Jones by 2004-11-12 for review. The timing of the final publication of AES-6id should be aligned with the timing of IEC 61606-4 so we can make sure that both documents are consistent.
AES17-R Measurement of digital audio equipment
I. Dennis is revising the document and it is hoped that this could be aligned with the new IEC 61606-3 Audio and audiovisual equipment - Digital audio parts - Basic measurements methods of audio characteristics - Part 3: Professional use. A PTD will be finished before the Barcelona convention.
The timing of the release of AES17-R should be aligned with timing of IEC 61606-3, so they can be made consistent as far as possible.
Development Projects
AES-X102 Liaison with IEC PT 61606
Dennis reported that IEC 61606 meeting on 2004-10-30 will discuss 61606-3 (similar to AES17) and 61606-4 (similar to AES-6id) - see above. Dennis has suggested changes to IEC 61606-3 to bring it into line with AES17.
AES-X118 ITU-R study group 6 liaison
Several documents on loudness have been forwarded to the group in the last six months for members' information.
AES-X141 Accurate measurement and indication of peak signal levels to avoid overload of digital media.
M. Keyhl has posted an outline report for study by the committee. C. Todd (convenor of ITU-R 6P/SRG3) made some comments during the meeting. The use of this peak level indicator is intended for broadcast channel use and not for CD level mastering. In Section 3, Method B "Headroom Prediction": Todd said that this is not a necessary part of the brief for ITU. Since the downstream processing is unknown, we can not predict or allow for the effects of that processing. He felt that Method "A" and Figure 1b were good. It was noted that the purpose of the emphasis filter is to force the use of more headroom at high frequencies. It is necessary to specify what the emphasis should be. It is also necessary to specify what the upsampling ratio should be; for example, would a factor of two be satisfactory?
Craig will post early feedback on Keyhl's document after the ITU-R meeting next week. Keyhl was requested to edit the current document to take into account the feedback from this meeting and also from Todd next week, and to issue a new version by the end of February 2005. This will allow time for committee comments before the following ITU-R meeting on 2005-04-06.
Todd raised a new issue about setting a nominal level for broadcasters to use so that different sources are heard at the same volume. This is just a discussion point at the moment.
AES-X151 Jitter performance specification
A new PTD was posted by Travis in 2004-10. Travis proceeded to discuss the PTD in some detail. The text is similar to the AES paper presented on 2004-10-30.
S. Sohma indicated that surround sound systems are more sensitive to clock jitter than mono or stereo. He suggested that some liaison with SMPTE might be useful, however S. Lyman indicated that no work was currently happening in SMPTE on jitter audibility and that SMPTE would look to AES to provide the expertise in this area.
There was some discussion about including interface jitter information from AES3 and AES-2id in this information document, without conclusion.
The secretariat will format the Travis PTD as an AES Information Document by 2004-12-31. At the same time, the committee members will review the PTD content. The goal is to issue a PWD in January or February 2005.
New Projects
No new projects were proposed.
New Business
There was no new business.
The next meeting is scheduled to be held in conjunction wih the AES 118th Convention in Barcelona, Spain, 2005-05.
