Report of the the meeting of the SC-02-01 Working Group on Digital Audio Measurement Techniques of the SC-02 Subcommittee on Digital Audio, held in San Francisco, USA, 2010-11-06
The meeting was convened by chair S. Harris.
The agenda and the report of the previous meeting, held in New York, 2010-05-24, was approved.
Scope of SC-02-01 reviewed
The scope of the SC-02-01 Working Group on Digital Audio Measurements currently reads: "measurement methods for equipment used for the recording, reproduction, and transmission of digital audio signals within the scope of SC-02. It includes effects of perceptually based coding algorithms on audio signals within the scope of SC-02. It includes psychophysical and electrical analysis under all operational and listening conditions. It includes ranking of codecs and test methods to determine presence of coders or their proper operation."
It was noted that AES17 is focussed on audio signal measurements, not specifically AES3 signals. AES17 also does not include the method of making the measurement, so actual implementation could be analog or digital.
Open Projects
AES-6id-R Review of AES-6id-2006: AES information document for digital audio - Personal computer audio quality measurements
This document is due for review in 2011. If anyone wishes to propose any revisions for this document, please send them to the email reflector. If there are no comments, AES 6id will be re-affirmed in 2011.
AES-12id-R Review of AES-12id-2006: AES information document for digital audio measurements - Jitter performance specifications
M. Yonge will check into updating references to AES-2id.
This document is due for review in 2011. If anyone wishes to propose any revisions for this document, please send them to the email reflector. If there are no comments, AES-12id will be re-affirmed in 2011.
There was a discussion about of "witter", a combination of jitter and wander. R. Caine and C. Chambers are writing a document about "witter", mentioned in SC-02-02. It may include some guidelines about what equipment should do, and under what conditions equipment should indicate loss of lock. A paragraph about witter could be included into a revision of AES-12id.
AES17-R Measurement of digital audio equipment
The current version has been reaffirmed. A new version is being created, see later development projects AES-X187A, and AES-X187B.
Development Projects
AES-X102 Liaison with IEC PT61606
Some history. IEC 61606, "Audio and audiovisual equipment - Digital audio parts - Basic measurements methods of audio characteristics" has four parts:
Part 1 - General
Part 2 - Consumer Use
Part 3 - Professional Use. This group (I. Dennis in particular) strongly influenced this.
Part 4 - Personal Computer
Part 4 was reconfirmed in June 2010, and the next review is due in 2013. We discussed sending AES-6id to IEC for information, but we decided that since Part 4 has just been reconfirmed there was no point in doing this.
The project leader for IEC 61606 has changed from Mr. Masamichi Furukawa, who has retired, to Mr. Hiroshi Furukawa (no relation).
AES-X118 Liaison with ITU-R Study Group 6C
A. Mason reported. This group produced BS.1770 loudness algorithm. A gating scheme has been introduced recently in order to address the disproportionate effect of silence on measured loudness. Loudness is first calculated without gating. A threshold is determined, then loudness is recalculated, This is called relative threshold approach. Many values of the threshold were proposed, from -8dB to -20dB. The value was fixed at -10dB. This was judged as a significant achievement.
The revised BS.1770 document was approved in its group in October 2010, there is a 3-month window for objections.
The Low Frequency Effects (LFE) channel is not measured today. There was a discussion about including the LFE channel in loudness measurements. There were also discussions about updating BS.1771 about integration times, scales, precision and units.
Loudness Range (variations in loudness over the length of a program) was considered in ITU-R BS.1770. Loudness of 3-second windows are measured and then the top 5 % and bottom 10 % of these measurements are ignored.
Test Items for verifying the meter were discussed. Some exist already, but need formalising. If anyone wants to contribute to the above, please send an email to the SC-02-01 reflector. Mason will post official documents about the above the items to the SC-02-01 as soon as they are available from ITU.
Recommendation 1864, concerns loudness in the international exchange of television programs.
A Loudness value of -24 +/-2 LKFS is the current value, but there was a proposal that this number should be changed in light of the threshold measurement technique being adopted, which would change the perceived loudness. The value was not changed.
A revision of PEAQ to include multi-channel sound is ongoing.
AES-X187A and AES-X187B, Major rewrite of AES 17
Harris reported that T. Kite is still unwell, but is getting better now and he understands that Kite is expecting to be able to carry on leading the revision work in January 2011. Hopefully, Kite will be able to clean up and progress the documents in advance of the next AES convention, and also attend the next meeting in person.
We discussed companies that may also wish to contribute to the revision work.
Harris will check with Kite about the status of the current document. Ian thinks that the current status may be quite good already.
Harris will check whether an alternative person from Audio Precision can help if Kite is unable to restart work in January 2011.
Liaisons
There was some discussion within the EBU to discuss AV Synchronisation and the possibility of publishing a lip-sync cookbook, but nothing has materialised to date. Mason will propose again to EBU.
SMPTE has a requirements document about AV sync. A demonstration happened in June 2010 in Montreal. P. Treleaven reported that the results were good. Treleaven has posted a report on the SC-02-01 document site. A real test is expected at a TV station at the moment. Please see the document lip-sync-to-AES.doc for more information. Please send any comments to the SC-02-01 email reflector.
New Projects
No new projects were proposed
New Business
There was no new business
The next meeting will be scheduled in conjunction with the AES 130th convention in London, 21 to 24 May 2011.
