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 London, UK., 2011-05-15
The meeting was convened by chair S. Harris.
The agenda was approved. The report of the previous meeting, held in San Francisco, 2010-11-06, as amended on 2010-11-16 was approved.
Open Projects
AES-6id-R Review of AES-6id-2006: AES information document for digital audio - Personal computer audio quality measurements
scope: to specify measurements of audio quality in a personal computer (PC) environment.
status: Please review for action in 2011
intent: Review initiated: 2006 intent target: 2011
goal: Status report; goal target: 2011-05
This information document is now due for it's 5-year review. Proposed to re-affirm.
AES-12id-R; Review of AES-12id-2006: AES information document for digital audio measurements - Jitter performance specifications
scope: This information document reviews various ways of characterizing and quantifying jitter, and refines several of them for audio purposes. It also attempts to present a common, unambiguous terminology. Its focus includes wideband jitter, baseband jitter, jitter spectra, period jitter, long-term jitter and jitter signatures. Comments are made on jitter transfer through phase-locked loops and on the jitter susceptibility of audio converters.
status: Please review for action in 2011; reaffirmation presumed
intent: Review initiated: 2006 intent target: 2011
goal: Status report; goal target: 2011-05
This information document is now due for it's 5-year review. Proposed to re-affirm.
Development Projects
AES-X102 Liaison with IEC TC100 PT 61606, Audio and audiovisual equipment - Digital audio parts - Basic measurement methods of audio characteristics
scope: to harmonize digital audio measurement standards through a working relationship between SC-02-01 and IEC TC 100 MT61606 in conjunction with the category-D liaison between AESSC and IEC TC 100.
status: No action requested or required
intent: Review initiated: 1998 intent target: Continuing
goal: Status report; goal target: Continuing
T. Kite commented that IEC 61606 looked in good shape, and that the new revision of AES17 will refer to IEC 61606.
AES-X118 Liaison with ITU-R study group 6C SC-02-01
scope: Liaison with ITU-R Working Party 6C, Measurement aspects status: Noted recent agrement on gated loudness measurements for revision of BS.1770
intent: Liaison initiated: 2001-03 intent target: Continuing
goal: Status report; goal target: Continuing
Recent ITU-R communications include a discussion of short-term loudness metering and low-frequency (LFE) levels. The meeting also heard that ITU-R BS.1770 was revised recently to include a gating function. A proposal to standardise the oversampling filter coefficients in the true-peak metering section of BS.1770 has just been made to ITU-R WP6C.
AES-X187A Revision of AES17 AES standard method for digital audio equipment - Measurement of digital audio equipment, AND
AES-X187B Companion ID to AES-X187A, AES standard method for digital audio equipment - Measurement of digital audio equipment
Kite has been working on the above pair of draft documents, drawing from material on the document site, I. Dennis' emails, and in particular IEC 61606-3.
He has worked through about half the necessary edits, but there were several topics that needed discussion, as follows:
- Window Width filters. Applied to FFT processing and commonly in use in test equipment. The noise floor of the system looks like it is varying according to the number of samples in the FFT acquisition. The proposal is that the bin width be adjusted according to bandwidth in Hz, which therefore varies the bin width acros the spectrum. Tom will send a proposal about how to set the bin width in a specific way so that all equipment can use the same approach;
- Recommended units. Add a table to define the units to use for certain measurement types. For example, dBu for Output Level, analog. We discussed cross-domain gain, for example dB (FS/Vrms) for ADC gain. We always need to define full scale.
- Deviations from a standard weighting filter. The possibility of permitting implementors to vary the weighting filter from the standard filter to some other, specified filter, was discussed. We agreed that we should mandate a specific filter for the standard. Any discussion of flexibility should be reserved for the companion information document (AES-X187B). We agreed that there should be a statement at the beginning of the standard that states that if the results of a measurement are according to AES17, then there can be no changes to the conditions defined in AES17. If the conditions are changed, then the results cannot be stated as made according to AES17, and the results should define the conditions used. Kite will include this in the new revision.
The meeting agreed that stating that measurements were made according to AES17 does not mean that all possible AES17 measurements were made.
Kite will send an email to the working group with specific questions on matters yet-to-be-determined for members' comments.
Kite will arrange for a brief announcement and invitation for people to help with updating the standard, including a statement about adding new measurements, for example multi-tone and exponential swept sine measurements, which are particularly valuable for production measurements.
We agreed to have a new measurements email thread, for example "bonger test". Yonge will find a "bonger" test source reference from N. Gilchrist or L. Fielder.
Liaisons
No new liaison matters.
New Projects
Discussion about characterising the software plug ins and tools running on a PC. The conclusions are that no special additions are needed to enable measurements to be made on software based equipment.
New Business
A question has been received concerning A/D Converter testing for archival applications.
An email about this is expected from Chris Lacinak.
There will be a conference call to progress the work to revise AES17 towards the end of June 2011. Kite will send out an invitation in the week of 16 May to confirm details.
The next face-to-face meeting will be schediuled in conjunction with the AES 131st Convention to be held in New York, NY., US., 20 to 23 October 2011.
