Audio Engineering Society Standards Committee

May 2001 meeting of SC-02-01

[Last printing 17 September 2001] Report of the SC-02-01 Working Group on Digital Audio Measurement Techniques 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 R. Cabot convened the meeting. The agenda and the report from the previous meeting were approved as written.

Current development projects

AES-6id-R Review of AES-6id-2000 AES information document for digital audio -- Personal computer audio quality measurements

C. Travis noted that D. Queen plans to work on a clause or clauses addressing acoustics aspects of personal computer audio. His plan is to have a draft by the time of the next meeting (September 2001). This work is common with SC-04-01. Cabot observed that very few members of SC-02-01 have been willing to contribute to this initiative. Previous e-mail to the chair indicated that J. Woodgate had offered to help.

Cabot noted that a desire to improve existing parts of AES-6id had been expressed by some people at the previous meeting. Cabot asked if there was any new input relating to existing parts of AES-6id. None was forthcoming.

AES17-R Review of AES17-1998 AES standard method for digital audio equipment -- Measurement of digital audio equipment

Travis reported that he had assembled a 35-page digest of SC-02-01 e-mail from 2000-06 on the subject of noise measurement. Aspects include CCIR 468, root-mean-square versus quasi-peak, the merits and problems of A-weighting, and so on. The document has been posted on the SC-02-01 FTP site as AES17-R-NOISE01-001011.TXT.

J. Dunn opened a discussion on the noise modulation test specified in AES17. He explained that this test takes a long time to run. Measurements must be made at multiple signal levels. A multiple fast-Fourier transform (FFT)-based approach could speed up the test. Nevertheless the existing IEC specification for third-octave filters leaves a lot of leeway for different frequency-domain implementations. Dunn stated it would be better if that specification were expressed as a target plus a tolerance, rather than as only an acceptability mask.

Another aspect is that modern converters, unlike many successive-approximation components, tend to show very little noise modulation.

The possibility of adding a swept-d.c. noise modulation measurement to AES17 was resurrected. S. Harris gave a historical perspective. Travis drew attention to some work done at Wolfson Microelectronics which was presented at the AES Silicon for Audio UK conference in 2001-04. This work illustrates the value of swept-d.c. tests with modern digital-to-analog converters. One problem is that many analog-to-digital implementations are d.c.-blocking. Cabot suggested trying a full scale 10-Hz tone, coupled with appropriate time-windowing of the output. Travis suggested acceptance that swept-d.c. tests will not give useful results with all equipment.

AES-X88 Objective Evaluation of Perceived Audio Quality, PEAQ

M. Keyl reported that there has been progress in related forums. For example, the ITU-R PEAQ standard is being revised and will be supported with a validation CD. Also the perceived speech quality (PESQ) standard was approved in 2001-02. These activities have consumed the available resources, so the target date for the draft AES standards project report must be pushed back to 2001-09.

T. Sporer reported that the ITU-R work on formalizing a method for the subjective assessment of intermediate-quality audio, the multi-stimulus test with hidden reference and anchor (MUSHRA) has been completed. An ITU-R liaison statement on this work has been sent to SC-04-07-A.

AES-X102 Liaison With IEC MT61606

M. Furukawa reiterated that the current IEC draft is split into a general part, a consumer part, and a professional studio-use part. Drafts exist for the first two parts. The third part could be based on AES17. Furukawa invited interested parties to attend the IEC 61606 meeting at 08:30 on the following Sunday. Travis underlined that the AES appears to be missing its opportunity to actively contribute to the IEC initiative.

Responding to a question from Dunn, Furukawa confirmed that it should be possible to issue parts 1 and 2 before part 3.

AES-X118 ITU study group 6 liaison

Within ITU-R WP6P a special rapporteur group SRG-3 has been created to work on audio metering characteristics suitable for use in digital sound production. An SRG-3 status report from 2001-03 was distributed.

Cabot asked for input from those present. Dunn reported that he had attended an ITU-R WP6P meeting with the aim of improving liaison. He also stated that progress on the audio metering issue within the AESSC is needed. The value and availability of the ITU-R chosen meter test material was discussed. Travis mentioned a recent AES journal article on metering by B. Katz, and an AES convention paper on metering by J. Emmett.

New projects

No project requests were received or introduced.

New Business

Travis stated he will step down as vice-chair of the group as soon as a new vice-chair is found.

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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