SC-04-04 meeting, San Francisco, 2008-10

Report of the SC-04-04 Working Group on Microphone Measurement and Characterization of the SC-04 Subcommittee on Acoustics meeting, in San Francisco on 2008-10-03

The meeting was convened by chair D. Josephson.

The agenda and the report of the previous meeting, held in Amsterdam 2008-05-18, were approved as written.

Open projects

AES42-R Review of AES42-2006 Digital Interface for Microphones
C. Langen, leader of SC-04-04-D, reported on their meeting the previous day in which further progress was made toward a sooner-than-required revision of AES42.

There was some concern about a new technical issue related to the reset of AES42-compliant microphones and work is planned between now and the next meeting to resolve this issue with the next revision.

Development projects

AES-X085 Detailed Professional Microphone Specifications
Josephson described progress with the round-robin testing of the noise source now taking place as part of the refinement of measurement techniques within AES-X085. It is anticipated that a spreadsheet for the noise measurements will be compiled and discussed on the reflector before the next meeting. One of the remaining issues in AES-X085 is the graphical presentation of detailed measurement data, and the chair requested that interested parties should present a suggested graphic format at the next meeting.

J. Woodgate reported that the suggested language that had been sent by SC-04-04 to IEC for the revision of IEC 60268-4 had been incorporated into the maintenance of that standard and that the new version would be available for comment in the next few days. The language regarding noise measurements is proposed to require quasi-peak psophometrically weighted measurements, and to strongly recommend that A-weighted slow RMS measurements and one-third-octave unweighted RMS measurements with spectral plot also be included.

Josephson volunteered to participate on AESSC's behalf in the IEC maintenance team for 60268-4.

AES-X093 Recommendations for Revisions of IEC 61938 Clause 7
Progress on AES-X093 was discussed, with Woodgate reminding those present that the IEC had already delayed maintenance of IEC 61938 part 7 in order to accommodate AES input, and urged the WG to proceed with its recommendation. A brief discussion ensued, recalling the many lengthy discussions that had gone before on this topic, and consensus was reached on several key points.

SC-04-04 recommends that IEC 61938 clause 7 be revised to require that devices supplying phantom power to microphones be marked with the phantom power variant (P12, P24 or P48), as is presently required, and that in addition the total current available from all powered inputs of the device together be stated in the manufacturer's literature and on the panel near the relevant input connectors. The device shall be capable of supplying up to the stated current without degradation of performance. In addition, informative language should be included recommending that devices using P48 powering consume not more than 7 mA, noting that this is the value which results in the greatest power being delivered to the powered device.

Josephson and the AESSC secretariat will work together to put this recommendation in the appropriate format for submission to IEC.

Liaisons

There was no new liaison issues.

New projects

No new projects were proposed.

New business

There was no new business.

The next meeting will be scheduled in conjunction with the 126th AES convention in Munich, Germany, 2009-05.

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AES - Audio Engineering Society