Report of the Meeting of the SC-04-04 Working Group on microphone measurement and characterization of the SC-04 Subcommittee on Acoustics held in London, 2011-05-15
The meeting was convened by chair D. Josephson.
The agenda and the report of the previous meeting, held in San Francisco 2010-11-06, were approved.
NOTE Unless stated otherwise, the status of open review projects is, "No action requested or required".
Open Projects
AES42-R: Review of AES42-2010: AES Standard for Acoustics - Digital interface for microphones
Following the publication of the latest revision of this standard, the working group reviewed progress in adoption of AES42 by manufacturers of microphones and other equipment using this interface. A paper noting the use of the standard was presented at this convention. The working-group chair will summarize the products and manufacturers using the standard as a report.
Development Projects
AES-X085 Detailed Professional Microphone Specifications
The chair gave a report on the progress of AES-X085. There was continued discussion about the choice of measurement method for signal and noise level measurements, refer to the 2009-05 meeting report. The consensus now seems to be to use open circuit measurements as required by IEC 60268-4, with "open circuit" for phantom-powered microphones understood to include the phantom powering resistors as part of the microphone circuit rather than as an external load. J. Woodgate suggested that use of a correction for microphone preamplifiers presenting a lower than open-circuit load not be suppressed but permitted if such corrections were necessary to derive results equivalent to open-circuit measurements. The consensus was that correction should be required when the difference between measured and open-circuit values exceeded 0.1 dB.
In the case of noise measurements, while some users of the standard have proposed estimating the noise of the measurement system and somehow subtracting this from the measurement results in order to remove the influence of the measurement, M. Schneider pointed out that this was not necessary, a suitable professional microphone preamplifier being able to provide the necessary gain for the measurement without contributing significantly to the noise of the microphone under test. Once again the consensus was that correction be permitted when the difference between corrected and uncorrected values is more than 0.1 dB, but that actual open-circuit measurements are to be preferred. When corrections are needed due to the limitations of the measuring equipment, they should be stated in the measurement results.
J. Breitlow and the chair discussed progress in the initiation of a new revision cycle for IEC 60268-4. The IEC maintenance team (MT) is being convened and much of the work intended for AES-X085 may be incorporated in the revision of the underlying IEC standard. Specific guidance for detailed specifications needed by users of professional microphones will remain within the AES-X085 project. As the membership of SC-04-04 and the former and proposed 60268-4 MT overlap, this group of people are continuing to work on appropriate allocation of efforts between these two projects.
SC-04-04 members are reminded that there is still a call for participation in MT 60268-4 through the IEC National Committees (NC). If anyone would like to join this effort, contact should be made with the member's NC in order to be nominated as a member of the MT.
AES-X189 Connector for surround microphones
This project has now been transferred to SC-05-02 and the chair has revised the report on this project to incorporate the referenced documents in the body of the report and, at M. Kleiner's suggestion, to clarify that this applied to microphones using an analog interface. The revised report is on the working-group document site.
New projects
No new projects were proposed.
New business
Woodgate suggested that AESSC initiate a new D-liaison with IEC SC48B, specifically covering connectors used in audio such as the XLR, tiny-XLR and surround microphone types. The working-group chair will propose such a liaison by report to AESSC.
The next face-to-face meeting will be scheduled in conjunction with the 131st Convention of the AES in New York, 20 to 23 October 2011.
