Report of the SC-04-04 Working Group on Microphone Measurement and Characterization of the SC-04 Subcommittee on Acoustics meeting, held in Amsterdam, Netherlands, 2008-05-18
The meeting was convened by chair D. Josephson.
The agenda and the report of the previous meeting, held in New York, 2007-10-06, 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 the meeting of that task group on 2008-05-17.
Progress is being made on a new draft revision which will be available for discussion and comment before the 2008-10 meeting. Work is being done on a high speed Digital Phantom Power (DPP) interface that will permit a firmware upload to be performed on a microphone in less than the hours required to do it over the regular serial DPP.
Development projects
AES-X085 Detailed Professional Microphone Specifications
Discussion concentrated on the round-robin tests by which microphone manufacturers are validating their measurement performance. At present, a calibrated noise source made by DPA is being circulated around the participating labs to explore the fairly large spread in noise-level values noted among the various labs' measurements of actual microphones.
M. Schneider presented an in-depth analysis of the earlier microphone tests with some statistical processing. Generally, labs are able to measure sensitivity to within less than +/- 2 dB of each other, while noise level is reported with a potential error of up to almost 6 dB. This discussion will be continued in San Francisco at the 2008-10 meeting.
AES-X093 Recommendations for Revisions of IEC 61938 Clause 7
Discussion had been going on via the email reflector regarding phantom power of microphones. J. Woodgate reminded the meeting that this was an interface standard and should really involve people from both sides of the interface, not only the microphone side. It was decided to send an invitation to console makers and other affected parties to join in this process.
Further discussion on the history of phantom power and the limitations of the current draft continued. It was generally felt that the present approach of trying to address behavior of the whole multi-channel powering device was better discarded in favor of discussing the behavior of each individual "outlet" for phantom power.
H. Jahne suggested that the standard specifically provide for alternate methods of phantom powering that sensed whether phantom current was being drawn and if not, to shut off the phantom voltage. J. Wuttke presented "Some Remarks on Phantom Powering" which was originally presented in 2006, giving some details of the evolution of phantom power.
Discussion will continue on the reflector with a goal of further participation from affected parties to be discussed at the 2008-10 meeting.
AES-X160, Powering and analog interface for constant-current line drive (CCLD) transducers
Josephson suggested that, in view of the lack of interest, project AES-X160 should be retired. There was no opposition from the meeting.
New projects
No new projects were proposed
New business
There was no new business
The next meeting wil be scheduled to be held in conjunction with the 124th AES convention in Amsterdam, Netherlands, 2008-05.
