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 Los Angeles 2014-10-10
The meeting was convened by chair D. Josephson.
The draft agenda and the meeting report from Berlin, 2014-04-28, were approved as presented.
Development projects
AES-X085 Detailed Professional Microphone Specifications
As the work concerns nearly every member of SC-04-04, the AES-X085 project nominally assigned to SC-04-04-E is being discussed in the main SC-04-04 meeting.
Work continues in AES-X085 on the refinement of microphone self-noise metrics, and methods for assessing sensitivity to wind. E. Brixen and J. Breitlow reported on cooperative tests done by DPA, Schoeps and Neumann over the past few months on reducing the differences between various labs' measurements of wind sensitivity. Some results of the tests were presented, including measurements of the same DPA microphone with and without windscreen, at various angles of wind incidence. Shure also plans to participate in the tests. The group members use a wind generator similar to that shown in IEC 60268-4; some operate at the recommended 10 m/s while others use a wind speed of 5 m/s. It was considered that 5 m/s may be more appropriate in order to reduce acoustic noise from the wind generator.
H. Riekehof has uploaded to the SC-04-04 document site MATLAB code to calculate quasi-peak noise values from a .wav file, along with supporting documentation. This is part of ongoing work in AES-X085 to reduce the differences among labs testing microphones for noise. C. Struck reported having reviewed the code and believes it is compliant with the recommendations of the ITU BS-468.4 metric it is intended to emulate, but complete testing has not been done. There was some concern that nothing would really be known without validation using several known noise test signals, both using proposed algorithms and known legacy test instruments such as the Sennheiser UPM level meter, which at least three members have in their labs.
Riekehof's report includes validation using a noise signal from an AP 2700. S. Temme uploaded a white noise test signal to the SC-04-04-E document site in 2013, but members at the meeting had not seen it there. Several other members suggested that they would prepare test signal files, and the chair suggested that a "noisefest" be held in conjunction with the next meeting. Each file should be at least 48 kHz, 16 bit and include a note as to the value of a 0 dBFS sine wave at 1 kHz, in SPL.
Liaisons:
There were no liaison reports.
New projects
Network control of microphones: Breitlow reported on the initiation of a project (which the chair will submit) on audio network control of microphones, to define control interface parameters and naming conventions for microphone operational controls to be accomplished over a network interface. It is not necessarily linked to AES42. M. Yonge suggested that SC-02-12 be informed of this work to assure compatibility with X210 and AES60.
Breitlow also reminded the group that the 5th revision of IEC 60268-4 has been published and that the revision cycle will begin again soon. Members are encouraged to review this document and suggest any changes that are required.
The next meeting will be held in Warsaw, Poland, 2015-05, in conjunction with the 138th convention of the AES.
