Report of the SC-04-04 Working Group on Microphone Measurement and Characterization of the SC-04 Subcommittee on Acoustics meeting, held in conjunction with the AES 114th Convention in Amsterdam, 2003-03-24.

The meeting was convened by chair D. Josephson.

The agenda and minutes of the previous meeting were approved as written.

Open projects

AES42-R, Review of AES42-2001: AES Standards for Acoustics -- Digital interface for microphones
The meeting of task group SC-04-04-D which had occurred earlier in the convention was discussed. Task group chair C. Langen presented its report which has been distributed on the SC-04-04-D reflector as well. Several editorial changes to the standard were noted. Some refinements to the normative part of the standard were also discussed, principally on the topic of allocating bits in the command stream for control and reporting of gain and limiter/compressor settings.

The task group reported that there had been contact from at least one person concerned with patent issues potentially impacting users of AES42. The SC-04-04-D task group reports that since the patent number is sufficient for anyone to obtain information on any patent, it suggested that the notification of potentially applicable patents be revised to include only the patent number rather than try to revise this editorial content each time the assignee of a patent changes. The working group meeting recommended that this approach be implemented in future documents.

There was some discussion about offering AES42 to the IEC, with maintenance of the standard to remain at AES. J. Brown reminded the working group that there was still some controversy about the recommended connector with the "XLD" type, as described in the appendix to the standard, not yet being available. In discussions, SC-05-02 has established that no manufacturer wants to make such a connector with removable keying options, but that there was support for a similar connector that would be available in versions with different keying to accomplish the same goal. He reported that there was a continuing effort in SC-02-02 to determine the desires of the user community in this regard. It was pointed out that the connector issue was separate from the release of AES42 to IEC. The meeting recommended that AES42 be considered for submission to IEC TC100.

Development projects

AES-X62: Psychoacoustics of Microphone Characteristics and AES-X63: Time-Domain Response of Microphones
There was a brief discussion on the status of these projects; the relevant task groups have not met and their chair was not present. Members of SC-04-04 have learned a lot from the discussions on these projects over the years, and particularly from the substantive input presented by J. Green about the work done at her company. Other microphone makers represented in the working group, however, have been unwilling to share their work on this topic and it may be appropriate to discontinue these two projects unless anyone in addition to Green is willing to work on them. Discussion on the reflector is encouraged, with the project to be reviewed at the next meeting to determine whether they should be continued.

AES-X85: Detailed Professional Microphone Specifications
Discussion on this project focused on achieving interoperability with loudspeaker modeling programs, intended to be able to predict complete sound system performance including microphone directionality and room acoustics. Brown suggested that a data matrix be defined to produce a uniform method of characterizing microphone response within this framework. The chair proposed that a task group be established and a new project initiated to define this matrix. [note: During the meeting there was a volunteer to lead this effort but subsequently the chair has been informed that this offer has been withdrawn due to other time commitments]. Discussion on the reflector will be initiated; a volunteer is sought to lead this project.

AES-X93: Recommendations for Revisions of IEC 61938 Clause 7
There was no discussion on this project.

Liaisons

See above regarding AES42 and IEC TC100.

New Projects

No new projects were received or proposed.

New Business

Brown opened discussion about electromagnetic compatibility (EMC) of microphones, specifically susceptibility to broadcast and communications RF energy. He referred to a paper that was presented at this convention by himself and the chair which describes some common problems in condenser microphones, and a simple method of testing for these problems.

In the past, some members have suggested that microphones were considered to be passive devices and thus exempt from EC requirements on EMC. It was generally acknowledged at this meeting that this was not the case, but that there was no unambiguous specification about which directives applied to which microphones. The requirements differ depending on whether the general directive, or those for specific professional markets, apply; there appear to be no directives that apply specifically to microphones.

The next meeting will be held in conjunction with the 115th AES convention in New York, 2003-10.