SC-04-04 meeting, October 2003

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 115th Convention In New York, 2003-10-12.

The meeting was convened by chair D. Josephson.

The agenda and the report of the previous meeting were accepted 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 on 2003-10-11 was discussed. Task Group chair C. Langen presented its report which has been distributed on the SC-04-04-D reflector as well. Langen reported that several editorial corrections had been made, and several items discussed which had been left open as of the previous meeting. Some of these items were moved from a �red� status requiring further discussion, to a �blue� status indicating task group consensus. The items reported to be remaining in the �red� status, which will be discussed further at the next meeting of SC-04-04-D, were principally concerned with the definition of parameters to be passed to a compressor/limiter integrated into the digital microphone or similar device.

Development Projects

AES-X62: Psychoacoustics of Microphone Characteristics and AES-X63: Time-Domain Response of Microphones. There was a brief discussion of the status of these projects. No further work has been done, and in accordance with a preliminary decision taken at the March 2003 meeting, one more review will be presented, at the May 2004 meeting, before the Working Group recommends continuing or cancelling these projects.

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

AES-X85: Detailed Professional Microphone Specifications The chair is pleased to report that there was significant progress toward consensus in this effort. In brief, it is recognized by the Working Group that no known microphone manufacturer today publishes specifications fully in accordance with IEC 60268-4, which is the applicable International Standard. Discussions on this project in the past have been based a superset or more detailed specifications than are called for in IEC 60268-4, but at this meeting the emphasis was shifted instead to a subset of the IEC standard, with which a consensus of members could agree. The concept of publishing this as an AES recommendation in the form of an Information Document was discussed. The recommendation would call for a uniform graphic format for an agreed-upon set of parameters to describe a given microphone type.

The parameters are to include at least:

  • Electrical and physical parameters per IEC 60268-4
  • Frequency response on-axis and at 15 degree intervals and the significant null(s) of the pattern, should null(s) not fall on a 15 degree incement, 1/20th octave averaged, including tolerance limits. Substantially identical curves for various angles need not be duplicated. Show on-axis response at 1 m, 0,5 m and 25 mm (using ITU standard artificial mouth at least for the latter).
  • Self-noise of the microphone, 1 octave bands,
  • Show level not to be exceeded.
  • Intermodulation Distortion at 1 Pa and at rated maximum SPL.
Representatives from the 7 microphone manufacturers present agreed to consider producing such a draft specification for one model of their current manufacture for mutual review.

The example article will be a small-diaphragm (<25 mm) condenser microphone having a cardioid characteristic. Manufacturers not making such a model may submit any other of their choosing. All manufacturers are welcome to participate. Templates for the specification graphic layout are to be submitted to the Working Group document site in advance of the May 2004 meeting, Those participating are to bring the specification design and an applicable microphone to the May 2004 meeting, where arrangements will be made to send the package of applicable microphones on a round-robin schedule to each of the participants to qualify their measurement procedures and to identify areas where additional detail is needed. The results of the round-robin tests will be reported to the group and summarized at the October 2004 meeting.

There was also discussion of the format for supplying individual response curves to customers. There remains some friendly rivalry between manufacturers who choose to supply individual response curves with delivered microphones and those who do not. Without commenting further on this aspect, there should be no misunderstanding of the Working Group�s intention, which is not to address the topic of individual response data at all. The entire basis of this project, and any graphic or data exchange format that might come from it, is to represent the manufacturer�s own specification, including tolerance limits, not the report of the performance of any individual unit.

The goal is to produce a uniform frame of reference, compliant with IEC 60268-4, including uniform test conditions, that most microphone manufacturers can accept, so that otherwise similar units from different manufacturers can be compared. The IEC standard permits too much variation in test procedures for comparisons to be directly made. The Working Group hopes to define a uniform subset of the conditions specified in the IEC standard, that leading microphone manufacturers can agree upon in a way that is not possible today.

J. Brown brought up the need in the architectural acoustics and sound system design community for a microphone performance data matrix that would allow sound system modeling to include the directional response of the microphone. There were no volunteers to take on this aspect of additionally detailed microphone performance results.

Liaisons

See above for comments on liaison with SC-04-04-D.

New projects

No new projects were proposed

New Business

There was no new business.

The next meeting was scheduled for the next AES convention in Berlin, 2004-05.

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