Audio Engineering Society Standards Committee

May 2002 meeting of SC-04-01

[Last printing 20 May 2002]
Report of the SC-04-01 Working Group on Acoustics and Sound Source Modeling, of the SC-04 Subcommittee on Acoustics meeting, held in conjunction with the AES 112th Convention in Munich, Germany 2002-05-12.

Chair R.Campbell convened the meeting. The agenda and the report from the previous meeting at the AES 110th Convention were approved as written.

Current development projects

AES-X05 Room and Source Simulators: Specification and Evaluation of Computer Models for Design and Auralization; Recommendations for Transportable Input and Output Files

A PTD is on the FTP site as: X05-WG-PTD-010614.pdf . The chair reported that he has put the EASE compatible test room posted by W. Ahnert into CATT but some additional testing remains to be done. The results of this will be posted.

AES-X70 Smoothing Digitally-derived Frequency Response Data on A Fractional Octave Basis

The meeting decided to recommend, via this report, retirement of this project. If no objections are received within two weeks of this posting, the chair will request the retirement.

AES-X83 Loudspeaker Polar Radiation Measurements Suitable for Room Acoustics

The discussion concentrated on two items, the proposal submitted by B. I. Dalenback and another submitted by B. Olsen, direct impulse response, by means of a demonstration at the previous meeting. See the report of the December meeting.

It was the consensus of the meeting that impulse responses should be available as stand-alone WAV files for those modeling programs that are prepared to accept them directly. The Dalenback proposal would have optionally embedded them in the binary distribution.

After considerable discussion, it became apparent that these ideas can be merged whereby the IRs can be made available on the distribution media as WAV files, and pointed to within the binary distribution block. In addition, a pointer to one text header file can be used to furnish the extra non-radiation data needed to complete the WAV file-set information.

This method allows both types of radiation data to be furnished to a modeling program. A loudspeaker manufacturer would have the option of providing the IR?s, or of converting the IRs to text format, including whatever post-processing is needed to fit the desired data density. The resulting text file would be made available to the user, or it can be converted to a DLL -style binary data block and made available in that fashion. Essentially, this adds one additional item at the front end of the flow diagram shown in the Dalenback proposal.

The meeting felt that the following data should be made available:

a) impulse response files together with a descriptive text header;

b) text-only data formatted in a way to allow the construction of radiation balloons;

c) a binary data block containing all of the radiation information which, depending upon the format required by the modeling program, may contain embedded IR's or it may reference IR's stored elsewhere on the distribution media.

It also felt that the document should include:

a) transformation of IRs into text-based radiation data either as IRs or a proprietary data acquisition system;

b) transformation of text data to binary data in preparation of creating the binary data block;

c) Merging of binary radiation data with other data (or pointers to IRs) and final formatting for modeling program direct binary input compatibility.

These items, including an example of a flow chart for the information, are included in proposed task-group draft X83-ptd-rc-020517.pdf on the FTP site.

The meeting recognized that for many applications, IR distribution is not necessary, and the route through text, or text followed by a DLL, will be sufficient to provide meaningful room acoustic modeling data. In addition, some manufacturers may be reluctant to furnish IRs, and may therefore use the alternate route such as the Dalenback proposal. Note that the WAV file data set has been previously discussed and one possible file structure identified, but not yet incorporated into a PTD.

Some examples of current use were pointed out by members:

-- The EASE program can accept manufacturer's IRs directly and produce radiation pattern data for use internally to the program. It can also work with text radiation balloon data.

-- The CATT program can accept text radiation balloon data and also a proprietary DLL-based binary data block created from manufacturer's measured radiation data.

-- Many small loudspeakers typically used for wall-mounting or ceiling mounting can be adequately modeled using rather low-density radiation balloon text data.

-- Musical instrument directivity, a critical issue for accurate auralization, is usually given in sparse text balloon format.

The chair will attempt to merge these ideas into a single draft document and post it by 2002-09-01.

During the discussion, mention was made of a measuring system using a simple file naming convention for IRs. For reference, the URL is

AES-X108 Measurement of the acoustical and electroacoustic characteristics of personal computers.

D. Queen explained that SC-04-01 was assigned this task as a new project because the expertise for it did not reside in SC-02-01 to which the review project, AES-6id-R, is assigned.

He noted that the intent of AES-6id is to guide the computer manufacturer, who may have limited expertise in-house, in making relatively simple sets of measurements to quantify the audio quality of personal computers. The acoustic procedures in the PTD on SC-0401-D FTP site, 6ID-R-A1-PTD-DQ-011117.pdf will represent an improvement over what is done now, even if they are not up to laboratory practice for loudspeakers, microphones, and product noise.

Members suggested that the document emphasize that measurements are to be made on one channel at a time.

Several members noted that, contrary to the draft, manufacturers of test equipment do not provide guidelines for the use of their products, so that the minimum acoustical requirements of the room including dimensions, positions, and background noise must be included.

The group also recommended that test signals be provided on the AESSC Web site to allow real-time analyzer measurements.

The discussion also provided a standard means to position laptops with respect to the test microphone and sound source.

After considerable discussion, the group consensus was that distortion measurements should not be included. Queen noted, however, that these measurements are included in current industry documents, so AES-6id should explain why they are misleading.

Queen will revise the PTD according to the discussion.

Members urged that WG members try measuring their own equipment as an indicator of potential technical problems.

AES-X122 Loudspeaker Radiation and Acoustical Surface Data Measurements: How They Apply to Usage Environments

The chair noted that this project was initiated at the Amsterdam meeting and that conceptually, this work treats special wall surfaces such as diffusers (both active and passive) as secondary sound sources. Thus the same radiation data density as used in primary sources under discussion under project AES-X83 might apply for purposes of room acoustic modeling.

The working group decided to request that the project be suspended until the work on AES-X83 and AES-X05 is further advanced.

New projects

No project requests were received or introduced.

New Business

There was no new business.

The next meeting is scheduled to be held in conjunction with the AES 113th Convention in Los Angeles, CA, US.

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(C) 2002, Audio Engineering Society, Inc.