AES Section Meeting Reports

Detroit - February 7, 2008

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The February 7th meeting of the Detroit Section was held at Alpine Electronics. David Clark presented "Perceptual Transfer Function (PTF) measurement system, a Progress report." He started off giving an overview of his Listening Technology subjective evaluation technique. This method is widely used within the automotive industry and has been the inspiration for Mr. Clark's advancement with PTF.

After a short business meeting where new officers were elected or re-elected, the presentation begun with some history of automotive audio. Starting with 1930 Motorola car radios and bringing technology up to present day. The first Bose system (1983 Cadillac) was discussed and the more recent B&O Audi A8 was also presented.

The interest in in-car audio is, if anything, growing. And the needs for industrial processes and procedures to ensure consistent high quality output are as relevant as ever. It was this realization that inspired the development Listening Technology in the 1990's. By agreeing on an "Ideal" sound or goal for a system, trained evaluators are able to build conclusions about a system from small comparison tasks. The results are reliable un-biased evaluations as free from opinion and emotion as possible.

The Goal of PTF is to use objective measures to simulate subjective or perceptual response to a sound systems. Starting with Frequency response, or to use perceptual language, tonal balance, high level analysis of a spectrum allows attributes to be extracted and given a score by the computer. This has been extended to loudness tests with a multi-tone test measuring compression and distortion simultaneously.

Mr. Clarks most advanced work with PTF is location detection. Using an advanced ear-brain model sound stage, imaging and ambiance can be measured using inter-aural level differences, inter-aural time differences and inter-aural group delay. This was demonstrated at the meeting. Attendees could see how the different image detection methods work at differing frequency ranges and could see the detection of left, right and phantom images.

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AES - Audio Engineering Society