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Psychoacoustics With Hannes Müsch

Mr. Müsch is affiliated with both the Center for Communication and Digital Signal Processing and also with the Institute for Hearing, Speech, and Language. He is currently a doctoral candidate but already holds master's degrees in electrical engineering from both the Technical University of Dresden and Northeastern. Previously he was a consultant with Muller BBM, an acoustical consulting firm in Munich.

The first portion of the talk was on "Sound Localization:The Miracle of Three-Dimensional Hearing."With so much current interest in sur- round sound and cinema effects, an understanding of the human percep- tion mechanisms for direction, elevation, and distance is important.

The "Duplex Theory" was proposed and investigated by Lord Rayleigh in 1907 and involves both time differences and intensity differences. If, in the horizontal, a sound source is off-center, the closer of one's two ears receives its emanations sooner. The brain can process this interaural time difference (ITD) to tell the listener something about the source's relative azimuth.

But information also comes from the interaural intensity difference (IID). Because of the "shadowing" effect of the head itself, sound from one side is perceived as louder by the ear on that side. This effect, and therefore one's ability to utilize IID information, increases for shorter acoustic wavelengths.

If a listener has two ways to figure out where a sound is coming from, is one of them more important that the other? In principle, each is enough, but ITDs are more efficient with low-frequency sounds while IIDs are better for high frequencies. In synthesizing "left-ness" and

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