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Plenary SQS 2008

William M. Hartmann

William M. Hartmann, a professor of physics at Michigan State University is a past president of the Acoustical Society of America of which he has been a Fellow since 1983. Prof. Hartmann received a BS in electrical engineering and physics from Iowa State University in 1961 and earned his PhD in condensed matter physics in 1965 as a Rhodes Scholar at Oxford University. After three years as a research assistant at Argonne National Laboratory, he joined Michigan State. In 1976, Prof.Hartmann's work which had been focused on lattice dynamics and the electronphonon interaction took a sudden change of direction. Inspired by teaching a musical acoustics course, he became interested in human hearing. He now works on sound localization, pitch perception, and signal detection, and has developed methods of sound recording that enable recreation of the listening environment of a live musical performance.

Abstract: Listening with two ears benefits hearing in two ways, through binaural summation and through binaural comparison. Binaural summation means that two ears are better than one independent of any special differences between the signals at the two ears. Binaural summation leads to lower absolute thresholds, increased loudness, and improved discrimination for both intensity and frequency. Binaural comparison is a special capability of the central nervous system that is sensitive to the differences in signals at the two ears. Binaural comparison processes occur in parallel with binaural summation process though the comparison operations lag in time. Most importantly, binaural comparison allows listeners to localize sounds by their azimuths. Recent research on sound localization has emphasized the poor binaural quality of signals normally available in the world, which leads to increased amazement at the sophistication of the central binaural comparator. Binaural comparison leads to improved detection based on the binaural differences themselves. The comparison process also plays an important role in the de-coloration and de-reverberation effects that distinguish ordinary human hearing from sound recording.


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