|MadSci Network: Biophysics|
This is probably more a question about psychobiology than biophysics, but I'll give it a try. I actually did some experiments using modulation of pure tones and their annoying qualities on myself, so this is purely anecdotal. First, I checked the frequency spectrum of a recording of "nails on blackboard" (NOB)and didn't find it to be different from most normal sounds. What I did find is that high frequency sounds by themselves, although somewhat annoying, don't even approach the annoying quality of nails on a blackboard. Then I played around with a stereo rendition of high frequency pure tones. I found that, when I modulated an 8,000 Hz pure tone in one channel relative to another (so one sine wave changed by 5-20 Hz every second or so), thus producing an audio "diffraction pattern," it got much more annoying. I think that the cyclic augmentation and then cancellation of the tones was much more irritating. It's probably similar to the effect of any "reverbrating" stimulus that we encounter--perceived quality is low or negative. Jim Clack Associate Professor of Biology Indiana Univ -- Purdue Univ
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