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From: minsky@media-lab.MEDIA.MIT.EDU (Marvin Minsky)
Newsgroups: comp.ai.neural-nets
Subject: Re: Discrete Frequency Paradox
Keywords: speech, bilogy, help
Message-ID: <5522@media-lab.MEDIA.MIT.EDU>
Date: 18 Mar 91 15:39:56 GMT
References: <1991Mar12.160801.23281@afit.af.mil> <1991Mar14.174551.7759@ymt.com>
Reply-To: minsky@media-lab.media.mit.edu (Marvin Minsky)
Organization: MIT Media Lab, Cambridge MA
Lines: 14

In article <1991Mar14.174551.7759@ymt.com> mike@ushicom (Puddleglum Marshwiggle) writes:
>What you've described in refered to as Shepard's Tones, named after
>AT&T Bell Labs psychologist Roger Shepard.  The acoustical allusion
>he discovered exhibits the proprerty of circular pitch, that is,
>it sounds like the pitch is constantly rising, but it never goes
>anywhere.

You can produce this effect on a piano, by playing a chromatic scale in
four parallel octaves.  Simply decrease the amplitude of the top not
as it ascends the top octave, and increase the amplitude of the bottom
note in the same way.  The effect works because the combination of
tones of the same pitch class over several octaves produces an
unambiguous sense of pitch class but with ambiguous octave
localization.  Takes just a little practice.