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From: jtn@potomac.ads.com (John T. Nelson)
Newsgroups: comp.sys.amiga,comp.sys.mac,comp.sys.atari.st,rec.music.makers,rec.music.synth
Subject: Re: Sonic Holography.
Message-ID: <2666@potomac.ads.com>
Date: Fri, 4-Dec-87 23:11:29 EST
Article-I.D.: potomac.2666
Posted: Fri Dec  4 23:11:29 1987
Date-Received: Wed, 9-Dec-87 23:31:14 EST
References: <7536@eddie.MIT.EDU> <2476@gryphon.CTS.COM>
Organization: Advanced Decision Systems, Arlington VA
Lines: 43
Summary: Ball bouncing up in ptich...
Xref: mnetor comp.sys.amiga:11975 comp.sys.mac:10674 comp.sys.atari.st:6633 rec.music.makers:1168 rec.music.synth:2095

> Plus, there is an audio illusion I've been looking for, for quite
> a while now. Basically it is an ever increasing tone. 
> 
> There was a display at the Ontario Science center, ohh, 12 years or so
> ago, about MC Escher, that had a ball bouncing "up" an ever increasing
> staircase, with this tone, going up in pitch.
> 
> It went up in pitch for the 1/2 hour I stood there. :-)
> 
> Any clues ?

Yup.  I saw a film of this back in the 70's.  The film was created at
Bell Labs.  The effect is easy to reproduce.  The bouncing sound
is the sum of several frequencies from 0 - 20 Khz weighted by a
gaussian distribution with the hump of the curve starting at the
lowest frequencies.  Now increase the volumn on adjacent frequencies
by sliding the distribution up the scale.  Your ear assumes that the
loudest frequency is the one that you heard the last time but
increased in pitched.  In fact it heard all frequnecies but focused on
the most predominant (loudest).

As you slide the volumn weights towards the high frequencies the
gaussian distribution wraps around to the low end of the frequency
spectrum and the tone that your ear thought it was hearing (the high
end), fades off into the distance.  By this time though it has picked
up the increasing volumn of the lower tones and is following them up
the scale.

Repeat endlessley.

All this time we were watching a film of a ball bouncing up and
Escheresque staircase and feeling like a bunch of laboratory mice.



-- 


John T. Nelson			UUCP: sun!sundc!potomac!jtn
Advanced Decision Systems	Internet:  jtn@potomac.ads.com
1500 Wilson Blvd #512; Arlington, VA 22209-2401		(703) 243-1611

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