NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/fractals/532

Internet Message Format | 1993-01-02 | 1.6 KB

Path: sparky!uunet!wupost!usc!randvax!edhall
From: [e-mail] (Ed Hall)
Newsgroups: sci.fractals
Subject: Re: Fractal sound?
Message-ID: <[e-mail]>
Date: 3 Jan 93 04:06:20 GMT
References: <[e-mail]>
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In article <[e-mail]> [e-mail] (Rich Chong) writes:
>I heard that there is a fractal tone that sounds like a tone of
>a forever increasing pitch, but in reality doesn't.
>Is there a name to this? Can someone post a sample or a generator?
>Thanks.

I'm not sure if I'd call it a "fractal," but the so-called "Shepard
tone" is such a sound.  The sound consists of a bank of rising
tones--say, ten tones in total--each an octave apart and rising in
unison.  A given tone starts at a very low frequency and with zero
amplitude, then gradually fades in as it rises, becoming loudest around
the fifth octave and gradually fading out to zero amplitude when it
reaches the tenth octave--and then starts all over again at the lowest
frequency.

Because of the gradual fade-in/fade-out, the starting and ending points
of an individual tone are not heard, and the ear tends to focus on the
tones pitched around the fifth octave, hearing them as a group of
"endlessly" rising tones.

Psychologist Roger Shepard discovered the principle behind these tones,
while Jean-Claude Risset developed the "endless glissando" I've just
described.  I have a CSOUND instrument which produces these tones, if
anyone is interested and has CSOUND.

        -Ed Hall
        [e-mail]