Shepard Tones at last

[Jim Johnson]

For what it's worth, this illusion is pretty easy to recreate on an
Xpander. Just use four voices, set to identical values, with the LFOs set
to sawtooth but each out of phase by 45 degrees. Run each sawtooth thru a
tracking generator configured to produce a triangle, and use that to
control amplitude. Pretty cool!

Coincidentally, I spent some time last week trying to do this on a Kurzweil
MA-1 equipped sound card. Almost got it, but the effect was a bit choppy
and the aliasing was a little annoying. 

It seems to me that if this effect were produced with the tones falling
instead of rising, and the tones tuned to a diminished 7th chord, it would
be enough to make a person jump out of a window.

Jim Johnson 
Metaphoric Software
-------------------
Makers of Techno Toys
Software for Electronic Music
http://www.technotoys.com
info at technotoys.com


*********** REPLY SEPARATOR ***********

On 3/13/98, at 1:00 AM, KA4HJH  wrote: 

>>>I now have a sample of the Shepard Tones (only ten months after we
>>last
>>discussed it). Does anybody have a place I can put it? It's rather
>>large...
>
>>
>>Hi Terry- How did you do these and how big are they? Has anyone else
>>come forward with a place for them?
>
>John:
>
>I have a 1.3 MB .wav file which is about a one minute sample taken from a
>cassete tape which was released by CCMRA as a companion to the book *The
>Science of Musical Sound* (out of print). It sounds pretty good (16 bit,
>11K) and illustrates the illusion perfectly. All it needs is a home. I've
>had it for a long time and just never got around to telling anybody (it's
>been a rough year, folks).
>
>----------
>For those whose don't want to bother looking it up, here's my original
>posting from April 7, 1997:
>
>René:
>You're referring to the famous "sonic barberpole" illusion invented by
>psychologist Roger Shepard at Bell Labs. The illusion consists of a
>seemingly endlessly rising or falling set of tones. The trick is done by
>simultaneously sweeping eight (or so) sinewaves tuned exactly one octave
>apart. The human ear has a really hard time figuring out which pure tone
is
>the fundamental, so it "slips" periodically, just like an eye watching a
>barberpole (or looking at an Escher staircase). To conceal the tones'
>appearing and disappearing they fade in at one end of the cycle and fade
>out at the other.
>
>To create the Shepard Tones in the analog domain you need eight VCO's,
>eight VCA's and an LFO with ramp and triangle outputs in octature (eight
>outputs 40 degrees apart). Harold Bode used phasers instead of VCO's to
>create his famous "Barberpole Phaser." PAiA used to have a Shepard
Function
>LFO kit, although I think it's long gone now.
>
>[there may still be a schematic at...]
>http://www.hyperreal.com/machines/categories/midi-cv-sync/Paia/image
>
>I could post a sample if anyone's interested; it's too late for me to do
>tonight. [HA]
>
>
>The Science of Musical Sound--John R. Pierce, Scientific American Library
>"Lab Notes: Shepard Functions"--John S. Simonton, Jr., Polyphony, 2/83
>
>[And that's the way it was...]
>
>
>Terry Bowman, KA4HJH