MOTM

A Shepard Function Generator is like two quadrature oscillators interleaved
45 degrees out of phase (for an 8-stage, the minimum for a decent effect I
think).

Sine waves would be best, with triangle a second for the purest barberpole
effect.

I have heard the effect demonstrated and it can be quite unusual. Very
interesting sonic illusions can be generated. Also some really wild phase
shifting effcts that never cycle back (the basis of the 'barberpole
phaser').

John S. "Paia" Simonton wrote an article for the February 1983 'Polyphony
Magazine' (later 'Electronic Musician') showing how to do this cheaply. It
was the basis for the Paia EK-9 experimenter's kit. I have always meant to
build it but haven't yet.

For VCAs they had some kind of really cheap 'Hex VCA' board as well at the
time.


-----Original Message-----
From: doctorq@...
To: motm@egroups.com
Sent: 11/17/2000 7:30 PM
Subject: [motm] more module ideas

You know what this crowd needs? A Shepard generator (aka quadrature 
oscilator). It's four LFOs that are 90 degrees out of phase with each 
other (0, 90, 180, 270). When driving four VCOs, the effect is said to 
be an acoustic illusion analogous to the "barber pole" optical 
illusion. I've never heard one but I see the evil "D" brand includes 
one with their MIDI-CV converter, an odd choice, I thought. I also have 
an old Paia experimenter's kit but I can't find the chips or the docs. 
Come to think of it, this sounds kind of like the LFO section of a 
'410.

That's it, any takers? (Stooges, start your engines ;)

Chuck