[sdiy] What is a quadrature oscillator good for?

[Don Tillman]

   > From: "jhaible" <jhaible at debitel.net>
   > Cc: <synth-diy at dropmix.xs4all.nl>
   > Date: Mon, 15 Sep 2003 02:35:23 +0200
   > 
   > > Does this ever come up in real life?  Sure, if you want to accurately
   > > model the position of a freely rotating object.  That's one of my
   > > goals (though it might not be anybody else's goal).
   > 
   > I clearly see applications for this: If you want to _stop_ a panning
   > movement, infinite phaser, or simply put a FS into zero shift
   > without a bypass switch.

Yes, indeed!

Also a scratching DJ turntable simulation (NOOOOOOOO!!) or a Leslie
speaker that can be arbitrarily positioned.

I also see a lot of use in chaotic systems.  I mentioned on this list
some years ago about being impressed with the Chaotic Pendulum exhibit
at the Exploratorium in San Francisco.  Here's a nice page about it:

http://www.exploratorium.edu/exhibit_services/ebtp/exhibits/group1/chaotic/index.html

This is a T-shaped pendulum with with three little pendulums hanging
off the ends and it that makes the most wonderfully chaotic patterns.
It's really wild to watch the patterns this thing generates.  I was,
of course, thinking about making an analog version of it.  But it's
just not possible without being able to model rotating objects first.

More philosophically, I think it's worth exploring rotating objects
as a basic electronic music building block.

   > But won't you have problems with leakage here, even with the
   > trapezoid core?

It hasn't been a problem.  For any given quarter cycle, one of the
capacitors is just held at a reference voltage and the other gets to
travel between the two reference voltages.  If the travelling
capacitor is off by a little bit due to leakage, opamp offset, or
whatever, that's just a question of trimming the 0 Hz point.

  -- Don

-- 
Don Tillman
Palo Alto, California
don at till.com
http://www.till.com