MOTM

> Or you can just use the trick Tony Clark showed me.  Just take
> a triangle wave and run it through a full wave rectifier.  Presto!
> 2x Fx.  He has some very interesting VCOs.  Larry Hendry and anyone
> else who attended AHMW2000 can attest to that.

Take it one step further and build a "periodic" full wave rectifier.
(The Interpolating Scanner can do this.)
Now you can get various frequency ratios by changing the input level:

f_out = N * f_in  ,  N = function of input drive.

For certain input levels, a triangle input will result in a triangle
output, only at N times the frequency. Intermediate input levels
will result in a sound similar to oscillator sync (but it works
with *one* oscillator, of course).

And no built-in lag effect as with PLLs.

If you want a similar thing with pulse waves rather than triangle
waves, I have a very simple little circuit built from a few
quad comparators:
http://home.debitel.net/user/jhaible/jh_720_vco_scanner.gif

The word "scanner" is misleading here, because nothing is
actually scanned. The name is derived from the other
Scanner, which can do this frequency multiplication
as a "side effect". (http://www.synthfool.com/diy/jh_ipscan.html)

My suggestion is try the simple comparator based one
to do some first experiments, but let's have the second
one as a regular MOTM module some time to cover
the whole scope of its applications in one module.

JH.