Nonlinear circuit ideas needed

[jorgen.bergfors at idg.se]

Wouldn't Juergen Haible's Interpolating scanner fit the bill? Or at least be 
something to start with? http://www.synthfool.com/diy/hj.html

/Jorgen





MIME:ijfritz at earthlink.net on 98-08-06 06.49.56
To:  synth-diy at mailhost.bpa.nl @ SMTP 
cc:  (bcc: Jorgen Bergfors/IDGSE)
Subject: Nonlinear circuit ideas needed 

Hi all --

I've been thinking in a somewhat vague way of trying to build an unusual
kind of analog sound source. It might be refered to as a
pseudo-physical-modeling synthesizer. It would be a nonlinear relaxation
oscillator operating in a manner similar to one-dimensional theoretical
behavior of musical instruments, but without the delay-line type
implementation used by the Yamaha-Stanford axis. My idea is to generate
the needed delay from a standard VCO, which would run in parallel with
and "guide" the relaxation circuit.

To start with I need a certain kind of nonlinear circuit, and I wonder
if any kind listers could point me in the right direction to find what I
need. The required circuit needs to have a transfer function with an
inverted "U" shape. To understand why this is needed think of a clarinet
mouthpiece. With a small blowing pressure the air velocity into the
mouthpiece increases monotonically with pressure, but beyond some point
the pressure closes the reed off to where the flow decreases with
increasing pressure. Eventually the velocity becomes zero at all
pressures beyond a cutoff point. The negative (mechanical) impedance
region is what makes the clarinet operate as a relaxation oscillator.
The circuit needed to simulate this behavior should have a way to adjust
the shape of the response curve (preferably under voltage control!) to
obtain different timbres and response characteristics. 

Any ideas? Anybody else interested in working on this? A good reference
for understanding physical modeling is "On the oscillations of musical
instruments", ME McIntyre, RT Schumaker and J Woodhouse, J. Acoust. Soc.
Am., v. 74, p. 1325 (1983), for anybody interested in digging into the
physics.

  Ian