AW: VC delay module ideas?

[Ian Fritz]

Juergen --

This is very exciting. I think it would be great to develop analog PM
technology. Please keep us posted on your progress.

I've been thinking about this problem also, but along somewhat different
lines. To me, Karplus-Strong and the Stanford delay-line implementation
of PM are convenient but rather unphysical representations of the real
world.  So I hope to avoid: a crude analog implementation of ... a crude
digital implementation ... of an analog (physical) model. I'd rather try
to make a direct, if crude, analog implementation of the physics without
the delay-line approach. In other words, an analog computer for the
one-dimensional nonlinear differential equation. So far I haven't made
much progress. My approach would be to simply use a sawtooth VCO to
provide the necessary delay and timing information. The VCO would then
in some sense be a pilot or guide to the nonlinear relaxation
oscillator. I think I can see how to implement the necessary nonlinear
functions. (Your interpolating scanner would be the ultimate method,of
course.) Where I'm stuck is with how to implement or approximate the
convolution integral that appears in the theory. The delay-line approach
sidesteps this issue by doing a kind of folding as it goes along, but
it's not exactly the same thing. 

A good reference for the physical models is this review: "On the
oscillations of musical instruments", McIntyre, Schumaker, Woodhouse, J.
Acoust. Soc. Am. v. 74,p. 1325, 1983.

  Ian



Haible Juergen wrote:
> 
> The main reason why I want to build a tracking (i.e.
> V/Octave) delay is the use as sound source (Karplus /
> Strong - sp? - and "poor man's physical modelling" stuff.).
> The main reason why I have not yet built a tracking delay
> is the analogue filter problem. Any analogue filter included
> in the feedback loop would detune the whole thing.
> Ok, put the anti-aliasing filters out of the loop, but you
> still *want* to control the frequency response of the feedback.
> So here you have one case where digital filters are
> superior !
>