[sdiy] PSpice to VST anybody?

[Aaron Lanterman]

On Fri, 22 Apr 2005 jhaible at debitel.net wrote:

> Extract the significant poles and zeros from the AC courve
> (there must be algorithms for this - it's standard in Radio Frequency
> analysing software), then model it with your usual s-domain to
> z-domain methods. No time variant stuff required.
> I don't aim for anything as complex as a VCF.
> Just a single, time invariant, linear filter courve.

The final filter you implement will, by its nature, need to be in the
time domain, but you can get the coefficients from your z-domain
representation if you multiply out the pole-zero terms to get a
polynomial. As I tell my students, z-transforms are an analytical tool -
there aren't actually any z-transforms in the computer. ;)

If you're doing an FIR filter, the standard way to do filter design is
with the Parks-McClellan algorithm (I'm very lucky to have Jim McClellan
just down the hall from me - a brilliant, really nice man, and a fantastic
mentor). There's other algorithms for IIR filter matching, can't think of
what they are off the top of my head. MATLAB has it built in if you have
the Signal Processing toolbox (I think) - but I'd be surprised if there
wasn't some code to do Parks-McClellan sitting out there on the web
somewhere already.

- Aaron

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