> I'll throw out an idea. The only digital synth I own is an Emu
> Ultraproteus
> with its Z-Plane filters. These are 14-pole parametric filters that
> allow them
> to mimic a wide variety of filters (moog, flange, phase, etc.). Now I
> realize
> that controlling such a beast without a computer would be difficult, not
> to mention the cost of something like this.
You're making a good point here.
The possible variations of filters are infinite.
Try and experiment with several filters in parallel, adding or substracting
the outputs, and sweep them with the same CV, or with different CVs.
Phase difference between the two signals will provide a multitude
of unexpected filter courves, and I promise you (the user) can "invent"
new filter types with just a set of a few basic filters.
As for the design, it makes sense to create solid building blocks
that start from existing designs. The Moog ladder being one of them.
And as many pointed out, no Moog ladder is like another Moog
ladder, so it makes sense to explore a region that other Moog-style
circuits on the web don't cover.
> But it seems even a single
> pole parametric with continuous voltage control from cut (notch?) to
> boost (bandpass?) and VC of Q and frequency would be very interesting.
For Q you need at least 2 poles, but I get the idea.
> Several of them cascaded could produce some interesting responses.
You can re-calculate ∗every∗ (linear) filter function into a series of
2-pole state variable filters. You can even do this on paper,
mathematically (but at least I need a textbook beside me to do this (;->)).
So when you buy 3 of the SEM-style VCFs you can theoretically
create ∗any∗ filter response up to 6 poles and 6 zeros. It practice,
you can do this as well, but you'll find that the "useful" (whatever this
is) configurations are there as well as many less useful settings.
Maybe that's why this "z-plane" idea of Emu's is not as popular as
the "classic" filters: too many degrees of freedom.
JH.