[sdiy] New filter project 8 pole / dual 4 pole morphing filter

[Jaroslaw Ziembicki]

----- Original Message -----
From: "Theo" <t.hogers at home.nl>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Sunday, October 19, 2003 4:04 PM
Subject: [sdiy] New filter project 8 pole / dual 4 pole morphing filter


> This is a multifunction VCF idea I've been sitting on for quite a while.
> The analogue part is already on a PCB and the digital part will follow
soon
> after.
> However some help on the math side, especially the filter transfer
functions
> would be greatly appreciated.


Theo,
Some months ago I built a multimode VCF, and I wrote a C program which
plots the filter's frequency response on the screen.
The filter consists of N current-controlled integrators (CA3080+capacitor+
+voltage follower). All their outputs are being mixed. One mix is the output
and another one is the feedback.
In my program I can change the mix coefficients (from -1.0 to +1.0) and
observe the influence on the frequency response. The response formula
is also written on the screen (as a function of S).
I can send you the C source code if you want.
By the way: I built my filter (with 4 integrators), heard the results and
was
disappointed... I expected much more. I think you'll get better results with
your 8 stages.

Regards
Jarek