[sdiy] 3 Pole state-variable filters

[Magnus Danielson]

From: "jhaible" <jhaible at debitel.net>
Subject: Re: [sdiy] 3 Pole state-variable filters
Date: Mon, 11 Feb 2002 02:53:14 +0100

> >
> > Sure!
> >
> >       s^2 + s
> > -----------------
> > s^3 + s^2 + s + 1
> 
> Ah, I see. This has 6dB/Oct slopes at both sides (like a 2pole BPF), so
> the 3rd pole must make a difference in the pass band only.

In the style of Matrix-12/Xpander: BP2+AP, LBP and HBP

That is, you can either balance a zero with a pole and avoid slopes,
or you use it on either side of the passband to create a 12dB/Oct-6
dB/Oct division between sides. In the allpass case you have 6dB/Oct
slopes on both sides.

(was to tired to tell you this in my last email)

> 3 poles means one of them must be a real pole.

Indeed.

> I must check this more closely.
> How would it look like in a passive LC implementation ?

You can do this in LC or rather, LCR. It would be fairly simple
setups.

Cheers,
Magnus