Re: [sdiy] 3 Pole state-variable filters

[Magnus Danielson]

From: jhaible at debitel.net
Subject: =?ISO-8859-1?Q?Re: [sdiy]?= 3 Pole state-variable filters
Date: Tue, 12 Feb 2002 11:27:23 +0000 (UTC)

> 
> > > non-minimal-phase BPF filter. Ok, no need to choose the zero
> > > equal to the negative real pole,
> 
> > Nope . You get bp2+ap only if zero is positive .
> 
> Sure. The real pole must be negative (for stability), and the
> zero to make an AP must be "the negative of the pole"
> (same absolute, opposite sign), which means positive.
> I see that "negative" must have been confusing. What is the
> precise Englich word? Complementary?

Yes, but it would be confusing since in this case complementary is
mostly used to mean complemented on the imaginary axis where as you
are out for the complement on the real axis. Technically correct, but
could lead to confusion amongst those that does not interprent the
word in its wider sense.

Actually, you do not NEED to put it on the other side of origo, you
can put the pole and zero at the same value if you want, but they
would also cancel each other in phase. This is however usefull if you
allow for change of the relative position of the pole and zero, which
is BTW commonly done.

Cheers,
Magnus