[sdiy] SVF & phase

[Grant Richter]

Mark's question makes me question my assumptions about filters. Maybe
someone can clarify.

I am under the impression that a filter without phase change would not be a
filter at all?

I mean, the phase change with frequency is what allows the amplitude change
with frequency?

Because the amplitude response is the "real" axis of the S plane and
movement along the "imaginary" (phase) axis is how the shape of the real
axis is determined?

> From: patchell <patchell at silcom.com>
> Date: Tue, 26 Nov 2002 12:08:37 -0800
> To: mark s <n0nspaz at mindspring.com>
> Cc: synth-diy at dropmix.xs4all.nl
> Subject: Re: [sdiy] SVF & phase
> 
> Well, if you could build a filter like that, it would probably not sound
> very interesting.  The changing phase relationship between the overtones is
> what make a filter sound interesting...IMHO...
> 
> One thing for sure, you will have a difficult time making a filter with
> zero change in phase.  You can make one that has a constant (or near
> constant) time delay vs frequency, but that is about it (time delay and
> phase shift are related)..  Your only hope may be in the digital domain,
> using finite impulse response filters (a subject I am not at all familiar
> with), but even with that, I am doubtful.
> 
> 
> 
> mark s wrote:
> 
>> greets,
>> what are some options for building a state-variable filter with a
>> better-than normal phase response ? what would one have to do to make an
>> SVF that had zero change in phase  (theory or reality) ?
>> 
>> mark
> 
> --
> -Jim
> ------------------------------------------------
> * Visit:http://www.silcom.com/~patchell/
> *-----------------------------------------------
> *I'm sure glad Merry Christmas comes just once a year
> * -Yogi Yorgensen
> ------------------------------------------------
> 
> 
>