[sdiy] SVF & phase

[Magnus Danielson]

From: "jhaible" <jhaible at debitel.net>
Subject: Re: [sdiy] SVF & phase
Date: Wed, 27 Nov 2002 17:32:11 +0100

> Now let _me_ play the devil's advocate:
> 
> There is a remarkable filter effect that attenuates high frequencies and
> might not result in a phase shift: The reproduction of an analogue recording
> over a mis-aligned tape head (wrong azimuth):
> 
> Questions:
> 
> (1) Does this really cause no phase shift?
> 
> (2) Of course it does *not* go against the above rules, even
>       if it doesn't cause phase shift. Why ?

B'Cause equally amount of early and late signal mix. You get an impulseresponse
which is balanced (i.e. it mirrors around its centerpoint - the peak) and this
satisfies the specific condition for a linear phase resonce. If you design a
FIR filter for linear phase, you actually design in the same mirror propperty
in the filter coefficients. Optimized hardware uses this fact and halvs the
multiplications using this fact BTW. Creating the same situation using analog
curcuits is however a hell, you devil's advocate!

Cheers,
Magnus - who brought back his machine "heaven" from a frozen state earlier