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From: cyamamot@castor.usc.edu (Cliff Yamamoto)
Newsgroups: sci.electronics,rec.audio
Subject: How to minimize phase shift (& what causes it)?
Keywords: phase, shift, parametric, equalizer
Message-ID: <5214@merlin.usc.edu>
Date: 20 Sep 89 18:24:08 GMT
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Reply-To: cyamamot@castor.usc.edu (Cliff Yamamoto)
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Organization: University of Southern California, Los Angeles, CA
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Greetings!

I would like some opinions from those who have used parametric equalizers
before or who know about active filters.

I have a parametric equalizer which I've adjusted using a RTA for my stereo.
It sounds quite good but it still nags me to know that I may be causing it to
sound worse due to inappropriate adjustment.

What I'd like to know is: what actions to a parametric equalizer (i.e. active
filter) cause the most phase shift?  Is it better to have a hi Q and low boost
(i.e. gain) or is it better to have a low Q and hi boost?  Should I try to get
by with the lowest Q possible?

I know a hi Q setting (like Q=10.0) causes the eq to make pink noise sound
as though it were in a wind tunnel; there is a unnatural "hollow" noise.
Knowing that a hi boost and hi Q cause it to sound unnatural, I try to keep
all my Q's and boosts/cuts as minimal as possible.  Is this right?

My actual scenerio is this:  I have to cut -15dB at 800Hz because of some
unusual resonance.  Even with a Q=10.0 it brings down 1.2Khz and 400Hz by -6dB
even though I don't need it to.  On top of that, a -15dB cut with Q=10.0 makes
it sound lousy.  Should I widen the Q and cut by -9dB at 800Hz and boost
everything below 400Hz and everything above 1.2Khz by +3dB?

It seems you could spend hours with a parametric eq, even with a RTA!!

Thanks for any assistance
Cliff Yamamoto