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From: saf@clyde.UUCP (Steve Falco)
Newsgroups: net.audio
Subject: Re: A Question on Equalizers
Message-ID: <800@clyde.UUCP>
Date: Thu, 14-Feb-85 08:28:07 EST
Article-I.D.: clyde.800
Posted: Thu Feb 14 08:28:07 1985
Date-Received: Fri, 15-Feb-85 03:39:36 EST
References: <2677@sdcc3.UUCP> <1026@hou3c.UUCP>
Organization: AT&T Bell Laboratories, Whippany NJ
Lines: 25

> What is the difference between a "parametric" equalizer and
> a "graphic" equalizer?

A parametric eq in its "absolute" form has a knob for each parameter.
Thus there is a knob for center frequency, Q, and gain (+ or -).  In
actual practice, the cheap stuff usually omits the Q adjust resulting in
a semi-parametric eq.  Naturally, you need several such units in cascade
to fix multiple bumps in your pre-eq response curve.  The advantage is
that you can put the center frequency exactly where you want it, etc.
So you can compensate out any reasonable anomaly (reasonable == within
the range of the filter pots).

A graphic eq has fixed frequency, fixed Q filters where only gain is
adjusted.  Here, many narrow filters are needed to get results
approaching a parametric unit.  This means more phase problems and
interaction between the filters (harder to adjust).  It is also rare
that the filter center frequencies are exactly where you want them.

I don't know why graphic eqs seem more popular than parametrics.  A 3
band parametric (which is usually sufficient) has about 9 pots and isn't
"hard" to build.  A graphic eq might have 10 to 30 sliders plus lots of
precision caps (and even coils - yuk).  Anybody know why there aren't
more good (and cheap) parametric units out there?

	Steve Falco  AT&T Bell Laboratories