rs@hou3c.UUCP (Bob Switzer) (02/13/85)
<> What is the difference between a "parametric" equalizer and a "graphic" equalizer? A friend of mine bought a reel-to-reel tape deck, and the guy at the shop he brought it from told him something to the effect that you should *always* use a parametric equalizer for recording. This sounds like a snow job to me, but I would still like to know what this thing is. Thanks, -- R. Switzer @ AT&T Bell Labs Rm. 3L-434 / Crawford Corner Rd. Holmdel NJ 07733 phn:1(201)949 5133 ...!hou3c!rs
rfg@hound.UUCP (R.GRANTGES) (02/14/85)
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In the usual octave band equalizer, the boost or cut curve vs frequency
of each part of the spectrum is fixed, you determine its amplitude by
setting a sliding control. So, for example, one of the sliders may
represent a boost or cut centered on 500 hz. By adjusting the control
you set the response at 500 hz between -12db to + 12 db of flat, or
anywhere inbetween. When you have the control set for , say, +6 db at
500 hz, you can then only change the response by similarly adjusting
controls at other fixed frequencies - usually octave related like 250 hz
and 1000 hz. This gives you a lot of control, but not always just the
control you want. You may be wanting to notch out a tone at ,say, 750 hz.
You can cut 500 and you can cut 1000 but you have cut a wide band of
frequencies in order to affect 750.
A parametric equalizer gives you (usually) continuous control over three
"parameters" of the tone curve for each correcting unit supplied (usually
at least two independent units are supplied (per channel) but sometimes
4,6 or more). Anyhow you can control the center frequency of the tone
shape, the degree of boost or cut at that frequency, and the shape of the
curve with frequency ("Q" of the filter to those who speak that way) -
whether the control curve is narrow or wide. Hence, to return to the
previous example, with a parametric equalizer you could tune it to 750 hz
set it for narrow band attenuate and notch out the offending tone
without affecting much more of the spectrum. (Ignore phase effects as I
suggested in a previous article, they just needlessly worry you.)
Which is best is a question much mooted about. For relatively mild effects
extending over moderate amounts of the spectrum, perhaps an octave band
equalizer (or "eq") is best. For specific control over very limited parts
of the spectrum, like notching out a resonance or hum, a parametric is
best. Para's are also god for mild actions affecting broad sweeps of
spectrum. With a para, unless you have a lot of units, you can't make up
a very complex curve. Para's are not found very frequently these days and
tend to be expensive. There are many cheap octave units on the market,
some of which may be ok.
--
"It's the thought, if any, that counts!" Dick Grantges hound!rfgherbie@watdcsu.UUCP (Herb Chong [DCS]) (02/14/85)
In article <1026@hou3c.UUCP> rs@hou3c.UUCP (Bob Switzer) writes: ><> >What is the difference between a "parametric" equalizer and >a "graphic" equalizer? a graphic equalizer just has adjustments for the level of boost or cut. the frequencies at which these take effect are fixed and so is the Q or "wideness" of the band of boost or cut. a parametric equalizer allows you to adjust all three, giving you much more control over the frequency curves that you can create. they are more flexible and are more likely to be found in recording studios than homes. with the increased control, you will find fewer level controls than a typical graphic equalizer. i personally favor getting a parametric over a graphic provided that it is a good one and you really can use one. >A friend of mine bought a reel-to-reel tape deck, and the >guy at the shop he brought it from told him something >to the effect that you should *always* use a parametric >equalizer for recording. This sounds like a snow job to me, >but I would still like to know what this thing is. i don't believe you ALWAYS need one, or even that you need one most of the time for recording, but if you are serious about live recording, then having one sure is handy. >Thanks, >-- >R. Switzer @ AT&T Bell Labs >Rm. 3L-434 / Crawford Corner Rd. >Holmdel NJ 07733 phn:1(201)949 5133 >...!hou3c!rs Herb Chong... I'm user-friendly -- I don't byte, I nybble.... UUCP: {decvax|utzoo|ihnp4|allegra|clyde}!watmath!water!watdcsu!herbie CSNET: herbie%watdcsu@waterloo.csnet ARPA: herbie%watdcsu%waterloo.csnet@csnet-relay.arpa NETNORTH, BITNET, EARN: herbie@watdcs, herbie@watdcsu
saf@clyde.UUCP (Steve Falco) (02/14/85)
> 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
peters@cubsvax.UUCP (Peter S. Shenkin) (02/21/85)
A parametric equalizer is one which, for each stage, has three continuously variable pots: one for frequency, one for dB of boost or gain at that frequency, and one for sharpness of the band around the frequency over which the boost or gain will apply. A typical parametric equalizer will have four bands, for bass, low-mid, high-mid and high frequencies, and the frequency controls on adjacent bands generally have quite a bit of overlap. The central bands give a boost or gain contour with the general appearance of a gaussian (I'm sure you EE's know what it really is; perhaps a Lorentzian?), and the outer bands usually give the same, though these are sometimes set up with a shelving contour, in which case the band-width control really refers to sharpness of roll-off or "roll-on". Parametrics are very versatile, and I don't doubt that many recording engineers prefer them for "eq'ing" vocals, for instance. But I'm sure that many would take issue with the idea that they are *necessary* in the recording process. Peter S. Shenkin cubsvax!peters (Columbia Univ. Dept. of Biol. Sciences)