I meant to say parametric, sorry about that.
http://www.prorec.com/prorec/articles.nsf/files/4944E23A057D188D862565F4005D82B3
This explains it much better than I could. I use all three sometimes, depends on what I'm going for. Parametric get the most realtime play for me inside Vegas though
Fixed EQ
This is the type of EQ you’re likely to find on the vast majority of home hi-fi preamps, and on the channel strips of the cheapest mixers. Here, you only have the option of controlling “how much” -- the “what” is fixed and is not adjustable.
These usually consist of two or possibly three rotary pots. The high (or “treble”) and low (“bass”) knobs are generally shelf-type filters with fixed cutoff frequencies (usually at about 100 Hz and 10 kHz or thereabouts) and pretty generous slopes. The “mid” control (if there is one) is a band-notch filter with a fixed center frequency and bandwidth, usually at least a few octaves at around 2 kHz or so.
Needless to say, this is the least flexible of all the types of EQ, and are good for little else except very broad tone-shaping.
Semi-Parametric (Sweepable) EQ
This is a major step up from fixed EQ. While the bandwidth is still fixed, the center frequency can be adjusted; usually along a very wide range. This is what you’ll usually find on nearly any decent, mid-priced mixer. For example, the channel strips on a Mackie 1604 has fixed high and low controls, but a semi-parametric mid-band control.
This is a great tool to have, as the ability to pinpoint a specific frequency has tremendous advantages. Try this trick sometime -- if you are trying to hunt down a specific frequency on a track (such as the attack on a guitar, the snap of a kick drum, or the beefiness in the bass), run the track through a semi-parametric EQ and boost the gain control full up. Then sweep the center frequency s-l-o-w-l-y from its lowest to highest point. If you listen carefully, the frequency you’re seeking should jump right out at you! Once you’ve found the desired frequency, then back off on the gain control, adjusting it to taste or as necessary to achieve the desired result.
Parametric EQ
This is the most adjustable and flexible type of EQ, and can pretty much address almost any EQ task. With a parametric EQ, gain, frequency, and bandwidth can each be adjusted on its own, independently of the others. The sweeping trick discussed above is often used with parametric EQ, with the added advantage that the bandwidth can be set up to affect a very wide range of frequencies around the center, or a very narrow range, depending on your needs and the specific application. With a parametric EQ, you can do some powerful and very specific tone coloring. If you refer back to Part One of this article, where I walked you through some EQ mixing fundamentals, you’ll see how useful a parametric EQ could be for this purpose -- with total and ultimate EQ control right at your fingertips, making the pieces of a mix fit together is much, much easier and far more effective!
The more expensive and nicer recording consoles usually have at least one band, and sometimes two or more overlapping bands, of parametric EQ -- if not on all channels, then at least on some of them. Of course, not everyone has the luxury of working on one of these babies. If not, I strongly recommend that anyone truly serious about recording get their hands on at least one -- if not a couple -- of top-notch, outboard multiband parametric EQs. Be warned; the good ones (really, the only kind worth having, right?) are not cheap; but the flexibility, control, and incredible array of EQ options you’ll have at your disposal will be worth it.
Graphic EQ
This is the type of equalizer that is familiar to most people, and is the easiest and most intuitive to operate. It is somewhat similar in operation to fixed EQ in that bandwidth and center frequencies are fixed, but instead of having only two or three rotary controls, it sports many sliders (usually ten or more) at many different frequencies spaced evenly across the audible frequency spectrum. The range of boost or cut possible is usually at least +/- 12 dB, but better units can go +/- 18 dB or even higher. Just by looking at the slider controls on an graphic EQ, you can pretty much tell what the resulting EQ curve looks like.
The bandwidth of each slider control on a graphic EQ is dependent upon the number of sliders it has. A graphic EQ is set up so that it reaches from the lowest to the highest point in the spectrum. As we said earlier, the audible spectrum is about ten octaves wide. So, if we have a graphic EQ with ten sliders on it, what would the bandwidth of each slider be fixed at? Hmmm... this is a hard one, eh? Take your time. Okay.... time’s up! The answer is that each slider has a one octave bandwidth. No duh.
Here’s your extra credit question: if you wanted to build a graphic equalizer that could provide even more precise control -- say, a one-third octave bandwidth for each slider -- how many sliders would you need? Did you say “thirty?” WRONG! It’s actually thirty-one! Traditionally, EQ manufacturers sneak an extra slider into the one-third octave graphic EQ, which allows them to effectively cover just a little bit more ground than you usually can with a ten-band EQ. The 31-slider configuration is pretty much an iron clad standard -- you will not see a thirty-band graphic EQ anywhere, trust me on this.
Besides one octave (ten-band) and one-third octave (31 band) graphic EQs, you’ll occasionally run into a 15-band EQ out there. If you’ve been paying attention (hey you in the back, face forward and be QUIET!) you should be able to deduce that each slider on a 15-band EQ would have a bandwidth of two-thirds of an octave.
Paragraphic EQ
With the advent of digital display technology and computer-based recording and processing, it has become possible to combine many of the best features of both the parametric and graphic equalizer. This has brought us the relatively recent hybrid beast that we call the paragraphic EQ. The paragraphic EQ doesn’t differ a single bit from the parametric EQ in terms of sound, controllability, or flexibility of purpose; but only in the way the user interfaces with it.
Traditionally-designed, hardware based EQs are pretty much limited to the use of real-world, tactile controls -- buttons, knobs, dials, and what not, that you can physically grab with your fingers and twist and tweak to your heart’s content. There’s a lot to be said for this; however, it has its drawbacks, too. With a parametric EQ, usually consisting of an array of knobs, you don’t receive much visual feedback as to what you’re doing -- as you change the settings, the sound changes, but the knobs just sit right there. The sliders on a graphic EQ provide a much better visual representation of the EQ settings you’ve made; but still, bandwidth and frequency for each slider is fixed, and there are other, physical limitations as well -- for instance, you can’t move the sliders around, or make them appear in a different order if you want to.
However, with software-based EQs and EQ plug-ins -- and increasingly, on outboard units with digital control via LCD screens and the like -- these physical limitations don’t apply any more. The sky is pretty much the limit here -- using the powerful graphical interfaces possible on today’s computer displays, it’s possible to make EQ controls pretty much look like whatever the developer dreams up. Many of the cleverer companies out there have taken advantage of this to create EQs that still contain all the power and control of a parametric EQ, but that present an intuitive look and feel, much like a graphic EQ.
. BANG BANG!
thanks for the ideas fellas