What Is A Parametric EQ?
We all have played with simple equalizers before. Every car stereo made since I've been alive has a bass and treble control. These Eqs are quite simple, by design, and wouldn't be that useful for recording engineers in most circumstances so they came out with the parametric EQ.
Basically, a parametric EQ allows you to choose how much boost or cut you want to make (like a typical graphic EQ you've probably used), choose the exact frequency you want to manipulate (which you may have not done before), and choose how wide you want the cut or boost to be. When I say “wide”, I mean you can control if you want to boost 100Hz and also boost 50Hz and 200Hz quite a bit or maybe you want to boost 100Hz and totally leave 85Hz and 130Hz alone.
You can read more about the definition of the parametric eq in the music glossary.
What Can A Parametric EQ Do?
A few common uses of a parametric Eq the following:
High pass filter – Like a crossover this filter knocks out everything underneath the frequency you've selected. If you set this to 100Hz everything under 100Hz is gone. This is very useful on instruments that don't want in your subwoofers. There is often low end energy in a vocal (usually on pops that you don't want anyway), acoustic guitar, electric guitar, keyboards, etc. Sometimes this energy is good, but sometimes it causes real problems when you mix in a big kick drum and big, thick bass guitar. So we knock off everything below a track. Personally, I use this quite a bit. I have no use for my acoustic guitars in subwoofers.
I also use the high pass filter at a much higher frequency when I'm going for the telephone vocal sound (which seams to make it's way on just about every album I do).
Low pass filter – The low pass filter works just like the high pass filter, but cuts everything above a given frequency. If we select 5Khz, everything above 5Khz is gone. We we select 100Hz, everything above 100Hz is gone (not a typical setting).
I don't use a low pass filter that often, but is there if I need.
I also use the low pass filter to make the telephone vocal sound. (I'll knock off everything under 1Khz and then knock off everything above 3Khz....give or take) using both filters to leave only some of the midrange in tact.
Low shelf – A shelf is an eq filter that starts at an extremity and works it way toward the frequency you choose. A low shelf starts a frequency you can't even hear because it is so low and stops wherever you tell it to stop. From there, you can boost or cut as you please. This is a great choice when you want to boost or cut the overall energy in the low end on a kick drum, bass guitar, etc. Sometimes it's better to boost the entire low end than just specific frequencies (which we'll get to in a minute).
The low shelf is very useful when you want to contain the low end in an instrument, but you don't want to cut all of it out. If you were dealing with really muddy electric guitars, you may be able to get by using a low shelf cut up to the point where the mud reduces. (Note: EQ should not be needed on most guitars. I have a rule that if I've used EQ on especially electric guitars, I've screwed up).
High shelf – The high shelf works the exact same as the low shelf but starts at the highest frequencies and works it's way down. If you want brighter drums, a high shelf is a great way to boost the high end overall on that track or bus. If your guitar tracks are too bright overall, a high shelf cut can help.
Many times a shelf is not going to fix specific problems in a track. When a shelf doesn't do what you want to do, it's time to use the standard boost and cut that parametric provides as described above.
So How Do You Know What To Boost / Cut?
Well, this is kind of like telling someone how to hit a baseball in an article. Uhh...swing and keep your eye on the ball. Of course this is useless talk in an article as I'm not there looking over your shoulder. However, I do have a tip.
Let's take a track that has a problem. Let's say the drums sound boxy. (They don't crack, they sound like you hit a card board box. This is very common problem with home recording guys recording poorly tuned drums in terrible acoustic spaces). Now, EQ is not going to completely solve this problem of boxiness, but it can sure help reduce it.
So what frequencies do we need to cut in our drums? Good question.
The easiest way for beginners (and even very advanced engineers) to find a problem frequency is to take a parametric EQ and boost the signal a crap load. Make sure the Q / bandwidth/ width is not set too wide. We want to boost a fairly narrow frequency band. Now, with the track playing, start low and sweep up until you find your problem area that you didn't like before. In other words, keep moving the frequency upward until you the spot where the drums get even more boxy.
Now, instead of boosting a bunch, start cutting. How much, you ask? Bad question. It's a bad question because there is no way a person online can guess how much you need to cut the boxiness out of your drums. If you have a problem, it could be 1dB or it could be 20dB. It's different every time depending on a million factors.
Only Use EQ When You Need EQ
EQ is used to fix problems in a track or enhance a certain quality of a track. It's also useful for making many tracks fit together where they don't compete for the same frequencies. (Example? Listen to acoustic guitar in the middle of a rock song with drums, bass, electric guitars, and vocals. How boomy is that guitar? In fact, when you listen, you may notice that it sounds super thin. This is okay if it works in context with the song. A boomy acoustic guitar doesn't play well with song that already has a lot of “boom” to it.
Back to the topic at hand, DO NOT use an EQ simply because you can. EQ doesn't make tone. You can't EQ an Behringer guitar amp to sound like a vintage Marshall or Fender. EQ doesn't change the character of the track, it just boosts or cuts the frequencies in it.
Modern recording software gives you way too much EQ power in my opinion and it's easy to think you need to use the EQ that comes on every channel. Never use EQ unless you have a reason to.
A parametric EQ is just a wha pedal...sort of. A wha pedal has a set amount of boost. When you push down on the wha pedal you are changing the frequency that is being boosted. Don't believe me? Take a track you have recorded, boost a fairly narrow band by 10dB, and start moving the frequency up and down the full spectrum. It's a very similar effect. I'm not saying that an EQ is not effective. I'm simply stating that an EQ is only going to do you so much good.
Parametric EQ is an extremely powerful tool in your arsenal when not over used. The ability to find a specific frequency is extremely useful in recording. It's something that a graphic EQ will never be able to do. When you throw in the the shelving, hi pass, low pass, and the ability to adjust the width you can drastically alter you tracks (for better or worse) and solve (or create) all kinds of problems that would have otherwise been impossible.