EQ helps your audio sound better and corrects problems when recording. You can even use it to create special effects.
How can it do all that? Let's take a look at what audio is made of; the building blocks of sound.
When you hear different pitches in music, you are hearing sound waves in different frequencies, or speed of the waves. A high pitched note comes from high frequency sound waves. Low pitch means a slower wave.
The frequency range that people can hear is approximately from 20 hertz to 20 kilohertz (abbreviated Hz & kHz). An average person can hear most of this range, but usually not the extremities. Normally, 40Hz is the low end and 16kHz the high end of a healthy human ear.
Most microphones take advantage of this by having a frequency response of 20 Hz to 20 kHz.
When you hear an A on the piano, you are hearing sound waves at the fundamental frequency of 440 Hz. This simply means the base, or the most important, is 440.
But you guessed it, there's more!
In addition to the fundamental frequency, a lot of other frequencies work together to give the sound character. These are called overtones. Simply put, overtones work in concert with the fundamental and make each sound distinct. Overtones are the reason we can tell the difference between a piano A and a guitar A.
You know how you can usually know who is calling on the phone, simply by hearing their voice? You're hearing their overtones.
Why do we need to know this to work with EQ?
Mics usually color the sound they record. Color simply means that they pickup some frequencies better or worse than others. A good mic will not color much at all, but some are worse.
This "coloring" is not all bad, though. High end mics are designed to give a nice smooth sound - they can color your music so it sounds better.
But sometimes this coloring that happens is not what you want. Whether it came from inside the mic or mic placement, things can go wrong.
So when you record several audio tracks and mix them together, you can multiply the problem. You now have something you don't like. How can you fix this?
That's where the whole equalization thing comes into play. It lets you change certain frequencies while leaving the rest alone. In this way, you can go in there and tweak the certain spots that need fixing. Then you have a better finished mix!
If you've ever tried this, you know that this is a lot easier said than done.
I'll try to explain roughly how the different frequency ranges impact your sound.
I record a lot of a cappella music, so you may find a few differences with instrumentation added. (A cappella means no instruments)
40Hz is usually as low as most good speakers can make sound at, so it doesn't make sense producing anything below that. The very bottom bass notes are down close to here!
If you have any trouble with your mix clipping, but it doesn't seem too loud, try cutting around 150-200Hz and lower. If that helps, you had a case of low end build up. That comes from a bunch of tracks with excessive low end sound, when it feels kind of boomy.
(If any of this sounds foreign, get the basics on using a parametric EQ.)
On voice tracks, I've found that you can take away some harsh edge by cutting the 1100-1500Hz area. Don't overuse this, because too much can sound pretty fishy!
Try it. I'll wait. Cut around 1100Hz by 20dB. See how bad (or cool) it sounds.
Another range to check out on vocals, especially choirs, is 2-3kHz.
The vocals tend to come out a little more if you boost slightly at 5kHz or so. This brings out the upper end of the frequency range. Also try experimenting in the 8-12kHz range. Be gentle though, too much here will show up quickly!
OK, now we discussed some freqency specific things. Let's move on to some higher level stuff again.
Conventional wisdom will tell you about the "rules" - what you can and can't do. Get ready, because I'm going to tell you something completely different! You may want to sit down...
What! No rules! How am I going to get anything done?!?
Slow down a tad! I said no rules, but there are some guidelines. You can't really "break" any rules when you're doing this, but if you follow the guidelines you can get somewhere faster.
As you experiment with these guidelines, you will be learning far more than if I just told you what to do. You won't just blindly copy instructions. You will see for yourself what happens, and you will retain it far longer.
So - rule #1... sorry, guideline #1:
Keep it subtle. Don't do any drastic changes.
Unless your dry (unprocessed) audio is very bad, you shouldn't have to do anything major unless you want a weird effect. If you find yourself doing big changes (like 8dB or more of cut or boost), stop. Come back after a break and see if you still think it needs it.
Guideline #2: Find the Frequency
When you hear something you don't like in your mix, find what's going wrong. Boost the frequencies in a band of EQ, and "sweep" around to find the frequency that is causing the problem. When you find it, the problem will seem to "jump" out, because you are boosting it. Then, just give it a gentle cut.
After you do this a couple of times, you will learn a lot about working with EQ. Experience is the best teacher.
If something seems lacking in your mix, put a gentle boost on. Do the "sweep" thing again until you find something that works. Alternatively, do a gentle cut and see if there is a spot where you hear a change.
Don't give up trying. When you find the problem after a hard search, you will remember that for a long time. It will become part of your toolkit.
Go try to take away that boomy sound. When you succeed, you will remember exactly how you did it.
You've heard me talk about boosting and cutting, or sweeping. What do these mean? I'm speaking specifically of a parametric EQ, a powerful tool. I highly recommend you use one.
You can also check out a graphic EQ.