Basically, it boost’s or lowers the volume of certain frequencies.

Definition: Equalization (E.Q.): “An effect that allows the frequency-selective manipulation of a signal’s amplitude. The simplest equalizers are shelving types, offering the ability to cut or boost gain above or below a given frequency. Equalization doesn’t only change the level of specific parts of the audio spectrum, it also changes the phase of the affected frequencies relative to those that aren’t being E.Q.’d i.e., E.Q. affects both the frequency response and phase relationships of a signal.”

Audio Spectrum: “The range of frequencies present in a waveform, such as an audio signal”. On the last page a diagram is given to show this spectrum.

Shelving types: shelving refers to the ability to boost or cut a certain frequency and then all the frequencies beyond that, either at the top or bottom of the spectrum (see illustrations below)

E.Q. Hi Shelf	E.Q. Low Shelf

Shelf Depth Refers to: the illustration below

E.Q.’ing should be your last line of defense. Microphone positioning is a better solution to frequency problems (or just finding a better sound).

For instance, next time you Mic an acoustic guitar, put your head in and around where the player is and notice how the sound changes. Up near the neck you get more of the string sounds and it’s a bit thinner. As you travel down near the sound-hole and at the tail of the guitar, high frequency falls off and you get more lows. Where your Mic is placed determines how it will sound.

Keep in mind that you’re listening in stereo, if you put one Mic up and expect it to sound like it did when you were standing by the Mic, you’ll be disappointed. Put up two Mic’s to get that fuller stereo sound. Keep the channels left and right separated or if you want bus them to a track if you like (we will go over bussing later).
Now that we have discussed some definitions of an E.Q. what types of E.Q.’s are there? There are 3 types of E.Q.’s you will most commonly find on a console.