Equalization is always an interesting topic. I have found it to be completely overused in many cases, completely overlooked in other cases, and completely misunderstood in most cases. To illustrate my point, check the settings in a couple different car radios. The controls are either untouched or the treble and bass are completely cranked. Chances are that somewhere in between, the truth lies. Without getting into the finer points of EQ that may well be debated until the end humanity, I will explain what EQ is, give you a few guidelines on how to use it, and explain the four basic types of equalization that are currently standard issu.
The human ear can hear frequencies from 20-20,000 Hz. Within this range are the changes that we make with our EQ devices. Some devices will effect large chunks of the spectrum centered on a specific frequency while others can be quite surgical and exacting. In simplest terms, if you picture all audible sound as a straight dotted line where each dot represents a frequency, equalization is the ability to change the relative volume of the dots individually without affection the others. Below is a chart showing what ranges of the spectrum instruments generally fall into.
The main types of equalization are Fixed, Sweepable Mid, Parametric and Graphic.
Fixed is the most basic in the list. You have seen this on on most every home stereo system in the past several decades. These are the Treble, Midrange, and Bass controls. Each control is anchored on a specific frequency and when active effects the frequencies on either side of it in a bell shape of a specified range. A large group of frequencies are affected, but it is very easy to use and adequate for most consumers.
Sweepable Mid EQ is usually found on higher end mixers and recording consoles. This is similar to the Fixed EQ with one major addition. The midrange has an extra settings knob. This frequency knob lets you pick the precise frequency range that you want. It is no longer anchored like in the fixed configuration. This is especially useful when you really know the frequency that you want to get at.
Parametric EQ is the big boy on the list. This is for complete control of your EQing universe. These days you are very likely to see it as a plug in used by your recording software as opposed to outboard gear, but the functionality is all the same. Taking the sweepable EQ to the next step, you get a Q control. The “Q” is the bandwidth. You can grab a large amount of frequencies with a “wide Q” or just a handful with a “narrow Q” setting. So dial in the frequency, select the Q, and reduce or boost your favorite part of the signal.
Finally we come to the graphic EQ. This is basically a fixed EQ with 31 separate knobs… but since that many knobs on a single rack space would be inoperable for humans, sliders are used. The frequency spectrum is divided equally against the number of sliders. The most common use of this type of EQ will be at the end of the chain of a live mixing board to deal with the acoustics of the room. Far more often than not, deductive EQ is employed in this situation.
Now that we have the types of EQ out of the way and we know more clearly what EQ is… how do we use it? That is a never ending topic that I do not have time to write. I am not immortal. At least I don’t think so. Generally I would say that a little bit will go a long way. Extreme settings will get you extreme results that can be fun for an effect, but likely useless for much else. Also, you can get amazing results not in boosting the frequency that you want, but you reducing the ones that you do not want.
As a final thought, just do what sounds good. Do some experiments. Have fun learning. There are many that will tell you that you always need to add 4dB of 6k to a kick drum, but maybe you do not want that click of a beater in your kick. Just pay attention and listen to what the song needs and you will do what is right in the end and not what you think that you should be doing.
