What Is EQ?

Eq or equalization is the technique of balancing the frequency spectrum of a piece of audio. A primitive example of this is the bass and treble knobs on your car or home stereo. An equalizer boosts or attenuates a certain range of frequencies relative to the rest of the spectrum and it is one of the most valuable tools in the producer's arsenal.






Types of EQ
There are a few different types of eq tools you may come across, the two main ones being graphic and parametric eq. In a graphic equalizer, the frequency spectrum is split up into sections or bands. Each of these bands has a gain control to boost or cut in that specific range. The range that each band controls is called its bandwidth and this value is generally fixed.

Graphic Equalizer

A parametric equalizer is more flexible. Not only are you able to adjust the gain of a particular band, but also the bandwidth and the center frequency of that band. In other words you can adjust how much to boost or cut, where exactly to do that, and how narrow the range of frequencies affected will be. On a standard parametric eq, the bandwidth will be controlled by the Q parameter. Higher Q settings result in a sharper band, whereas lower settings will produce a wider band.

Parametric Boosts

This image shows two boosts. The first one on the left has a low gain setting and a low Q setting, resulting in a broad gentle bump. The second boost has more gain and is sharper due to a higher Q setting.


Most parametric eqs will also include shelving filters and pass filters. These both work on everything above or below their center frequency.

Low and High Shelf Boosts

Here we have two boosts, the first with a low shelf, the second with a high shelf. Notice the low shelf boosts or cuts everything below its center frequency (the green dot) while the high shelf affects everything above its center frequency. As with the bell shaped curves, you can use the Q control to set how gradually this change occurs.

High Pass and Low Pass Filters

In this shot, we've got a high pass and a low pass. These completely filter out everything above or below their frequency. The high pass lets all the frequencies above it pass, while the low pass does the opposite. These are also referred to as low cut and high cut. Try not to get confused here, a low cut is the same as a high pass and vice versa. Again, the Q controls how sharply they drop off. If you were to switch the positioning of these two filters you'd end up with a big valley in the mids where no sound gets through. Only the lows and highs would be audible.


These are the essential tools to shape the spectrum. The average track will probably use equalization on each instrument and each eq will probably have several bands working at once to get things balanced. In an ideal world, you'd never need to use eq because everything you recorded or synthesized would fit perfectly into the rest of the mix. That's a whole different discussion, but needless to say this is rarely the case; Some type of equalization will need to be applied to make things stand out and prevent frequency clashing.

In the next article, I'll explain common situations where eq is needed and some techniques to apply it.