What do equalizers do?

When you use an equalizer, you are basically controlling the volume of a certain range of frequencies.

“Graphic” equalizers have a number of bands that can be controlled individually (like in a “31 band” eq). In that case, you have sliders that give you control over the level of 31 fixed, adjacent (and often slightly overlapping) frequency ranges.

Graphic EQ:

This is the dbx iEQ31 Dual Band Graphic EQ (and Limiter!)

Graphic eqs are often used in live sound, to reduce frequencies that are contributing to feedback. This is often refereed to as “corrective eq”. Of course, graphic equalizers are also used to adjust the overall frequency curve of the mix.

Parametric EQ:
graphic eq

In contrast, parametric equalizers can have their individual bands customized to what the user wants. As with the graphic eq, you can adjust the level of each band, but you can also adjust the center frequency (the frequency at which the eq will boost or cut), and the “Q”, or the width/range of frequencies that will be affected. Parametric eqs typically have less available bands that graphic eqs, but that’s not a problem, because you can set each band to do exactly what you what. The picture above shows the Waves Renaissance parametric eq, part of many of he Waves plugin bundles. This particular version is a 6 band equalizer, because it has a total of 6 color-coded, flexible frequency ranges that can be adjusted as the user sees fit. Note that band 4 (the blue band) has a very narrow, or high, Q setting, so it (in this case) is cutting a very narrow range of frequencies. Band number 3 (the green band) has a lower Q setting, and (in this case) is slightly boosting a very broad range of frequencies.
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