Parametric EQ explained: What is a parametric equalizer?

When it comes to equalizing your tracks, a parametric EQ is one of the most versatile equalizers that you can use. That’s because it offers the flexibility to make vastly different types of alterations to a signal’s frequency response.

With a parametric EQ, you can make very subtle changes to the frequency spectrum, but you can also make extreme ones as well. Similarly, you can pinpoint very specific frequencies to equalize, but you can also make broad changes to large groups of frequencies too.

Because of this, parametric equalizers enable you to make the exact changes to the way an instrument sounds that your mix needs. In this article, I’ll explain what a parametric EQ is and how to use one.

Click here for a video tutorial on using Parametric EQ:

What is a parametric EQ:

A parametric EQ allows you to make a cut or a boost to the frequency spectrum. The frequency response curve created by a parametric EQ is referred to as a ‘bell’ curve, so-called due to its shape. You may also hear it referred to as a ‘peak’ curve. These bell shaped cuts and boosts can be made to your desired gain amount. For example, here you can see a boost of 6dB at 1kHz:

Whereas here, you can see a cut of -9dB at 300Hz:

With a parametric EQ you are able to control not only the amount of gain applied, but also the centre frequency of the cut/boost and also the width of the cut/boost that you’re making. For example, here you can see a very narrow boost of 10dB at 5kHz:

Whereas here, you can see a very wide cut of -8db at 500Hz:

Controlling a parametric EQ:

To achieve these different kinds of equalization, you must control three separate parameters. Those parameters are: gain, centre frequency and bandwidth:

Gain: The gain parameter on a parametric equalizer allows you to control the amount of boost or cut that you are applying.

Centre Frequency: The centre frequency refers to the frequency which resides at the very centre of the bell shaped boost or cut that you are making.

Bandwidth: Bandwidth refers to how narrow or wide your boost or cut is. Bandwidth is usually controlled by the ‘Q’ setting, which stands for ‘quality factor’. The higher the value of the Q setting, the narrower the bandwidth will be. Similarly, the lower the Q value, the wider the bandwidth will be.

Variations:

A parametric EQ which allows you to control all three of these parameters is known as ‘fully-parametric’. But there are some equalizers which create the same kind of bell shaped cut or boost, but offer you less control than that of a fully-parametric EQ.

An EQ which allows you to control only the gain and the centre frequency, but not the Q setting, is referred to as a ‘semi-parametric’, ‘sweepable’ or ‘swept’ EQ. An EQ which offers you control over the gain, but not the centre frequency or Q setting, is known as a ‘fixed band’ or ‘fixed frequency’ EQ. It’s worth noting that the terms ‘fixed frequency’ and ‘sweepable’ are not exclusive to EQs which create bell curves. They can also be used to describe the behaviour of shelving filters as well.

Another variation of a parametric EQ is a ‘notch filter’, known also as a ‘band-stop filter’ or ‘band-reject filter’. A notch filter is a cut at your chosen frequency with a high level of attenuation. Typically, a notch filter has a very narrow Q value and is used for the removal of very specific bands of frequencies. That said, the band of frequencies being attenuated can often be widened via the Q setting on many plugins.

Why use a parametric EQ?

Parametric equalizers offer an unparalleled level of control over the kind of equalization you create. By allowing you to take control over the equalizer’s gain, centre frequency and bandwidth parameters, you are able to make precise EQ alterations to suit the needs of your track. You are able to make changes to large portions of the frequency spectrum, or make very specific, surgical alterations to really fine tune your sound. Such approaches allow you to achieve very specific results like giving an acoustic guitar more body or cutting out a ringing frequency on a snare. The ability to make such varied alterations makes a parametric equalizer an extremely versatile EQ.

Do you use a parametric EQ when you mix your songs? If so, what sort of things do you use it for? Leave your ideas in the comment section below.

Want to know more about EQ? Learn about pass filters here. Learn about shelving filters here. Download your free EQ settings cheat sheet here.