Parametric EQ

Written by: Michael Heeley

What is a parametric Equalizer?

To start off this article, there are several assumptions to be made about you, the fine reader.  One, you either record and/or run live sound.  Two, you know what an equalizer, or EQ is, and three, you are curious enough to continue reading since this is going to be relatively technical.  If you have read my other writings, you would know that I attempt to write for the novice, so I will continue to do so, although this subject matter is a more heady than others I’ve written about.  But just in case you don’t know what an equalizer does…

An equalizer, hitherto known as an EQ, allows the user to adjust the gain of a certain frequency either above or below nominal gain.  They are used in all phases of recording, from tracking, to mix, to master.  They are even used by the end user.  The tone knob on a stereo is a single band EQ.  The bass and treble on a car radio is a 2 band EQ.  So, even if you’ve never used an EQ in recording before, if you’ve cranked the bass up on your car stereo to rattle your rearview mirror when the bottom drops, congrats, you have just used an EQ!

This article, however, is about a much more precise, and therefore, a bit more problematic type of EQ called a parametric EQ.  A parametric EQ is different because it allows the user to pinpoint a frequency, adjust the width of the bell curve (Q) and adjust the gain of the frequency, in order to better define the sound of the instrument or voice one is adjusting.

“Not this kind of bell curve.”

The Yamaha O1V digital mixer I used while touring as a sound engineer had a 4 band parametric EQ on each channel and output.  The singer of the band I worked for had a tenor voice that needed a cut at 2.5k hertz (KHz).  For him, a lot of his vocal presence was at 2.5k in most rooms and we needed to adjust that out so he wouldn’t sound so midrangey (I just made up a word).   With an analog board with a 4 band fixed EQ, I would not have been able to pinpoint 2.5k, nor would I have been able to make the Q point narrow enough to not affect frequencies above and below 2.5k.  Instead, I would have had to use the high-mid EQ and high EQ in order to adjust out the throaty sound that his voice made.  Although each mixing board manufacturer is different, hi-mid usually adjusts a range of 1k-2k, and the high will usually adjust 2k-4k.  If I were having to adjust the high eq to help with this situation with a fixed EQ, I would have also been cutting out the frequencies that affect sibilance, which would have affected the clarity of his voice, making it harder for the audience to understand him. The parametric EQ allowed me to hone in on the exact frequency to help his voice sit in the mix.

Parametric EQs come in many different forms.  Some analog and most digital mixers will have a parametric EQ on each channel.  Some analog boards will have a semi-parametric EQ, which may allow you to pin point the peak of the Q (bell curve) but not allow you to adjust how narrow or wide the Q is; meaning you will be affecting a fixed range of frequencies above and below the frequency set at the peak of the Q.

Many of your DAW programs will have some sort of parametric EQ that can be inserted into each track.  They may have a fixed number of bands (3 or 4) or may even allow you to add more, up to as many as you’d like.  This is extremely helpful if you have pinpointed either a standing frequency in your room, or a frequency of the feedback you are encountering.  For example, let’s pretend the room in which you are recording is making it impossible to get a good kick drum sound because there is a buildup of a frequency at 400 Hz, but you still need to boost the low end on the kick track because that is what gets the women out on the dance floor when the track is played at the club.  With a parametric EQ, you can create a shelving EQ at 500 Hz to boost every frequency 500 Hz and below, but then put another point at 400 Hz with a very narrow Q, and cut that frequency out of your shelving EQ, thereby eliminating the problem that the room is giving you.  You are essentially boosting 0-500 Hz, but cutting 390-410 Hz, with the majority of the cut coming at 400 Hz.

There are also many outboard parametric EQs to chose from.  The usual benefit of outboard gear is the construction of the piece.  Since analog gear requires real components, the sound of these pieces can range from hellish to heavenly, depending upon the quality of the components in the piece, the labor to construct it, and the amount of money you are willing to spend on it.  The disadvantage to the analog outboard pieces is the digital versions have pictures of the cuts and increases along the frequency spectrum, so you can see things like how narrow or wide your Q is at a particular frequency.

Well there you have it, a beginner’s guide to parametric EQs  They can be difficult to manage at first, but for the most part, they allow you a better control of your tracking, mixing, and live sound situation.  At the end of it all, however, it requires a good ear to find the troubling frequency, and a solid understanding of the cause/effect relationship of adding or subtracting from a frequency.  A parametric EQ is just another tool in your toolbox to find the sound.  Maybe Kiss should have used one when they were recording Beth.

Equalizer in photo: Manley Massive Passive Stereo Equalizer


Be the first to comment on "Parametric EQ"

Leave a comment