EQ for Dummies
You’re probably wondering; why this post should be any different than any other post online about EQs!!
In this post, I will break down the basics of EQs, we’ll talk some brief history, treminology, filter types and functions along with guidelines on best practices.
Equalization is to adjust or alter the balance between frequency characteristics within an audio signal, although the term is also used in electronics and telecommunications as well; we will focus on recording production for the purpose of this post.
Most common EQs in production are :
Parametric : They allow for more complex adjustments like Cut/Boost, Primary/Center Frequency and Bandwidth/Range.
They offer precision and flexibility - especially when surgical adjustments are needed; they are suited for fine tuning and shapining characteristics of specific frequencies with minimal without affecting others too much.
Graphic : Simpler type than a parametric EQ, common types are comprised of multiple sliders that cut/boost specific bands, the number of bands available will vary from one make or model to anothe.
One very important thing to note about a graphic, the bandwidth/Q is adaptive depending how much you cut or boost, so the more you boost or cut the wider the Q is; therefore when you adjust one slider - you are also affecting upper/lower neighbouring frequencies.
The terminology of EQs was applied to correct frequencies of phones lines through a passive network.
A Brief History
Equalization dates back to multiplexing and telegraphray, initially filters were incroporated in Pro Audio gear to be used in the broadcast industry; the very first filters had only 2 basic bass and treble controls. John Volkman was the first to use variable EQs in the 20s.
The EQ-251A by Langevin was the first to use slide contols with dual passive sections.
The 7080 was the first Graphic, it was developed by Art Davis who later on built the Model 9062A EQ, Davis also developed the first 1/2 octave variable filter set called “ Acoustic-Voice”.
The first sweepable parametric was introduced in 1971 by Daniel Flickinger, using high perforamnce Op-Amp to acheive filtering circuits, later in 1972 George Massenburg introduced another similar design and coining the term parametric EQ which was presented at the 42nd AES convention.
Later in the 1990s and 2000s parametric EQs became widely available as DSP units in plugins…etc.
The theory of linear filters governs EQ functions, however the functions and how flexible they are is governed by the design ( circuit topology) plus the user defined controls.
In Signal processing, there are many different classifications of filters; which we will visit at a later stage.
High Pass : It passes high frequency and cuts low ones below the cut off point, commonly used to cut very low rumble and hums
Low Pass : A low pass filter passes low frequency and cuts high ones, commonly used to remove hiss noise; caution advised not to too much high end of the signal.
Peak : A peak filter allows you to cut/boost around the centre frequency, also has an adjustable Q point which determines how wide the region around the cut off point will be.
Shelving : Shelving EQs are used to cut/boost above or below a set of frequency, commonly used as tone controls, they implement a first order response and provide an adjustable cut/boost to frequencies higher or lower a certain point.
High shelf will cut/boost the cut off frequency and anything higher than the set cut off point, commonly used in high mids to high range.
Low shelf will cut/boost the cut off frequency and anything lower than the set cut off point, commonly used in low to low mid range
Filter response is described in terms of it’s transfer function or it’s response for a possible input, in other words the trnsfer function describes the filter behavious. A transfer function can be broken down as a combination of first and second order responses.
First Order can modify the frequency response above or below a certain point; with a slope of 6 dB per octave for the transition area, it’s the simplest of all which can be implemented as stand alone and require minimal components.
Second Order filters can control the resonance at a particular frequency, the response of this type of filter is specificed by it’s Q function frequency, a higher Q means a tighter sharp response around the centre frequency and vice versa.
It’s important to note that a second order filter with less than 1/2 an octave of Q can be broken down into two first order filters.
Parametric EQ sections directly implement a number of second order functions, Graphic EQs are based on filter banks whose Qs aren’t adjustable by users.
So now you got your history and terminology in a good place and you’re thinking so now what!!??
If you reached out for an EQ then you am using it for one of the following ( correcting or complimenting a signal, making more space in the mix, special FX)
Keep your goals and priorities straight when you are choosing what to EQ and which EQ you are using.
Cleaning up a signal :
Sometimes, the takes you have were not recorded perfectly ( happens more than you would imagine), reach out for an EQ to clean up the source and get the balance you are looking for from that particular track.
Tip : I would use a transparent EQ for this task, having a colorless EQ at your disposable is one of the most important thing to keep in mind while mixing.
Tone and definition : once you have corrected and cleaned up your source, then review and make sure the tonal balance between other tracks is still intact, remember we are complimenting the music and the feel of the song.
Tip : I would use an EQ with character, particularly one with harmonic distortion that will compliment the source, think tube EQ or vintage console.
Special FX : whether it’s a dynamic type filter or a mid range focused sound, it happens quite often that there is a specific sound that
Tip : Use a versatile one with enough complexity that enabls you to do whatever you want with the signal, note that the more complex it is the more time you’ll spend figuring it all out.
EQing is one of the skills that will improve upon repitition, so keep doing it - your decision making process will improve and your mixes will sound much better.