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The Fundamentals of EQ

by | Master Your Craft, Mastering

Equalization (EQ) is one of the essential elements of mixing music, and who knows where or what live, and recorded audio would be without it. Every one of us should have at least heard the term “EQ” whether we know much about it or not because it’s one of the most commonly applied processes of them all. However, whether you’re using multiple EQs on every single track in your mix or you’ve developed an interest in music production, this article will have something for everybody. 

Before we look at some EQ applications, we’ll explore sound a little bit further to understand the basic concept behind it. As most of us know, sound energy propagates in waves that travel outward from the source in a vibrational manner through elastic mediums (anything that can vibrate and transfer the energy). When we start talking about frequency, we’re taking a further look into the characteristics of sound waves. 

You might have noticed that the EQ’ bands’ or frequency spectrum stretches from 0Hz to 20000Hz (20KHz), and this is because this is the general human auditory zone of distinguishable sound for us. Other animals can hear frequencies much higher up the spectrum, but we’ll focus on human hearing now. Let’s take a look at the characteristics of specific frequencies. 

We’ll start in the low-end with bass frequencies as these are the biggest of them all – this is pretty self-explanatory, but let’s dive into more detail. Essentially, the lower the frequency, the longer the soundwave, and the higher the frequency, the shorter the soundwave. Sound will move away from the source at the same speed. However, depending on its frequency, it will complete a wave cycle a certain number of times (Hertz/Hz = cycles per second). With this being said, low frequencies are much longer in length and complete fewer wave cycles per second than higher frequencies which complete many more wave cycles per second. 

Look at the low frequencies, which generally range from 20Hz-250Hz compared to the high frequencies, which range upwards from 1000Hz – 20000Hz (1KHz – 20KHz) – there is a clear difference in how many wave cycles per second there are in the low-end when compared to the high-end. This is why there’s always a call for clarity in the low-end because the sound waves are so ‘big’ that not a lot of stuff can happen in that region at any one time as there isn’t enough space. However, as we move further up the frequency spectrum, soundwaves become ‘smaller,’ which means there is more space for a number of sounds. 

In most songs, regardless of genre, the low-end is taken up by some resonating bass instrument and the transient of the kick drum, but as we move further up the spectrum, we begin to see more instruments occupying the ranges. Take the mid-range, for instance (250Hz-1KHz), where we can find various sounds from instruments like guitars, keys, synths, vocals, and more. Hopefully, this basic run-down has helped illustrate EQ’s concept further, and we should be able to get into the good stuff now. 


For getting this far, here is a reward in the form of an elementary cheat sheet that will help with terminology and visualizing the spectrum.

Freq 20Hz – 130Hz 130Hz – 500Hz 500Hz – 2KHz 2KHz – 8KHz 8Khz – 20KHz



  • This is the region where you’ll find your subs, bass, and kick.
  • There needs to be a lot of room here; otherwise, you’ll encounter boxy, unwanted sounding low-end. 


  • This is a touchy area because it can very easily sound muddy with an overload of sounds. 


  • This is where most instruments sit in the mix. Humans are very susceptible to frequencies in this range because it’s around where our voices sit (human speech is very intricate).
  • You can’t overdo it, though, because you’ll lose a lot of clarity in your mix.


  • A lot of harmonics sit in this region, and if you get it right, you’ll have definition and presence in your mix, but if not, it could sound either dull or harsh depending on your balance. 


  • This is a very delicate region because it can be sharp and fatiguing if it is overpowering, which isn’t ideal for a listener. 
  • If you have too little in the mix, it can sound darker or distant. 

It’s essential to get familiar with these ‘regions’ because there is a pretty universal way of doing things when mixing. After all, it’s all about balance. With that being said, every single mix will be unique, but it’s all about determining how many of what elements need to be present to achieve the perfect balance. You might think it’s all in the ears, but there is a lot of science behind it, too, and the ears will become reliable tools once we’ve developed excellent listening skills. 

If you look at a frequency analyzer of one of your favorite (popular, successful) tracks, you’ll notice a distinct shape that is much more prominent in the low-end region and less so in the highs. If you do the same for any successful track, you’ll notice a very similar shape. This is where the previous paragraph ties in because no matter the song, it can either be well-balanced and sound pleasant to everybody, or it can be either too much or too little, which have separate effects on the song. 

Now that we have a rough understanding of the frequency spectrum, we’re going to look at Equalization and how it is used to create a well-balanced mix. 


Now that we’ve explored frequency in more depth, we can start looking at EQ and why it’s used. As we’ve gathered throughout this article, soundwaves all have unique characteristics, and the low-end frequencies have much bigger waves that have a longer wave cycle compared to the high-end frequencies. This comes into play now as we start looking at ways to treat these individual frequencies. 

Below is another graph to help you along, but this one aims to express the positive and negative outcomes of the various frequency ranges. Think of it as a generalized EQ cheat sheet.

Freq (Hz) 20 – 40 – 80 – 130 – 250 – 500  – 1000 – 3000 – 8000 – 20000
Good Solid Thump Thick Fat Warmth Presence Clarity Bright Air
Bad Rumble Boom Bulk Boxy Muddy Piercing Harsh Sibilant  Crisp


If you were to load all of the tracks into a mix session that was recorded without processing treatment, you’d probably be met with a very loud and overbearing mess of noise. You’ll most likely be able to hear everything, but it won’t sound anything like a finished product that’s ready for distribution. A good mixing engineer will initially work on the levels of every track to get a rough mix that sounds better. The next thing will be to apply EQs (this can happen simultaneously with the leveling) to create space and ensure that every track has been cleaned up. 

Equalization is the process of either boosting or cutting specific frequencies on a given track, group, bus, or master channel. This can be done in a number of ways, from using either a high-cut or a low-cut filter to cut out entire regions, notches to specify regions for boosting or cutting, or shelves to drop and raise entire regions. Essentially, EQ is either ‘additive’ or ‘subtractive,’ but subtractive is probably going to be the most common one you’ll use – let’s find out why.

As you’ll hear, if you had untreated recordings in a new session, it’s a mess. A lot of cleaning up needs to be done to establish some clarity before we dive in with any other processing or creative processing, and this is why it’s mostly subtractive EQ that will be used. Remember – you always need to leave headroom when mixing (at least 3-6dB under 0dB), so most of the time, you’re turning things down or cutting things out. When you’re adding frequencies, you need to be pretty sure about the region you’re treating and be able to have a clear mix already established beforehand so that you can hear whether the effects are desirable or not (too much or too little of anything is out of balance and has negative effects on the mix).


Equalizers and filters will be the processors of choice in most cases when adding frequencies or subtracting them. These two devices do similar things, but equalizers will probably be your most commonly applied one between the two. 

In the next article, we’ll take a look at some great plugins – both free and paid – that are awesome to have in your arsenal as a mix engineer. At the end of the day, though, it’s essential to know how to use them first, so hopefully, this will help initiate the willingness to learn and practice further. 


Knowing what we do now, it’s essential to make sure that the low-end of the entire mix is clear from unwanted sounds so that the selected instruments (sub, bass, and kick) can occupy that region boldly and clearly. Suppose you want to be a dedicated mix engineer. In that case, you’ll take the time to apply specific EQ on every single channel in the mix, precisely cutting out the unnecessary low-end to establish a good starting point for clarity. 

Having a good understanding of frequencies is fundamental if you want to be a good mixer. This stems beyond what has been discussed in this article into the realms of knowing the good and bad characteristics of all of your sounds so that you can take it a step further than just cutting out the low-end and clear unwanted regions of every track along the way. All of the elements in the mix overlap, so it’s imperative to make sure that each one is contributing meaningfully and sounds good with everything else. 

Beware of making the common mistake of applying EQ on a track that’s in solo because unless you’re very familiar with frequencies and EQing, you won’t be sure that you’re making a positive impact on the rest of the mix. Train your ears to determine which sounds you’re affecting and hear the subtle effects that are being made – are they good or bad? You know that good is the only option. If it’s bad, don’t do it, or do it differently. 

Don’t be afraid to put multiple EQs after each other that are each set to affect different regions of the same things in order to have more control. Perhaps you might use a specific EQ that is clean and doesn’t add any character to the overall sound to cut and clear frequencies before you apply an EQ that adds character afterward. Remember, every EQ will affect the one after it in the chain so pay close attention to what it sounds like. 


As you get further towards a final product in the mixdown, you’ll start to use EQ in creative and different ways to help you achieve certain qualities or to affect entire groups and even the entire mix bus or master channel. However, the more you practice EQ and take the time to learn and understand, the better you’ll become at mixing because it is a fundamental element of it all. Stay tuned for some awesome plugins!


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