What is Equalization (EQ in Music Production)?

by ReverbLxnd in Mixing

This article introduces the concept of equalization in music production, and explains what EQs are, how they work and why we use them in audio processing

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In this article, I want to introduce equalization (EQ). We’ll look at what it is, and where you should EQ so get a good basic understanding of the concept.

This is introductory. That means we will only be introducing the concept, not delving deep into the how-tos and techniques of EQ.

Let’s dive into it.

What is Equalization (EQ)?

Everyone’s looked at a stereo system or digital music player and seen the controls for bass and treble. These are very basic equalization controls or what we usually call EQ.

The first thing we need to understand right off the bat is that all sound is vibration.

The speed of that vibration is called frequency.

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What is a Frequency?

Frequency is a similar concept to pitch. Sounds that vibrate at a lower frequency are lower in pitch, and sounds that vibrate at a higher frequency are higher in pitch.

Frequency is a function of air vibration.

When you pull a guitar string, for example, it vibrates and creates rapid air changes in air pressure, or what we call sound waves.

The number of sound waves per second the string is vibrating at is the frequency of the string. And we measure it in cycles per second or hertz (Hz).

The frequency is what determines the pitch we end up hearing.

The human hearing range is 20 Hz to 20 kHz 20,000 Hz, and it differs from one person to another depending on age, ear structure, and so on.

The science is a little soft on this but there is an argument that sounds we can’t hear can affect us.

There’s been evidence that low-frequency sounds at a high decibel level can make us sick. And a lot of modern recording equipment can record way higher than any human can hear.

Why are we talking about all these? 🤔


Equalization, or EQ, is the manipulation of frequencies to produce the desired effect in an audio signal. Typically, we equalize to enhance good sounding frequencies and to minimize bad sounding frequencies.

Even when one instrument is playing one note, there is more than one frequency being produced.

EQ lets us change the relative level between different parts of the frequency spectrum changing the balance between the fundamental frequency, the overtones, and the percussive elements.

Why do we use EQ when making or mixing music?

We use EQ to control the frequency spectrum of a piece of audio.

Controlling the frequency spectrum allows us to do a couple of very awesome things.

To sculpt the sound image

We don’t always want the full frequency range of every instrument in our mix. EQ helps us sculpt the sound image.

When some frequencies are out of proportion to others, our brain doesn’t like it.

We want to boost what is desired and cut what is not to make the track sound better or more natural.

To bring the best out of each instrument

With EQ, you can bring the best out of each instrument and make sure the instruments don’t clash and muddy up the entire mix.

We use EQ so that an instrument sounds better by itself or in the context of other instruments.

To add color and set the mood

We use EQ to add color to our music or set the right mood.

This is more towards the artistic side of EQ.

To get a better grasp of these ideas, let’s jump into the types of EQ.

Types of EQ

There are two main types of EQs–two main ways that we equalize.

#1 — Graphic EQ

Graphic EQ uses a set of frequencies, each with its level control.

The simplest example of this is your car stereo. It’s got bass, treble and mid (if you’re lucky). That’s low, high, and the mid-range.

What frequencies are at each of the points?

Who knows. That’s all you have and you can either turn it up or down.

EQ is one of the most basic sound processors. One that is available even in the simplest car systems.

When we create music, we use much more elaborate and precise EQ tools.

#2 — Smiley face EQ

Graphic EQ is where the term smiley face EQ comes from. One main reason we tend to end up with smiley face EQs is because ears are very very sensitive to mid-range.

The shape of our ear canal is the size of a 1kz tone – the middle of the mid-range of the frequency spectrum when it comes to human hearing.

We hear mid-range sounds much more quickly than very high or very low sounds. We hear them immediately and we think they’re harsh-sounding.

So a lot of times, we will scoop out that mid-range and accentuate the high end and low end to end up with a more pleasant-sounding smiley face EQ.

The other type of EQ is called a parametric EQ.

#3 — Parametric EQ

A parametric EQ is a variable multi-band EQ that allows you to adjust the frequency, level (boost and cut) and bandwidth.

It starts as more of a blank slate, instead of being given a set of frequency bands that we can either turn up or down.

Parametric EQ is a three-stage process:

You can first choose what frequency you want. You then boost or cut that frequency. After that, you can change the bandwidth – how the frequencies around that fundamental frequency react to a boost or cut.

As you might imagine, a very wide curvature adjustment on a parametric EQ is much more dramatic than very narrow curvature.

This is because if you are going to boost 4kz, for instance, and all these other little frequencies around it, much more of the audio signal will get boosted.

A wide curve boost (low Qs) is very useful when you want to make a track brighter overall.

And a boost with a wide curve (low Qs) sounds more natural than a narrow boost.

On the other hand, a narrow curve boost (high Qs) is very important when you want to only cut something annoying on an audio signal.

Say for instance you’re ringing out a vocal microphone and someone has a headset mic and there’s feedback at a certain frequency.

You want to get in there and pin-point that frequency and leave everything else intact.

Another common scenario is when there’s a ring on a stereo drum, and you don’t want to cut anything but the one little annoying frequency.

Those two scenarios are good candidates for very narrow Qs.

A lot of times, what I’ll do to find the offending frequency, boost it up with a very narrow Q, and then sweep the frequency spectrum until I find the annoying frequency and turn it down.

Parametric EQ filters

If you ever hear the term filter, that typically refers to one or two bands.

The term filter could be used to mean something other than high cut or low pass filters, but most of the time, that is what that term means.

A parametric EQ has three different types of filters or shapes that select the range of frequencies we are going to adjust up or down.

#1: High pass or low cut filter and low pass or high cut filter

These terms can get a little confusing.

A low pass is just another name for a high cut, and a high pass is another name for a low cut.

High cut or low cut filters cut all frequencies below the selected frequency at a slope.

If I put my low pass or high cut at 4 kHz, it’s everything above 4 kHz–it’s letting frequencies lower than 4 kHz pass through.

The same logic goes for a high pass or low cut.

It’s letting the highs pass through and cutting the lows.

If I have a high pass filter at 60 Hz, I’m cutting everything below 60 Hz.

Both low cuts and high cuts are great for getting rid of unwanted rumble or noise.

#2: Shelf

A shelf adjusts all frequencies above or below the selected frequency. It boosts or cuts a frequency and everything above it below it.

A shelf is either a high or a low shelf.

A low shelf boost at 80 Hz, for instance, will boost 80 Hz and everything below 80 Hz.

#3: Bell Curve

A peak or bell curve EQ filter selects a center frequency with other frequencies on either side of the selected frequency being adjusted as well.

Essentially, a parametric EQ is bell-shaped.

EQ Controls

Frequency (the center of it all)

On a parametric EQ, we have a frequency control, which selects our center of frequency.

Gain (how much boost or cut)

We have gain, which selects how much boost or cut. That’s how much we turn it up or down.

Bandwidth or Q (how many frequencies on either side)

And we have bandwidth or Q, which is how much frequency on either side is going to get adjusted with our boost or cut.

Q is some mathematical function.

You use a wider Q when boosting and a narrower Q when cutting.

In Conclusion

Of course, we have a lot more to talk about on EQ.

Understanding both frequency and equalization is critical for any audio processing, and this is just an introduction.

There’s so much more coming.

This is why you should drop your email in the subscription form below if you haven’t already.

In the meantime, if you want to learn more about equalization and mixing, feel free to jump back to the mixing blog.

If you have any questions feel free to navigate to the contact form. That should be somewhere on this blog.

That’s it for this article.


I've been a musician and brought in my stuff for mixing and mastering, I've been my own producer where I wrote, recorded, mixed and sold my own stuff. Now, I'm *mostly* an audio engineer, where I only record and mix for clients. I'm currently based in Berlin, Germany, where I operate ReverbLand out of. Got a question? DM me on Instagram or Twitter @reverblxnd everywhere, or shoot me an email [email protected]. I'd love to hear from you.

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