EQ: How to Use an Equalizer?

The equalizer (or equalizer) is undoubtedly one of the most important effects for audio mixing, along with dynamic compression.

While the principle is quite simple to understand (after all, it’s just an effect that allows you to adjust the amount of bass, mids, and treble…), using and setting an EQ correctly is something much more complex.

This is particularly why beginners in mixing tend to rely on settings like “add +3 dB at 200 Hz for this or that instrument” that they can read on the Internet or elsewhere.

Unfortunately, this is the best way to achieve poor equalization.

And poor equalization means a mix that doesn’t sound “pro”.

That’s why I’ve written this comprehensive guide on equalization, starting from the very basics but also including a lot of comments and tips that will help you gain clarity on using equalizers during mixing.

Article summary:

• What is equalization?
• Understanding the spectrum and frequency ranges
• Basic equalizer settings
• Types of EQ filters
• How to set an EQ?

What is equalization?

First of all, I suggest taking the time to truly understand what equalization is and what it is used for.

A definition of equalization

Equalization is simply an effect that allows you to attenuate or amplify certain frequencies of an audio signal.

For example, with an equalizer (hardware or software), it is possible to increase the amount of bass in an audio track. Or, to completely eliminate high frequencies.

More concretely, if we look at what the frequency spectrum of a note played on a synthesizer looks like, we get something like this:

As you can see, there is a frequency peak at the note we played (200 Hz), which is what we call the fundamental — but also a number of other frequency peaks, which correspond to what we call harmonics.

It is mainly the harmonics that allow us to differentiate instruments from one another, as the harmonic content will affect the timbre of the instrument.

With an equalizer, we can simply manipulate the harmonic content of the signal, by amplifying or attenuating certain frequencies.

If we now look at the frequency spectrum of a cymbal hit, we notice that it is more like noise (there is no fundamental frequency and harmonics that stand out regularly) — however, the principle is the same: the signal has energy over a certain frequency range.

This means that with an equalizer, we can also affect the texture of the instrument.

More concretely, equalization allows us to control and adjust the timbre of any audio recording.

What is the purpose of equalization during mixing?

To use an equalizer correctly when mixing a track, it is important to first understand what can be done with it.

There are four possible uses for an EQ, which can be grouped into two categories:

• corrective equalization: “I correct a problem”;
• creative equalization: “I make my audio track more interesting”.

Use #1: Correcting a problem with an EQ

For me, the primary interest of equalization is to correct frequency problems that can be heard in a recording.

Indeed, in almost any recording, there are issues: electrical/electronic interference, resonances related to the acoustics of the room or the microphone, poor frequency balance because the microphone was poorly placed…

All of this can be corrected with an equalizer.

Then, there are what I would call “energy overflow”: depending on the recording, it is possible that certain frequency bands stand out too strongly. This is not necessarily a problem per se, but it is something that we will attenuate with an EQ during mixing.

However, be careful: the equalizer is not a magic tool. It cannot create what does not exist.

Similarly, not all problems will be easily correctable: if your recording is tinted by significant background noise affecting the entire frequency spectrum, it will be impossible to completely remove that noise.

Tip: make sure to get the best possible recordings before diving into mixing. Equalizing your tracks will be greatly facilitated…

Use #2: Highlighting the positive aspects of a track

Another use of equalizers is to highlight the elements we like in an audio recording.

For example, let’s say we want to equalize a kick drum track.

After listening to the track, we think it sounds pretty good, but the nice low frequencies that contain a large part of the instrument’s punch are not emphasized enough.

Well, with an EQ, we will amplify the corresponding frequencies to rebalance the frequency spectrum of the track based on what we want to achieve in the mix.

Use #3: Separating instruments in the mix

Mixing a track involves ensuring that all the tracks (instruments, vocals, samples…) are balanced in terms of frequencies.

The goal is, among other things, to make sure all instruments are audible at the right level.

Equalization, precisely, will help us maintain a good balance between the tracks of a piece by allowing us to separate the instruments in terms of frequencies.

Let me explain:

Imagine that two instruments are present (= have acoustic energy) on the same frequency band.

In this case, the sound will be muddled, chaotic, and it will be difficult to distinguish between the two instruments.

On the other hand, if we use an EQ to attenuate that frequency band on the first instrument, the second will, of course, stand out more easily.

During mixing, we will therefore constantly seek to sufficiently separate the audio tracks of a piece so that they are all audible — or at least to prevent them from adding up in a non-harmonious way on certain frequency bands.

Use #4: Generating special effects (SFX)

Finally, the fourth possible use of an EQ is for everything related to special effects or a bit creative.

We are on the border between production and mixing.

For example, we often hear evolving equalization filters over time to create impressions of rising or falling power.

Here is a very good example (starting at 0’13”):

In the same vein, we regularly hear tracks with telephone/megaphone type effects, which do use distortion but are primarily based on very narrow equalization curves.

Understanding the spectrum and frequency ranges

The theoretically audible frequency range for a human being is located between 20 Hz and 20000 Hz (or 20 kHz).

Of course, this will vary slightly depending on the person, particularly based on age.

That said, this frequency range is the reference on which most equalizers are based, as can be seen in the screenshot of Fabfilter Pro-Q 3, one of the most well-known EQ plugins:

Ideally, to be able to equalize a track, you need to be able to recognize a frequency range with sufficient precision.

For example, if you hear a particular resonance in your recording, you need to be able to roughly identify the concerned frequencies.

There are also tools to train your ears, which I highly recommend.

That said, accurately recognizing a frequency band requires real training. Thus, I propose a simplified view of the frequency spectrum, divided into 6 main bands:

Bass, Part 1 (< 50 Hz)

Sometimes mistakenly called “sub-bass,” this frequency band truly corresponds to the lowest sounds.

Typically, those that you will only hear with a subwoofer or a very good headset.

However, this part of the bass should not be neglected, especially in modern music (dance…) where mastering the energy of the kick is essential.

Bass, Part 2 (50 — 250 Hz)

In this second band of bass frequencies, you typically find the kick drum, the bass, the punch of the snare drum, or even part of the body of male vocal recordings.

Potentially, therefore, quite a few instruments will compete: so be careful to ensure that your mix does not become too muddy in this area, at the risk of losing definition and punch.

Low-Mids (250 — 700 Hz)

Properly equalizing the low-mids is essential for a good mix. I would even say: it is probably the area where I hear the most mistakes in home studio mixes.

Indeed, this frequency band tends to make mixes “muddy” as English speakers say (you will sometimes see the term muddy) or to have a cardboard box sound.

And since low-mids also concern important instruments like vocals, guitars, synths, and keyboards… it can quickly become complicated to manage.

Be particularly careful not to excessively boost this frequency range.

Mids (700 Hz — 2 kHz)

I find that mids are a bit easier to control — probably because it is a frequency band to which humans are naturally sensitive.

We find vocals, synths, guitar, but also a bit of the aggressiveness or punch of certain percussions (kick drum…).

High-Mids (2 — 6 kHz)

The high-mids is an area that requires careful attention when mixing a track, as the sounds it contains can quickly become aggressive or annoying if they are overly emphasized.

Especially for vocal or drum tracks (I particularly think of cymbals on overhead takes, but not only…).

Highs (6 — 20 kHz)

Finally, the highs allow you to give air to the tracks.

Sometimes, they are even felt more than heard, especially above 12 kHz.

This is where we find the high fizz of guitar amps, but especially the definition of vocals or acoustic instruments.

So be careful not to neglect this frequency band… 🙂

Basic Equalizer Settings

Of course, choosing the right type of EQ for the right task is important — but generally, all EQs have the same settings.

Indeed, we find each time:

• a certain number of bands;
• the choice of a frequency;
• the gain adjustment;
• the Q factor.

Let’s take a closer look at what this entails, using animations created with the EQ from Ableton Live:

The Number of Bands

Each plugin allows for a certain number of corrections: we then talk about a number of bands.

For example, in the screenshot below, you can see that 4 bands are activated and then deactivated, thus allowing for 4 different corrections to the signal:

Gain Adjustment

The gain adjustment of EQs is very easy to understand: it is simply the level of amplification or reduction of volume applied to the base signal over a given frequency band.

Gain is measured in decibels (dB).

If it is above 0 dB, we are amplifying certain frequencies, while if it is below 0 dB, we are attenuating those same frequencies.

Frequency Selection

Of course, it is also important to choose the frequency band that will be adjusted with an equalizer.

For this, we will always select a single frequency.

A reference frequency, in a way.

If we are on a bell filter, this frequency will correspond to the central frequency of the equalization curve.

If we are on a low-pass filter, for example, it will be the cutoff frequency.

(We will talk about these types of filters in a moment)

Q Factor

Finally, although it is not always displayed, the Q factor is a ratio that controls the bandwidth in the case of bell filters.

A high Q factor means that the bandwidth is very narrow: the correction will therefore be very localized on the selected frequency.

Conversely, a low Q factor will indicate a wide bandwidth: the correction applied will therefore be very broad relative to the selected frequency.

Note that the Q factor also affects shelf filters, particularly regarding the shape of the curve.

Types of EQ Filters

There are tons of VST equalization plugins, all more interesting than the others.

Some have many buttons and settings, while others are more minimalist.

However, fundamentally, the shapes of the equalization curves they offer always fall into three main categories:

• high-pass and low-pass filters
• shelf filters
• bell filters

High-Pass and Low-Pass Filters

First, there is the high-pass filter or high pass filter in English.

As you can see in the image below, it allows you to gradually cut the signal below a given frequency known as the “cutoff frequency.”

In other words, you select a frequency, and the frequencies below it are progressively attenuated.

There is also an inverse filter that allows filtering the highs: this is the low-pass filter or low pass filter:

These two equalization curves are quintessential signal cleaning curves, used to remove elements that we do not want to hear (be careful though to go easy with the low-pass filter).

A note in passing: depending on whether you choose a very steep or a very gradual slope, this type of EQ filter will be more or less noticeable in the mix. For a natural attenuation, keep gentle slope settings.

Shelf Filters

Next, we find the high shelf and low shelf filters, which can be grouped under the name of shelf filters.

The low shelf filter works as follows: starting from the selected cutoff frequency, we amplify or attenuate the signal up to a given level.

This “given level” simply corresponds to the gain setting that has been selected.

For example, if you have a high shelf filter of +6 dB at 3000 Hz, it means roughly that from 3000 Hz you will start applying amplification until you reach a plateau at +6 dB.

The diagram below helps to understand all of this:

Conversely, to apply the same type of treatment but on the lows, there is the low shelf filter which works in the same way but allows you to affect the frequencies below the selected cutoff frequency:

Typically, this kind of EQ curve is useful:

• for making broad corrections, but less drastic than with high-pass and low-pass filters;
• or for musically lifting certain frequency bands.

Bell Filters

Finally, there is what is called the bell filter or bell filter.

Undoubtedly the most well-known, or at least the most used by beginners.

Simply put, the bell filter allows you to amplify or cut the frequencies of a signal symmetrically around a given frequency:

Moreover, depending on the selected Q factor, the frequency band affected by the EQ filter will be more or less narrow around the chosen frequency.

This type of filter is ideal for making localized corrections or for broadly amplifying certain frequencies.

By the way, keep in mind the following guideline (which can be transgressed, by the way):

• when you attenuate frequencies, use a high Q factor;
• but when you amplify frequencies with a bell filter, use a low Q factor.

This will allow you to make the equalization more musical, less jarring in the mix.

How to Set an EQ?

Let’s say you are mixing a track.

You decide to equalize a track and you add your EQ plugin on it (paying attention to the order, especially in relation to compressors)

And now?

What to do?

Which setting to touch, and how to know what to equalize?

How to avoid the main equalization mistakes?

Certainly, online, you will often read “amplify this frequency or cut by 10 dB at 80 Hz”.

Problem: the equalization you will do depends solely on your recording and your mix. It is impossible to have a magic formula that allows you to equalize a specific instrument for sure.

However, do not forget that the golden rule of audio mixing is “If it sounds good, it is good!”.

Keeping this phrase in mind, and rather than giving you settings that you might not be able to use because they wouldn’t apply to your track, here is a simple method that will allow you to equalize any track.

Step 1: Clean the Track

In some recordings, you will find unnecessary noise that will pollute the audio spectrum at frequencies that do not correspond to the instrument you are trying to mix.

For example, it could be low rumblings coming from a guitar amp, or a hiss in the very high frequencies (>10 kHZ) if you are using a lot of distortion.

Generally, these unwanted noises that do not directly contribute to the sound tend to harm the mix because they will conflict with other instruments.

So use high-pass or low-pass filters to clean your track of these issues, but be careful not to overdo it: be careful not to distort your recording!

Note: However, note that if these audio parasites are not bothersome, you can skip this cleaning step, except of course in certain cases: typically, low frequencies are often filtered on the kick drum to achieve a more precise sound in the bass.

Step 2: Remove Problematic Frequencies

Once this little cleaning is done if necessary, you can focus on the rest of the sound.

Very often, and this is even more true for recordings made in a home studio context, your tracks will contain a number of problems or sounds that may seem unpleasant to you.

These may include:

• resonances at specific frequencies
• cardboard box-like sounds on percussion
• too “nasal” a sound on a vocal take
• etc.

You will therefore need to manage these problems, as once they are corrected, only the pleasant aspects of the recording will remain.

To make these corrections, the simplest way is to use the frequency sweeping technique:

1. First of all, identify the problem you want to correct: if you don’t hear a problem, there is no reason to equalize anything.
2. Take a bell filter on your favorite EQ, raise it to +10 or +12 dB with a narrow Q factor.
3. Sweep the frequency spectrum with this filter until the problem you identified stands out clearly.
4. Lower the gain setting of the bell filter to cut or attenuate the problematic frequencies, adjusting the Q factor as needed.

Note: No need to remove these frequencies too drastically, for example with a -40 dB filter. Often, a handful of decibels less is enough to make a problem less audible while preserving the musicality of the mix.

Step 3: Highlight Pleasant Elements

As I mentioned in the previous paragraph: once you have removed the majority of frequency problems from a track, in theory, only the sounds you want to hear remain.

However, you may sometimes want to go further and highlight certain aspects of the sound: more bass on a kick drum, more air on vocals, more mids on a guitar that is not present enough… the options are numerous.

To do this, you can use both bell filters to target specific frequency bands and low shelf and high shelf filters, which may be a bit more musical.

Try to keep boosts light to maintain the musical and natural side of the track: if you exceed 6 dB, it’s worth asking the question “is there another problem?”.

Note: Rules are meant to be broken. If, when you boost a frequency band to +12 dB, it sounds better than at +6 dB, then don’t hesitate to do it. Trust your ears…

And there you go!

And there you go, your track is equalized 🙂

You now have all the basics of equalization for mixing. Certainly, it is not the most complicated effect to understand, but it takes time to master.

However, to go further, I recommend reading my article on audio compression, which is just the second most used effect after EQ when mixing a track.