How does an Audio Equalizer work? An In-depth Guide

Most people are intimidated by the faders in an audio mixer system. This is nothing but an equalizer to control different parts of the frequency spectrum in an audio track. The role of audio equalizers started with the hardware components.

Early mixers with equalizers that had knobs to turn for treble and bass. They developed to the point of having multiple knobs to turn for each band in a frequency spectrum.

This truly revolutionized the production studios in the early 1970s and lead to the development of mixer boards with multiple faders, controlling multiple bands of frequencies.

The switch from knobs to faders started right there. The development of such mixer boards became a game-changer in the quality of the songs produced. It also showed how much editing you can do in the post-production of a song.

Before the development of equalizers, the sounds recorded always depended on the pre-recording sessions. There was always pressure for engineers to record with absolute perfection as you can’t change much in the post-production.

This was completely thrown out by the development of mixers and gave the creative freedom for mixing engineers to do wonders with the audio tracks.

An audio equalizer works by controlling the frequency bands across a complete audio spectrum of an audio track. These frequency bands can be manipulated by filters to generate multiple modulations in the audio track.

Just knowing that the audio equalizer works around frequencies will not get you far. You have to take into account how it stacks up against other equalizers and what the internal elements of it are.

In this article, I will walk you through an in-depth analysis of what an equalizer is and how to get yourself around it. Let’s get started.

What is an equalizer? 

An equalizer is software or hardware equipment used to make minute alterations to massive changes in the frequency spectrum of an instrument.

Equalizers have made a huge difference in the lives of mixing engineers to make precise changes in the frequency spectrum.

Equalizers can work through the frequency spectrum and find the changes that are required from 20 Hz to 20 kHz.

Equalizers are used for a variety of purposes including cleaning up the low end of a high-pitched vocal and cleaning up the high end of a bass guitar.

The ability of an equalizer to make massive improvements in the quality of the track changed the music industry.

This gave advancements in the area of side chaining, which is a balancing technique used to adjust two instruments that share the same frequency range.

The ability of an equalizer is quite underrated. If you have a track where there are background noises in the low end of the spectrum, you can remove them easily and precisely without affecting the actual vocal performance recorded in the track.

This precise ability to make changes puts equalization as one of the important techniques to learn as a beginner music producer.

Equalizers are used mostly in shaping the vocal performances in a song. They play a major role in making the song sit properly with the instruments that are played in the background. Check out our article on how to equalize vocals here.

Vocals are an important part of music production. Even though the beat has more weight in the frequency spectrum, vocals are manipulated more with equalizers to make them sit correctly between the instruments.

Cleaning the low end of the vocals with an equalizer gives space for other instruments in the same spectrum to shine even more. Using filters from the equalizer adds dimension to the elements in a song.

Equalizers also allow the music producer to eliminate rumble in the low end, which is detrimental to the audio speaker and listeners.

Every vocal or instrument that you come across in the frequency spectrum of a song has a frequency range. When they exceed the range, they start to disturb the whole song. Interference and phase issues occur in the song, giving rise to distortion.

A standard male voice starts at 85Hz and extends up to around 6 kHz. On the other hand, a female voice starts at 300Hz and can extend up to 11 kHz.

When you look at the lower end frequencies, you would have to use different techniques for the male vocals as they have a lower end. This is the same for instruments as well.

As a music producer learning where each instrument should be in a frequency spectrum will make the process much simpler.

This is one of the reasons why experienced producers can make calculated changes to an instrument by just judging the song by ear.

Experience sets the value of a music producer rather than how many hits he has in the music industry. Equalization is one of the areas in music production where without any experience you would feel like you are a fish out of water.

Equalization is complex and takes years to master the frequency spectrums of each instrument.

Equalization, which started with faders and hardware equipment, has grown so much in the last 10 years. We have software equalizers that are capable of showing every intricate detail in a song.

Software equalizers offer a visual representation of the instrument that is being modulated. 

Hardware equalizer vs. digital equalizer 

Equalization first began with the hardware equipment. It slowly dominated the music recording studios in the 1970s and made its way into all hardware sound systems.

The hardware equipment also made its way into mixer boards by the end of the 1980s, causing a huge shift in the execution of mixing and mastering in the industry.

Today, hardware equalizers are still used in recording studios for live musical recordings and performances.

The advantage of using a hardware equalizer is that it offers the ability to adjust and manipulate a specific group of frequency bands rather than an individual frequency.

Hardware instruments add warmth and texture to the track which cannot be attained using a software instrument.

Hardware instruments are easy to handle when compared to software instruments as they have fewer options and functions to deal with.

When you look at all the available hardware equalizers, there are usually only three to four knobs. Generally, you would have a knob around 200 to 400Hz to control the low end.

The next knob would be for the mid frequencies around 800-1kHz and there should be another one for the higher frequencies from 11- 15 kHz. Some of the more advanced hardware comes with 6 to 7 knobs that control different bandwidths as well.

There is always a question about whether you should use a hardware or software equalizer and the answer is pretty simple when you look at what software equalizers offer.

Even though using hardware equalizer will offer warmth and more tonal harmonies, software equalizers make up for this in the manipulation abilities they offer.

Software equalizers were first brought into audio production software around 1998 and made a lot of progress in the 10 years that followed.

As software equalizers progressed more innovative functions and modulations were added.

These innovative modulations changed the way equalizers are used by producers in the studio and in audio production software.

The introduction of side chaining in the equalizer made all the difference in how the low end in songs was optimized.

The thumping effect of the bass that we hear in songs is produced with the help of side chaining with the equalizer.

The modulation, such as the filters which were introduced in the software equalizers, lead to advanced manipulation of instruments and vocals.

The ability to make a choir out of even a single vocal was made possible with such filters in audio production software.

Multiband equalization which was introduced in the software equalizers also makes a great difference in how the songs are manipulated in the audio production software.

This is a great change in the way equalization has been done throughout the years. The advantage of using a software equalizer as opposed to a hardware equalizer is justified here.

Before the introduction of software instruments and software equalizers, the hardware equalizers didn’t work well with the compressors at all.

They always had to use separate analog hardware to route the compression. This was eliminated with the introduction of software equalizers.

Software equalizers ensured that the compressors worked even inside the software. Even hybrid software equalizers with compression have been developed.

Multiband compression and equalization techniques were introduced to the industry as separate techniques used in both compression and equalization. Software companies brought them together.

Multiband compression along with equalization reduced the problems faced during the shift from analog to the digital software. The warmth that was missing in the software instruments was restored.

The compression along with equalization made way for more harmonization in the tracks as well.

How to use an equalizer? 

Understanding equalizers and the frequency spectrum takes time for any beginner, so it’s best to get your hands dirty and experience how the software works.

There are some guidelines that you can follow to make sure that you minimize errors when you are doing your first equalization project.

Let’s look at some tips about how you can get yourself started in equalization, without having too much of a hard time figuring things out.

When it comes to vocals, you should avoid making massive changes, and rather focus on the low-end roll-off. The audio visualizer in the equalizer will show you the frequencies of the particular vocal.

Simply put, roll off is cutting down everything below the starting point of the vocal. Some male vocals start at 110Hz and some female vocals start at 280Hz.

This completely depends on the person who is singing. When you start with a roll off then it’s important to find the sheen as well the high gain frequencies. You can learn more about how to equalize a vocal from our in-depth guide here.

When it comes to piano, things might get more complicated because the frequency spectrum spreads from one end to the other. This might be where people start to get intimidated.

The golden rule in equalization is to understand that you have to start with the trial and error approach.

Make a small change and see if it works out. If it doesn’t, revert back to the original and try again. Unlink other audio production techniques, the feel of the song solely depends on the tonic relevance.

Tonic relevance can be changed drastically in the equalization part of the production. If a producer were to cut the frequencies of a piano from 700 – 1400Hz, they would lose all the intricate details and the heavy mid-region ending up with just harmonies from the actual notes played.

This is one of the reasons why you have to pay careful attention to the changes you make and keep them minimal when using equalizers for the instrument.

For piano, start with rolling off the low end just like the vocals and boost the high frequencies by about 8 kHz to get the richness of the piano.

Strings are a completely different ball game in comparison to vocals and piano. This is just one of the reasons why it takes years for people to master how the equalizer works on each different element of the track.

For string instruments, when you boost a frequency too much, it results in harsh sounds in the middle thus either destroying the song or creating annoying hissing sounds.

When a string instrument is recorded including a guitar, the resonance and instrument taps are also recorded.

 If you boost a frequency that shouldn’t be boosted, it then causes an unpleasant sound. For strings, always roll off the low end and work your way around the mid frequencies to find out where too much resonance is showing up.

Whenever you find a resonance in the audio spectrum of the song uses a bell curve to push it down gently. This is called a subtractive approach, where you push the unnecessarily high frequencies down and in so doing, the important ones automatically shine through.

For drums, this is completely different as well. The lower end of drums is heavier than the higher end of drums in the frequency spectrum of any song.

Your goal when using an equalizer, should be in optimizing the lower end of the drums properly.

 Any additive or subtractive measure should be performed mostly in the lower end. Usually, the drum will have a high-end roll-off and a low-end boost.

This is opposite to other instruments and vocals. For bass, it is more similar to drums, where you would boost the lower end and roll off the higher end frequencies in an equalizer.

Why should you use graphic equalizers? 

Graphic equalizers have so many advantages when compared to software or hardware equalizers with just knobs on them. Graphic equalizers will help you to understand how the software works through the frequencies.

This is not possible with the analog software equalizers and hardware equalizers. When it comes to graphic equalizers, you can see visually which frequency you are boosting.

You will be more equipped to understand where the mistakes are on the particular track. The ability for any music producers to equalize properly is high when using a proper graphic equalizer.

The intuitive nature of the graphic equalizer will make the user more immersed in the experience of using it rather than being detached from it. This is not possible when it comes to other analog and analog-based software equalizers.

The immersion is something that will make you one with the instrument to understand the minute details of a song over time.

The ability to see what is going on in the song visually will help you to recall the experiences of audio equalization thus helping to gain more experience.

Multiband compression and equalization are better suited to be performed while you are using a graphic equalizer. When you are using bands of frequencies, you will not have any references in an analog equalizer.

When using a graphic equalizer, the ability to see which bands are being reduced and which are being boosted will help to analyze the compression being applied as well.

This is a step up from the previous generation of music production techniques because of software innovation.

Precision is another advantage that you will get from working with a graphic software equalizer which is not possible in analog equalizers.

The ability to nitpick which frequencies to boost and in some cases mark the frequencies with how much boost you need to apply, makes it easier to see the advantages in the software equalizer.

There are still producers who go for the analog equalizers because of the harmonization and warmth of sound. In a digital age where graphic equalizers are taking center stage, it will be really difficult for analog equalizers to make a comeback in the industry.

Filters in an equalizer 

Filters are the structural elements of an equalizer. They are helpful in additive and subtractive equalization in the track. Each filter is developed to make sure that they manipulate the targeted frequency without affecting the others.

This is the main difference between analog and digital equalizers. You get a lot more bang for your buck with a digital equalizer. Filters can also be stored as presets in a software based equalizer thus helping you in speeding up the process of mixing and mastering.

These presets can be assigned for a specific track or even a small portion of a frequency spectrum thus eliminating the hassle of having to replicate the process in the software.

If you have a particular artist that you record often, you can even save their preset and avoid going through the painstaking process of equalizing everything from start.

Let’s look at each one of the following filters

Low pass

A low pass filter is used to sweep frequencies from the right to left. It helps to clean up the high end of a frequency spectrum. The low pass can be used to clean up the high end that is not required for the track. This makes sure that the track is free from harsh high-end sounds that are not favorable to the track.

A low pass filter can also be called a high cut filter. It cuts the high end and moves from right to left. The low pass filter can be used for instruments that have too much white noise in the top end of the frequency spectrum.

When using a low pass, always make sure that the total gain in dB is lower than 6 to make minor adjustments. Anything higher will end up boosting the master volume, which might result in clipping.

High pass

A high pass filter is used to sweep frequencies from the left to right. It helps to clean up the low end of a frequency spectrum. The high pass filter can be used to clean up the low end that is not required for the track. This ensures that the track is free from bass heavy low-end sounds that are not needed on the track

A high pass filter can also be called a low cut filter. It cuts the low end and moves from left to right. The high pass filter can be used for instruments that have too much bass rumble in the bottom end of the frequency spectrum.

When using a high pass filter always make sure that the total gain in dB is lower than 6 to make minor adjustments or you will end up boosting the master volume. This may result in the song clipping.

Bell curve

Bell curve is completely different to both the high pass and low pass filters. In a bell curve, you have both the high pass and low pass filter, which means that in the middle you will get a high boost. Using this filter, you can ensure that either a particular frequency or a band of frequencies is boosted.

Bell curves are a great tool when working with complex instruments and when you are unsure about which frequencies to boost to make the track sound good. It helps to analyze the frequencies more effectively than a high pass or low pass filter on its own.

The bell curve also comes to the rescue when you are sweeping through the frequency spectrum to find resonant frequencies. These resonant frequencies are the culprits for harsh sounds that deteriorate the quality of the track.

Lowering the gain and making a steep bell curve will help you to navigate from one end to the other end to find these resonant frequencies. As you get better and better at finding the resonant frequencies, the quality of the songs will also improve.

When using a bell curve always make sure that the total gain dB is lower than 6 to make a minor adjustment to avoid boosting the master volume, which might result in clipping.

How do you set the equalizer to clear the sound?

Clearing the sound is about sweeping the sound from right to left or left to right. This is a technique used by a lot of music producers when they want to cut some sounds during a certain part of a song. This can be done with the help of a low pass or high pass filter.

Which equalizer setting is best for bass?

When you are setting your equalizer for bass always boost the frequencies around 110-180Hz and lower the frequencies around 400-600Hz. This allows having a balance in the mid-range and the low end where the bass is dominant.

Which is the best equalizer?

Digital equalizers which are on the market today are regarded as the best equalizers because they allow you to see the visual representation of all the frequencies in an audio spectrum. This gives more opportunities for the mixing engineer to make his changes and manipulation to be precise.

How do you equalize properly?

The basic rule for proper equalization is to have a reference track. Always compare the changes you have made. This method helps to train your ear for music mixing. 

Less is more is the most important principle in equalization as well.


Learning audio equalization takes consistent effort. There is no easy way to understand the process besides actually doing it yourself. It takes time to get your ears attune to identifying the errors and correcting them adequately.

Patience and the ability to concentrate to perfect each track is most important to make an audio equalizer work wonders in your project.

Making mistakes and learning from them to improve in equalization plays a great role in your progress as a mixing engineer or as a music producer.

Put in the time to learn more, you will succeed. In the meantime learn about how to equalize vocals here:

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