In this tutorial, you will learn what is an audio or music equalizer, how they operate, parameters, elements, types etc. Everything you need to know about audio equalizers.
So, what’s an Audio Equalizer?
An Equalizer is an audio processor which allows us to change the frequency content in an audio signal. Using an audio equalizer we can change a signal “boosting” or “cutting” decibels in particular frequencies. We normally use equalization when we want to modify the characteristics of our original audio signal, maybe for fixing mistakes during the recording stage, removing noise, or simply to change the tone and the “colour” of our sound according to our artistic criteria.
The Audible Frequency Spectrum
This concept corresponds with the frequency range at which humans can hear and it normally goes from 20Hz to 20.000.Hz. In order to section this range, there is a widely accepted subdivision of it.
Sub-Bass (20-60Hz)
You are more likely to ‘feel’ this sound more than hear it. These are really low frequencies, just a really big subwoofer can play them. Have you never been to a huge music festival and felt your body or chest vibrating? That was the Sub-Bass!. Not many musical instruments enter this frequency range, just some of them with a heavy bass component like a pipe organ.
Bass (60-200Hz)
In this range we can find the ‘body’, ‘fatness’ or ‘deepness’ of many instruments like the bass, double bass, cello, kick, piano etc. It is where fundamental notes of the rhythmic elements generally are.
Low-Mid (200-500Hz)
This is a very conflictive section. We can suffer from many troubles in our mix like the masking (when you can’t distinguish properly the different instruments). This is mainly due to the fact that many instruments have their main frequencies in this range (for example the human voice). It is also very common to have acoustics problems “room modes” within this range of frequencies since the wavelength of these frequencies corresponds with the normal size of a midsize room.
Middle (500-2000Hz)
In this area, we can find the vocal formants and therefore it is not a coincidence that our hearing is very sensitive to this range. We have to be careful when it comes to boosting this specific region since it can cause hearing fatigue.
Want to hear these frequencies? Check this video
Upper-Mid (2000-4000Hz)
Here is where many elements have their ‘punch’. We can also hear the ‘attack’ of the percussive elements. This area presents similar characteristics than the mid-frequency range, so we have to be careful if we don’t want to make an element so sound too ‘sharp’ or cause ear fatigue.
High end (4000 – 10.000Hz)
Also known as the ‘presence’ part of the spectrum. Manipulating this area we can create the illusion that the sound source is further (cutting) or close (busting). You should be cautious boosting these frequencies since it could make the mix sound too ‘harsh’. We can often find the harmonics of most of the instruments spread out around this spot.
Extreme High End (10.000 – 20.000Hz)
Around these frequencies, the signal usually decays and starts losing its strength. Its content is mainly harmonics and high-frequency noises. It is also called ‘the air’ or the ‘brilliance’ of the mixing because it gives us that sparkling or extra space feeling. This ‘air’ or ‘sparkling’ is usually desired in our mix but as with any other high-frequency sound, we have to be prudent with boosting.
Not all the human being have the same audible range. Usually, children have an optimal hearing and we start losing it as we grow. Hearing losing also depends about how caring we are with our ears agains loud noises, infections and different factors along our lives.
Elements of an Audio Music Equalizer
We are going to go through all the elements of a standard audio equalizer using as an example the plugin ‘Estudio EQ’ by Steinberg. This is the Cubase’s native eq plugin but… don’t worry! almost all the equalizers out there have the same parameters and work under the same logic.
As we can see along the horizontal axis the audible frequency range is displayed (20Hz-20KHz). On the vertical axis, we have the amount of gain or decibels we can ‘cut’ or ‘boost’ from a specific frequency (from -30 to +30Db).
Equalizers are formed with filters or ‘bands’ and there are several types. Our Studio EQ has 4 bands and the type of filter can be switched in all of them.
Types of EQ Filters
Low Pass Filter (LPF)
It attenuates the signal content above the cutoff frequency. We normally use them to remove high-frequency noise ‘hissing’ or the high content of an instrument. We can use a HPF to make our sound darker or pretend it is placed further or ‘in a box’.
High Pass Filters (HPF)
It removes or cuts the signal content below the cutoff frequency. HPFs are the most powerful tool when it comes to clean low-frequency noise or ‘humming’. It is quite common to apply HPF to most of the instruments which don’t have a very low-frequency content. Using this technique we can avoid masking problems and our mix will sound clearer in general.
Peak or Bell
Boost or cut the signal’s content around the selected frequency.
Notch Filter
it is mainly a Peak or Bell filter with a really narrow range of action. The most common use for notch filters is to remove resonances. Being drastic with notch filters can result in an artificial sound since it alters the original sign in a noticeable way.
Shelf Filter
Increase or cut the audio signal from the selected frequency to the end of the spectrum with a constant gain. It is quite common that tv or radio manufactures include this type of filters in their products’ music equalizer under the name of “bass” and “treble” (add or remove ‘lows’ or ‘highs’ from the signal).
Parameters of a Filter
- Frequency or cutoff frequency: with this parameter, we can control around which frequency our filter takes action.
- Gain: the number of decibels we want to attenuate or increase in the selected frequency
- Q Factor: this parameter can narrow or widen the affected area around the main frequency. A high Q factor will result in a very narrow filter (notch filter) and a low Q factor will result in a wider filter which affects more signal content. This parameter is more specific for music production purposes and it is normally a fixed value in the most common music equalizer we can find in many popular products.
Different Types of Audio Music Equalizers
Graphic Equalizer
It has all its bands or filters with a fixed frequency. They commonly have multiple sliders or faders to control the gain of each one of these filters. The more bands it has the more accuracy and versatility. However, we should not forget that this will mean a considerable rise in the price. They are more easy-to-use than the other types thanks to their visual support, and therefore, manufacturers include them in many products for the general public such as TVs, radios, hi-fi systems etc.
Parametric Equalizer
In this case, the equalizer counts with peak and shelf filters. It also allows us to use the 3 parameters (EQ, Frequency and Q Factor) in all of its filters. They are the most used equalizers inside the music studios due to their adaptability. Most of the EQ plugins are parametric.
Semi-Parametric Equalizer
They are practically identical to the parametric equalizers, except for the absence of the Q factor in their filters. You can not modify how ‘broad’ or ‘narrow’ are the action areas of each filter.
Active or Passive equalizers
We can also classify equalizers according to the nature of their components. When equalizers have active components they produce more harmonic distortion, emphasizing the odd harmonics (we could say they produce a more artificial and less ‘warm’ sound). They are generally cheaper, resistant and polyvalent, and that’s why we use them in all kinds of audio applications. On the other hand, we have passive equalizers, which are obviously made from passive components like resistances and coils. They are really expensive and fragile but in return of that, they barely generate any harmonic distortion and provide us with a warm cosy sound. You can find passive equalizers in top-notch mastering studios.
Equalization Charts
For audio beginners can be frustrating not to notice the subtle changes a music equalizer can make, or simply be overwhelmed by this amount of information. A good start could be this equalization charts which gives you an idea where the most common instruments have key eq areas. Remember that every sound and mix is different, so you shouldn’t take these frequencies as golden rules but as a starting point to play around.
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Alberto Echevarria
Founder of GoMixing.com
Graduated Audio Engineer by the University of Middlesex, London. Master in Recording and Music Production at the University of Stavanger, Norway. Mixing Engineer, Music Producer, Artist and Sound Designer.
