What is an equalizer?

David Mellor

David Mellor is CEO and Course Director of Audio Masterclass. David has designed courses in audio education and training since 1986 and is the publisher and principal writer of Record-Producer.com.

Saturday July 14, 2018
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An equalizer is used in pro audio to change the loudness balance of ranges of frequencies. For example, low frequencies can be made louder or quieter; high frequencies can be made louder or quieter; mid-range frequencies can be made louder or quieter. Equalizers are used in live sound, broadcasting, and in the recording studio.

An equalizer is used in pro audio to change the loudness balance of ranges of frequencies. For example, low frequencies can be made louder or quieter; high frequencies can be made louder or quieter; mid-range frequencies can be made louder or quieter. Equalizers are used in live sound, broadcasting, and in the recording studio.

There are several reasons for using an equalizer...

Types of equalizer

Equalizers may be either hardware units, or software plug-ins. They are available in several types...

Graphic equalizer

Klark Teknik DN360 2-channel graphic equalizer

Pictured above is a Klark Teknik DN360 2-channel graphic equalizer. Each channel has 30 slider controls, each covering a band of frequencies one-third of an octave wide. Each band can be cut or boosted by up to 12 decibels. The operator can shape the frequency curve to their requirements and correct any defects in the audio signal, or apply any enhancement that is considered necessary.

The positions of the sliders give a rough indication of the frequency response that is set. In the image, the frequency response is flat and there is no cut or boost at any frequency.

Parametric equalizer

Slate Digital SSL 4000E emulation

Pictured above is the Slate Digital plug-in emulation of the equalizer that features in each channel of an SSL 4000E mixing console. It features four bands of EQ - high-frequency, high-mid-frequency, low-mid-frequency, and low-frequency. There is also a filter which can be used to cut low frequencies.

The two mid-range bands are each parametric equalizers. A parametric equalizer has these controls...

Advanced plug-in equalizer

FabFilter Pro Q 2

Pictured above is an advanced plug-in equalizer, which is the FabFilter Pro-Q 2. It looks complex, and indeed it is very powerful, but you will see in the control section, lower center in the image, that there are controls for center frequency, gain, and Q, just as in the parametric equalizer above. The Pro-Q 2 offers up to 24 bands so that very precise control over frequency response can be achieved. There is also a display of the actual frequency response of the signal being equalized, so it is possible to see where problem areas might lie and then apply appropriate adjustment.

Examples of equalization

These examples of equalization offer a taste of what is possible. They are not intended to correct or improve the audio in any way but just to demonstrate equalization.

Firstly, the unequalized audio...

Low-frequency boost

Low-frequency cut

High-frequency boost

High-frequency cut

Mid-frequency boost

Mid-frequency cut

 

Summary

An audio equalizer is used to control bands of frequencies in vocals, instruments and complete mixed recordings, either to correct problems or provide subjective enhancement.

The music used in the examples is Wo Sind Sie by Audio Masterclass Featured Artists Monique Marissa Lukens and Jake Benson.

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