What is an equalizer?

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...

• A certain range of frequencies is too quiet. For example, low frequencies (bass frequencies) are too quiet and need to be boosted.
• A certain range of frequencies is too loud. For example, high frequencies (treble frequencies) are too loud and need to be boosted.
• A certain range of frequencies sounds unpleasant and needs to be made more mellow.
• A vocal or instrument sounds dull and needs to be made brighter.
• To help blend two or more vocals or instruments.
• To help blend a complete mix.

Types of equalizer

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

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

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...

• Center frequency (labeled kHz in the image), which is the frequency around which cut or boost will be performed.
• Gain (labeled dB in the image), which is the amount of cut or boost applied.
• Q, which sets the range of frequencies either side of the center frequency that will be affected.

Advanced plug-in equalizer

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.