By John Moxey
Background
Use EQ to assist in the production of a quality recording, without changing the fundamental quality of the sound. This is good recording practice.
The term 'Equalization' or 'Equalisation', abbreviated as EQ, comes from the original intent of the invention - to make the recorded sound match the original source. EQ units are essentially a collection of frequency filters, often of different types, that provide the ability to reduce (attenuate) or boost (amplify) the signal strength of selected frequency bandwidths within a source signal. EQ is used to make up for inadequacies in the equipment and the recording environment, but it can also be used as a deliberate effect.
EQ types
There are various different EQ types:
Fixed Frequency
This is an Equalizer that operates at one or more specified frequencies, allowing the engineer to apply boost or cut at the specified frequency.
Graphic
This is an equalizer that operates on a number of fixed, preset frequencies. Any of these frequencies can be boosted or cut independently of the other frequencies. Graphic equalisers are normally composed of peaking type equalisers.
Paragraphic
This is a special type of Graphic Equaliser that allows the adjustment of the center frequency of each band to be adjusted by the engineer. Some also provide the ability to adjust the 'Q' or bandwidth of each filter.
Parametric
This is an equalizer that has a continuously variable center frequency, over a given frequency range. The 'Q' is also adjustable. If the 'Q' is not adjustable, the EQ is described as 'Sweepable', 'Tunable' or 'Quasi-parametric'.
Peaking
This kind of equalizer allows boost or cut to be applied to a source signal, using a bell shaped response curve. The Q setting determines the width of the bell while boost or cut determine the height or depth of the bell.
Shelving
This type of equalizer applieds boost or cut evenly to all frequencies beyond a threshold frequency using a shelf shaped response curve.
Sweepable
This kind of equalizer has a variable center frequency bu the 'Q' remains fixed.
Three Band
This kind of equalizer provides three separate frequency ranges that can be boosted or cut at the same time. Usually these are divided into low, mid, and high frequency ranges.
Two Band
This kind of equalizer provides two separate frequency ranges that can be boosted or cut at the same time. Usually these are assigned low and high frequency ranges.
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