ALESIS DEQ230D - Manual (Page 53)

Basics of Equalization
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Constant Q vs. Variable Q
What makes the DEQ230 unique?
At their inception, graphic equalizers relied solely on a form of
equalization known as "Variable Q." The DEQ230, on the other
hand, is what is known as a "Constant Q" equalizer. This method
of equalization is a relatively recent development in the history of
sound reinforcement and recording technology. As you will see
illustrated in the charts in this section, the Constant Q method
allows for a higher degree of control over the sound being
processed because of its significantly greater accuracy.
Before we go any further, it's time for some definitions:
Q The range of frequencies affected by a
band
Variable Q A process in which the range of
frequencies affected by a band changes as the
amount of gain is cut/boosted
Constant Q A process in which the range of
Frequencies affected by a band stays the
same as the amount of gain is
cut/boosted
It may help to define these terms visually as well.
In the following illustration, we see the three basic terms that
govern the operation of a single band. The vertical bar of the
graph represents decibels of cut/boost, and the horizontal bar
represents frequency in Hz. The dotted line leading to the center
of the curve indicates the frequency at which this band is set. You
can see that in this example, Q covers a range of frequencies from
about 200 Hz to about 5 KHz.