The Parametric Equalizer
All parametric equalizers are variable.
The Q is another rotary control operating the same way as the sweep, but adjusting the bandwidth. The frequency range either side of the center frequency can be restricted or expanded to affect the desired part of the signal. Most types are 2/3 or 4 band units. The Q is measured in either Dbs/Octave (the gradient of the peak/dip) or in octaves (the total bandwidth affected).