Equalizer   

A device which changes the frequency characteristics of a signal. Unlike a filter, which attenuates portions of a signal's spectrum, equalizers permit passage of the whole spectrum with level changes to some frequency bands. If the energy in a certain band is raised it is a "boost" if it is attenuated then it is "cut".
 
equalization 
(types)
equalization 
(Level considerations, sound reinforcement)
equalization 
(boosting and cutting)