Shelf Equaliser

High and low shelf equalisers affect the high or low frequencies, respectively, raising  or lower the level of all frequencies in the corresponding band by the same amount. Consequently, the frequency response looks a bit like a shelf above or below the rest of the audio band. Sometimes also known as bass and treble tone controls. The transition to the shelf is 6dB/Octave, and the maximum boost or cut is usually of the order of 12-18dB. Some designs allow the corner frequency to be altered, either continuously or to switched positions, and often the region between the high adn low shelf can be manipulated by one or more bell-type EQ band(s).