PITCH CONTROL

A variable speed pitch control (or vari-speed) is a control on an audio device such as a turntable, reel-to-reel, tape deck or  CD player that allows the operator to deviate from a standard speed (such as 33⅓, 45 or even 78 rpm on a turntable). The latter term "vari-speed" is more commonly used for tape decks, particularly in the UK. Analog pitch controls vary the voltage being used by the playback device; digital controls use digital signal processing to change the playback speed or pitch. A typical DJ deck allows the pitch to be increased or reduced by up to 8%, which is achieved by increasing or reducing the speed at which the platter rotates.
See more at Wikipedia.org...