EX-P - Universal Expression Controller Pedal! Feel the need to express yourself fully M-Audio's EX-P expression controller pedal works with all M-Audio MIDI controllers that have an expression pedal input. A built-in polarity switch insures compatibility with most other brands of controllers and keyboards. Use the EX-P to control any assignable variable MIDI controller value including volume, modulation, panning, filter sweep and more. Durable molded construction with integral cable.