Fender's EXP-1 Expression Pedal is a dynamic dual-mode digital pedal that controls the volume or amp/effect parameters on Mustang III, IV and V amplifiers and on the Mustang Floor multi-effects unit. Switch between "Volume" and "Expression" modes by stepping on the toe end of the pedal. Red and green LEDs indicate the mode in use. In "Volume" mode-indicated by illumination of the green LED-EXP-1 controls the master volume or can be turned off. In "Expression" mode-indicated by illumination of the red LED-the EXP-1 controls most Mustang amp and effects parameters. Common among these, for example, are the frequency parameters of a wah effect and the rate/time parameters of modulation and delay effects. The EXP-1 pedal puts great tonal control at your feet and provides a great way to make your Mustang amp or multi-effects unit even more fun, more expressive and more versatile.