Expression pedal

Korg EXP2 Foot Controller for Midi Keyboard Versatile foot controller/expression pedal can be used with most Korg keyboards, modules and effect processors, when connected to the assignable pedal socket for normal use. It includes an adjustable minimum setting via the side mounted slide control and includes a 3-conductor cable.

https://www.korg.com/us/products/accessories/exp_2/