What expression pedals are compatible with GiO?

Apogee has tested the Yamaha FC-7 and the Roland EV-5.

First, the expression pedal’s 1/4” connector must be a 3-conductor TRS (tip-ring-sleeve) type. Pedals with a 2-conductor TS (tip-sleeve) are usually meant for analog volume control, and won’t work properly.

Even amongst 3-conductor expression pedals, there are two commonly used connection standards. Through the utility app GiOConfig, GiO supports both standards. Please see page 21 of the GiO User's Guide for details.