Wah block

First, have the Axe-Fx recognize the expression pedal: go to I/O > Ctrl, and assign External1 to the expression pedal (use the Learn mode by pressing Enter). Select a preset and insert a WAH block. Enter Edit and go to to the Freq parameter. The block under Freq indicates that this is a parameter that can be attached to a controller. Press Enter and under Source select EXTRN1. The pedal has now become a wah. Adjust the Wah settings to your liking.