How do the Expression and Footswitch jacks on VoiceLive 3 work?
You can attach an expression pedal to the Expression jack and a Switch3 to the Footswitch Jack, then assign actions to them via the Setup and Preset menus.
The Footswitch jack is GLOBAL and will remain constant throughout your presets. If you have a Switch3 attached, you will define which controls you want assigned to your switches.
The Expression jack is PER PRESET and can change depending on what you need the expression pedal to do. In one preset, it could control Harmony Volume, in the next it could control Guitar Pan. It's totally up to you!
Additionally, you CAN connect a second Expression pedal to the Footswitch jack, so long as its the same make/model as the one you have connected to the Expression jack. The second expression pedal, the one in the Footswitch jack, remains GLOBAL and can be assigned via the Setup menu.
With the above setup, one of your expression pedal functions will remain constant, while the other can change from preset to preset.