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As I understand it, MIDI does not have the concept of an expression pedal – your Rocktron will treat the pedal as a MIDI controller device – you assign it a channel and CC number as part of the setup.

Because of the above, the Eclipse pedal calibration only works with actual foot pedals plugged into it (it can't know that a given MIDI controller is actually a pedal). So, it will be happy to respond to your Rocktron pedals, but you will have to use them as generic MIDI controllers.