Bender Range Up/Down fields: Set the upward/downward pitch bend range.
Separate settings are available for upward and downward pitch bends—using your MIDI keyboard pitch bend controller.
When Bender Range Down is set to Linked, the Bender Range Up value is used for both (up and down) directions.
Note: Bending the string, just like the string on a real guitar, alters the shape of the modeled string, rather than acting as a simple pitch bend.
Download the guides:
Logic Pro User Guide: PDF
Logic Pro Effects: PDF