Select either Channel 1, Channel 2 or Master to assign the selected FX bank (2 deck hardware) or Channel 1, 2, 3, 4 or Master Channel (4 deck hardware). Some hardware also has the option of assigning FX to an auxiliary channel (A).
When you assign a bank to Master any other channel assignments are removed, and selecting any channel while Master is selected will remove the Master channel assignment. You can turn off any channel assignment by clicking it again. You can assign both FX banks to one channel by selecting the same channel each bank.
NOTE: FX Unit 1 is assigned to Deck/Channel 1 and FX Unit 2 is assigned to Deck/Channel 2 by default when Serato DJ Pro is launched.