Volume Faders (mixer channel order is 3-1-2-4 decks). When in THRU position, the crossfader will not affect the output level of the mixer channel. Select the L (Left) or R (Right) position to assign a deck to the left or right side of the crossfader. Use these switchers to assign each mixer channel to a side of the Crossfader. Blends audio between the channels assigned to the left and right side of the crossfader. Denon DJ - PRIME 4 - Layout MIXER CONTROLS