How is the independence of the black channels achieved?

How is the independence of the black channels achieved?

Black 1 and black 2 are both referenced to the same master clock, which is split. Each black channel has a separate clock phase adjustment which feeds a separate signal generator. Blacks 3, 4, 5 and 6 are all from the same clock, which feeds a separate generator for each output. Each output has its own timing controls.