The UN-16 is a delay and tuning phase effect that copies, delays, and detunes multiple voices, then spreads them about the stereo field. It sounds great with very little fussing.
With a mono signal going in and stereo outputs, the UN-16 will add stereo width to a mono sound. When stereo inputs/outputs are used, it can "thicken" a stereo sound with an effect similar to chorus.
To use the UN-16 to add stereo width to a mono source