The UT100 has three user-controllable parameters - Rate, Wave, and Depth.
Rate: This parameter controls the speed of the of the tremolo's volume sweep
Wave: This parameter controls the type of volume sweep. For example, setting this fully counter-clockwise will result in a sweep that fades in and out, whereas fully clockwise will give you the effect of a kill switch which either allows signal to pass through fully or not at all.
Depth: The parameter controls the how far the sweep will go. Fully counter-clockwise will result in a very small depth, with the signal seemingly affected by only a small amount. Fully clockwise will give a much larger depth which will result in the signal being affected quite heavily.
Experiment with different settings to get the result that sounds best to you.