0 to 48
This setting controls how randomly the reverberation engine works. This makes the sound more natural, by changing the many delay taps in the algorithm.
The modulation engine is designed to help reduce the pitch-shifting/chorusing artifacts often present when delay times are modulated to avoid metallic ringing in an algorithmic reverb. This can be helpful when trying to avoid pitch-shifting artifacts, like those often found when using other reverb algorithms, with instruments like piano.