As far as I can tell the xfade affects the modulation of the delay. If you play around with the xfade , mod depth and rate while playing you should hear it. Start around 50ms and go up in 20ms increments to hear the changes. It's pretty cool when you dial in your preference. I don't know of any other fx unit that does this, samplers probably. Hail to Eventide engineers for giving us more than we expected.