From Brett:
The Tap-A-Whirl V4 is the first true stereo pedal from the labs of Cusack Music, USA. It features 24 tremolo LFO types, brake up/down switching, expression control, 8 preset slots and the all-important Stereo Phase control which lets you offset the right channel for a zillion variations. It works fine in mono for simpler applications, but that stereo throb and movement - wow. Big sound.