The Walrus ARP 87 is one of my favorite delays. The program knob uses four algorithms to define the delay used: digital, analog, lo-fi, and slap back. The X knob changes what the algorithm will do depending on position. (The tap temp needs to be reset when the program knob changes position. The algorithm also changes when the program knob is changed. ) Using the tap tempo gives an infinite number of possibilities for this pedal. This pedal can give you warm and ambient; all the way to dark and spooky.