The Knee Trembler (Guy Pratt Signature Model) is an insanely good  tremolo effect with unique LFO, designed in direct collaboration with  Guy Pratt of Pink Floyd fame, perfect for his famous, “One of These  Days” bass intros, especially when coupled with the Echosex Baby. If you  miss the days when amps came with onboard tremolo, you’ll love the Knee  Trembler. It can be as smooth or as cutting of a tremolo as you would  want. And keeping in line with Foxgear’s devotion to excellence, it is  absolutely transparent and noise free.