Part of Digitech's double play pedals, this distortion allows you to program two channels of distortion and switch between the two or bypass them all together. There are seven knobs on this guy with a level and gain for each channel, a frequency selector (100hz-3.7khz) and cut/boost, and an octave control. One of the great pedals from the mid to late 80's--A Digitech PDS 1550 Programmable distortion (and delay). These pedals are set up not only to switch on and off, BUT also has 2 separately controllable distortions! Controls include Frequency, Octaves, Cut/Boost, Level A, Gain A, Level B and Gain B. Also, you can completely customize your sound by removing the bottom panel. Inside is a series of 7 DIP switches that controls 10, 20, or 40 ms of delay going to A channel, B Channel or both, Parametric to A channel or Both, Hi Filter controls, Low boost controls, and Delay on/off. Also has a trimpot inside to control Hi Filter cut/boost. There is a card inside the unit that explains these controls. Unit also has A & B Channel LED's.