The FX50B and FX55B are very high gain preamplifiers that are overdriven to produce a distorting of the input signal and help sustain the notes longer. These effects simulate the characteristic distortion of a guitar amplifier turned up so high that it "clips" the signal, distorting it. The FX50B and the FX55B have an extra amount of gain boost in their upper ranges for a greater distortion effect. These pedals make the distortion sound aggressive at any amplifier loudness level and sustain your notes.