Electro-Harmonix's Frequency Analyzer XO is a guitar effect pedal that adds moving harmonies to the note or chords being played. Unlike other ring modulators, the Frequency Analyzer has controllable high-order filters that reduce cross-distortions and enhance the variations. The Fine control lets you set a single frequency that will then be both added and subtracted from the original note or chord. The pedal's blend control lets you mix the new notes with the original. This is a must-have esoteric pedal, especially for techno cats.