Electro-Harmonix POG Polyphonic Octave Generator
"Use the Electro-Harmonix POG Polyphonic Octave Generator to add one or 2 octaves up, and one octave down and blend all of them together with straight-through signal. Works on chords. Want your guitar to sound like a 12-string? The POG can do it or even make it sound like an 18-string. Fader controls for input, dry output, sub octave, one octave, one octave detune, 2 octaves, 2 octaves detune, and low-pass filter."
