This is a high-end MXR phaser with a 6-stage phase circuit, and the width and depth of the sweep can be switched in 4 ways with the intensity. The circuit uses a photocoupler, and the fluctuation when the SPEED is increased produces a psychedelic sound reminiscent of the "Uni-Vibe". The mellow and creamy sound is unique to vintage machines. In the past, many professionals used to set the SPEED to zero and color the tone