Phasing pedals were originally intended to emulate the sound of a spinning Leslie cabinet, though the actual sound is somewhat unique and not really to be confused with a Leslie simulation. With a phasing pedal, the signal is split in two and one of the signal paths is "shifted" out of phase with the other signal from 0 to 360 degrees (hence the technical name "phase shifter") throughout a broad frequency range. The shifting signal is eventually mixed with the original so the "whooshing" phase sound is the result. Phaser effects can be pretty subtle (such as Van Halen's usage of the MXR 90 on the first Van Halen album) or more pronounced (such as the introduction to Prince's "Purple Rain"). Along with chorus and flanger effects, are best used in moderation so the effect is more pronounced.