Chorus Pedals

Chorus pedals mimic the effect choirs and string orchestras produce naturally, by having slight variations in timbre and pitch, by mixing sounds with slight differences in timbre and pitch. A chorus effect splits the instrument-to-amplifier audio signal, and adds a slight delay and frequency variations or "vibrato" to part of the signal while leaving the rest unaltered.  A well-known usage of chorus is the lead guitar in "Come As You Are" by Nirvana.