What is a chorus effect? In a nutshell, chorus effects can make a single instrument sound like two instruments being played simultaneously. They add a rich, lush, shimmering quality to your sound.
Chorus stompboxes and effects multiprocessors with chorus sounds alter the original signal coming in from your guitar, bass, or other instrument by adding a second sound with a slight delay and subtle pitch differences. The effect is similar to the ringing, chiming sounds that 12-string guitars produce naturally due to their paired strings that differ slightly in pitch and time. On electric instruments such as guitars, chorus sounds like the same signal running through two amps with a very slight delay between them and an ever so subtle pitch difference. In fact, Pat Metheny creates his trademark chorus sound this way, using no actual chorus effect at all.
Chorus effects will fatten up the sound of a bass, rhythm guitar, or solo guitar. They can be used with distorted sounds but are a fantastic way to create full-sounding clean sounds as well. Used with a stereo amp rig, chorus adds spaciousness. Many acoustic guitar amps include a clean-sounding chorus effect adding depth and character to the amplified signal. Chorus pedals can be very helpful in fattening up the tone of acoustic-electric guitars whose piezo pickups tend to sound a little thin.