Chorus effect takes the sound and duplicates it. It then plays back both sounds but the duplicate sound it slightly out of tune with the original. But the amount that it is out of tune varies over time. This is called Modulation. This effect can add fullness to the sound.
The Lexicon MPX550 24-Bit Dual Channel Processor has an award winning chorus included.
Some possible parameters of chorus software or hardware.
Rate: How fast the modulation happens.
Depth: The amount of modulation.
Predelay: How out of time the original is to the effected sound.
Feedback: Return of the effect sound back threw the chorus.
Effect Level: How much effect that is sent to the aux return bus.
Use Chorus sparingly as to much can ruin a good song.
Flange: Flange affects the sound in time not pitch.
Phase Shifting: Phase Shift affedts the sound in sound-wave position not pitch.