Terry

There are other ways. The harmonizer, whether vocal or instrumental, needs some context, for example, to determine when to use a minor third instead of a major third. Playing chords is one way, but there are others. Another method is for the harmonizer to just sound the notes you are playing (for vocal harmony). But an easy method is to specify a key signature for a song and let that determine the harmony. All three of these approaches are used in my VoicePrism and most Digitech vocalists.