Polyphonic ringtones can create multiple tones and/or notes simultaneously. This produces a more natural and realistic sound for melodies compared to very old phones that could only produce one note at a time.
Unlike real-music ringers, polyphonic ringtones only simulate music using a pre-defined set of tones and instrument sounds. They cannot reproduce vocals or exact music.
See: Real-Music Ringers
Polyphonic ringers often come in file formats such as "MID" or MIDI.
Most polyphonic ringers can simulate the sound of various real instruments, instead of just tones. Different phones support a different number of simultaneous instruments (chords) - anywhere from 4 to 72 or more.