Multiphonics, is playing Chords on the Trumpet by one person.
Multiphonics is the act of playing a triad by one's self on the Trumpet.
Try this: Play middle C (below the staff) on the trumpet. Simultaneously HUM a "G"
(second line). When both tones are "in tune" and their respective intensities are
in proper proportion, you will be able to hear an "E".