What is 3D superposition?

Three-degree superposition: do+do above three degrees mi, and +mi, do above three degrees sol? 0? 2mi？ 0? 2sol is a triad, which is a chord formed according to the relationship of three degrees. Because there is a certain tension between sounds, it is often used in multi-voice music, but it is not a three-degree overlapping chord. For example, the chords of impressionist music works are mostly fourth degree, and there are also many non-third degree chords in national music.