One of the reasons why I am attracted by piano performance is that there exist a moment when the left hand part’s notes and right hand part’s notes are weaving and entangled. In my theory, the relation between lower and upper part can be stated by a parameter, which can be expressed as ‘mutual distance’ or ‘independency’. It’s different from the completeness of chordal resonance. Sadly, I don't have an ability to describe what kind of unit this parameter is expressed by, but it’s certain that the state of two melodies’ mutual distance sometimes send a signal to our ears dramatically.
Though each part is played independently, the ‘mutual distance’ between them can be varied from ‘distant’ to ‘entangled’. A chorus of a piece, I think, had better be played in an entangled state. However, in many cases and at least for me, two parts seem to be played mutually distant, from a beginning to an end.
Luckily, we can enjoy an entangled state a little in this performance found on Youtube, on which two parts are weaving as shown in figure above.
