It is a superstructure. There are notes with the times of their events (MIDI note on, note off, polyphonic aftertouch, etc.) and editing operations that ultimat

It is a superstructure. There are notes with the times of their events (MIDI note on, note off, polyphonic aftertouch, etc.) and editing operations that ultimately alter those times; calculating the modified times from beat divisions, with beats beginning according to a current BPM rate, is an abstraction that introduces arbitrary entities for the convenience of the composer.