A single timed event in a MusicStream: onset, duration, notes, and velocity.
Length in beats.
Notes sounding together; empty for a rest.
Onset, in beats of the stream's time signature (its denominator's note value) from the start.
Loudness, normally 0 to 1 (default 0.8).
A single timed event in a MusicStream: onset, duration, notes, and velocity.