The value that is being sorted isn't obvious to me. It's obvious that it is sorting it. I'm guessing maybe some dB level of each of the hits/notes. If that was the case, I'd expect the initial unsorted view to line up with the pattern of the waveforms which is not the case. Maybe it's just an unsorted list of values sorted in sync to the rhythm. It's weird though that the segment corresponds to a segment of the audio. I just don't see how they are linked.