So... should all machine learning for music be end-to-end? See what we found in the full paper:
Pitch Contours as a Mid-Level Representation for Music Informatics
R. M. Bittner, J. Salamon, J. J. Bosch, and J. P. Bello.
In AES Conference on Semantic Audio, Erlangen, Germany, Jun. 2017.
[PDF]