Complex sentence: A rare excursion from the opera house came in 1903 with Massenet's only piano concerto, on which he had begun work while still a student; it was performed by Louis Diémer at the Conservatoire, but made little impression compared with his operas.
Split into simpler sentences: A rare excursion from the opera house came in 1903 with Massenet's only piano concerto, on which he had begun work while still a student. The work was performed by Louis Diémer at the conservatoire, but made little impression compared with his operas.