Complex sentence: At his interview with the principal, Sir Alexander Mackenzie, he played Beethoven's "Appassionata" and two of his own early compositions--badly, he thought, but he was accepted and began his studies there in the spring of 1918.
Split into simpler sentences: At his interview with the principal, Sir Alexander Mackenzie, he played Beethoven's "Appassionata" and two of his own early compositions--badly, he thought. He was nonetheless accepted and began his studies there in the spring of 1918.