Wolfgang Amadeus Mozart actually wrote his stylistically pace-setting Clarinet Quintet K. 581 for an instrument that has become known as the "basset clarinet," and which had four semitones more than the A clarinet in its lower register. The man who commissioned the piece, Mozart's friend the clarinet virtuoso Anton Stadler, had had this instrument made specifically for him, so that he was the only one able to perform the work at first. After Mozart's death, however, the work was soon published i...