Busoni was a virtuoso pianist, and his works for piano are difficult to perform. His Piano Concerto, Op. 39 (1904) is one of the largest such works ever written. Performances generally last over seventy minutes, requiring great stamina from the soloist. The concerto is written for a large orchestra with a male voice choir that is hidden from the audience's view in the last movement. British pianist John Ogdon, one of the champions of the work, called it "the longest and grandest piano concerto of all".