According to Doctor Marage, who has studied Beethoven's letters, buzzing noises and other sounds started at around 1796. Deafness broke out in 1798 and Beethoven had lost 60% of his hearing by 1801. In 1816 he was completely deaf. By 1820, when he was almost totally unable to hear, Beethoven composed his greatest works. These include the last five piano sonatas, Missa solemnis, the Ninth Symphony, with its choral finale, and the last five string quartets.