A while back I posted a link to a performance of Handel's Messiah in which the organist had a very bad day. Marc Geelhoed sends along a link on a similar theme — a page devoted to infamous trumpet bloopers. The Hummel concerto disaster and the Mahler Seventh catastrophe are not to be missed. As a bonus, there's an excerpt from the Portsmouth Symphonia's performance-recomposition of Also sprach Zarathustra. The Portsmouth was an avant-garde / comedic outfit founded by Gavin Bryars, featuring, among others, Brian Eno on clarinet. No one in the ensemble was particularly familiar with his or her instrument, which was the idea.
