The Sinfonia had an unusual entrance requirement, in that players had to either be non-musicians, or if a musician, play an instrument that was entirely new to them... The only rules were that everyone had to come for rehearsals and that people should try their best to get it right and not intentionally try to play badly... The early repertoire of the Sinfonia was drawn from standard classical repertoire so that most orchestra members had a rough idea of what the piece, or at least famous parts of it, should sound like; even if they could not play their chosen instrument accurately, they would at least have an idea that they should be going higher at one part then lower at another, and so on. The end result was the musical ensemble producing not only the correct note but several notes nearby, 'clouds of sound' that gave an average impression of the piece.
The group has not performed since 1979, but those who enjoy the video above can hear renditions of In the Hall of the Mountain King, The Hallelulah Chorus, The William Tell Overture, The Dance of the Sugar Plum Fairy, and other classic favorites at this YouTube link.