“Symphony No 13, subtitled Hallucination City, was first performed in New York in 2001, and has been heard half a dozen times since then across the US and Europe. As with all the performances, the call goes out for recruits for the London show: 100 volunteers, all unpaid, must supply their own guitar and amp, be able to read music, and (to paraphrase) ought to have some idea what they’re getting themselves into.”