When times are tough, how do you lure in audiences? “Two theories are doing the rounds. One says the only way to lure back the crowds is by going shamelessly populist. The other, unhelpfully, states the opposite: that you are most likely to prise open wallets when money is tight if you offer them something unusual, unrepeatable and unmissable. There can be no argument as to which camp the City of Birmingham Symphony Orchestra belongs in. In an amazing four-day festival in Birmingham from Thursday it offers (in conjunction with its sister ensemble, the Birmingham Contemporary Music Group) no fewer than 18 big, bold, bracing blasts of contemporary music, most of them composed in the past five years.”