Hard to hear : The paragon of the diegetic or source-music soundtrack is surely Nashville (1975), Robert Altman’s densely woven tribute to the Mecca of country music which is also a dystopian meditation on the violence immanent in American politics. Set on the eve of the US bicentennial in 1976, Altman’s film is a complex pastiche of vignettes in which music plays a central narrative role, with…