Some works quietly become masterpieces: Morton Feldman’s intense, spare and evocative Rothko Chapel (written for the octagonal building in Houston that houses his paintings) was challenging when new; I sang in it at Dartington in the 1970s. Now it seems an utterly natural, hieratic procession of contrasted friezes in which not a note is out of place; like Rothko’s visions, it is sombre but uplifting. After this half-hour immersion, anything else might be an anti-climax, but the sequence that follows of Erik Satie piano pieces (Sarah Rothenberg) and John Cage choral fragments (Houston Chamber Choir) traces a hypnotic line of innovation. In a week of mourning, a moving hour of reflection.