Over the last few years, theCastalian Quartet has won anumber of awards that testify to itsexcellence within a crowded field;its programme comprises Britten’s1945 masterpiece and a popularwork by a composer Brittenparticularly loved. Schubert’squartet refers to more than one ofhis songs, while its slow movementis a set of variations on a themefrom his incidental music to theplay Rosamunde.