Though A Ceremony of Carols has long been associated with boy choristers, Britten originally anticipated women’s voices. So it’s a treat to hear the female members of the Choir of Merton College, Oxford, superbly accompanied by harpist Cecily Beer, offering boyish-sounding heft with pure tone, mature insight and artistry. The other big work, A Boy Was Born, involves not only full choir but also the college’s girls’ choir, equally pure-toned and impressively disciplined.