Mournful and passionate, and possibly one of the most recognisable pieces of classical music in the world. Samuel Barber's Agnus Dei is a choral arrangement of his own Adagio for Strings. It's performed here by the perfectly blended vocals of VOCES8, one of Britain’s leading a cappella groups. Mindful Mix at the Proms explores the universal, timeless themes of night, stillness and prayer through the lens of composers old and new. Take some time out and watch it now on BBC iPlayer. | BBC Arts