orchestration requiem canticles is scored for contralto and bass soloists , mixed chorus , and an orchestra consisting of 3 flute ( 3rd doubles on piccolo ) , alto flute , 2 bassoon , 4 horn , 2 trumpet , 3 trombone , timpani ( 2 performers ) , 2 percussionists ( xylophone , vibraphone , and tubular bells ) , harp , piano , celesta , and strings .