Beginning on Maundy Thursday, there is a special antiphon for Psalm 51, which is sung quietly after each Canticle at Morning Prayer, Evening Prayer, and Compline during the Triduum. Each day, the length of the antiphon expands until it is at its fullest on Holy Saturday. Thanks to Sean Daenzer, we have the full antiphon sung as it is pointed on p. 448 of the Second Revised Edition of the Brotherhood Prayer Book. The rubrics on p. 445 explain the use of Psalm 51 during the prayer offices of the Triduum.
“Christ for our sakes became obedient unto death, even the death of the cross. Wherefore God also hath highly exalted Him, and given Him a Name which is above every name.”