The two sung prayers you can listen to here are Memento Domine David (Alleluia! Lord Remember David) and Inveni David servum meum (I have found David my servant).
They are modern recordings of pieces contained in a large, elegantly illustrated, choirbook in the V&A's collections. The choirbook was made around 1380, probably in Florence, for the Camaldolese Order. Choirbooks were usually large to allow several singers to follow the music at the same time. Music was, and still is, an important part of the Mass ceremonial. Choirbooks include numerous chants that would have been sung on the feast days of various saints. Gregorian chant was traditionally sung by choirs in convents and monasteries.
The music would originally have been performed by monks or nuns belonging to the Camaldolese Order. These two prayers were written between 750–770, hundreds of years before the choirbook was made, and are amongst the oldest used in the Mass. Normally two cantors (singers) would alternate with the larger choir.
These recordings were made by the Royal College of Music especially for the Medieval & Renaissance Galleries thanks to an award from the Arts and Humanities Research Council