"Miserere mei, Deus" is a motet written to be sung by two choirs. One choir is five voices - soprano, alto, two tenors and bass. The second choir has two sopranos, alto and baritone. One choir sings a simple kind of tune called a fauxbourdon which is based on a plainchant. The other sings a more complicated version, with a top part which goes up to top C (the note two octaves higher than Middle C). The singers also improvised some parts of the music, making up elaborate ornamented parts. These improvisations were not written down, but were passed from singer to singer in the choir.