Fifteen complete Mass-settings by Mouton survive, of which Missa Tu es Petrus
is the only one not in four parts. Here a cantus firmus has four additional parts composed around it, making five in all. The cantus firmus is set unusually high in the texture. Indeed, in the Agnus Dei the tenor is notated with the rubric ‘in diatessaron’, meaning that it should be performed a fourth higher than written, thus creating a new and lighter texture for the final movement. Elsewhere the texture is varied by the omission of a voice part (usually the tenor, as in the Christe eleison and Crucifixus sections) or two (the Benedictus). Alongside his motets, the Mass as a whole demonstrates that, while aspects of his compositional technique are somewhat distinct from those of his great contemporary Josquin, Mouton is not just another sheep among the flock of Renaissance composers—he is, in the best sense, egregious.
from notes by Stephen Rice © 2012