The Pleni of Sanctus settings customarily uses a lighter texture, and does not rely on a cantus firmus. This Pleni is no exception. Obrecht here omits the tenor, resulting in a trio texture. An imitative duet between soprano and alto opens
the section. which is then followed by a duet between alto and bass. the contrast between high and low perhaps meant to suggest both heaven and earth full of His glory. The full trio texture is reserved for the conclusion of the section.
For more information, see:
Crocker, Richard L., and David Hiley. 2001 “Sanctus.” Grove Music Online. 30 Jul. 2018. www.oxfordmusiconline.com .
Hiley, David. Western Plainchant: a Handbook. Oxford: Oxford University Press, 1993. See in particular pp. 161-65.
Strohm, Reinhard. Music in Late Medieval Bruges. New York: Oxford University Press. 1985. See in particular pp. 146-48.
Wegman, Rob C. Born for the Muses: The Life and Masses of Jacob Obrecht. New York: Oxford University Press, 1994. See in particular pp. 169-74.