The idea of improvisation, broadly defined, has been integral to our imagination of the medieval musical past. It can be related to many elements of production: to the act of un-notated creation; to the manipulation and amplification of notated materials; to our observance of rigid rules and formulae; or to spontaneous freedom. Likely a product of the Carolingian Renaissance, this is the first medieval music treatise to address an aspect of chant performance that does not only relate to a memorized repertoire, but includes an unwritten practice of extemporizing an accompanying voice to a pre-given melody. The art of “coloration” or the ornamentation of a line, whether polyphonic or monophonic, had been an integral part of extemporization si...