Ockeghem Missa Cuiusvis toni
Biblioteca Apostolica Vaticana, Ms. Chigi C VIII 234, f. 9v-106r.
This mass has perhaps caused the most controversy of all Ockeghem’s masses. There have been repeated discussions about how many versions and how exactly the mass can be performed. I proved years ago that there are only two versions of the mass:
Consequently, these two versions are published here. In the version on E there are no problems at all and it was probably the original version.
There are slightly more problems in the version on G then in the one on E, but these are only selective and can be solved by a # rather than by B molle. If you sing the version on F, it immediately becomes clear that both a Bb and an Eb are required. In fact, you are singing the version on G. The Gloria and Sanctus were edited in the version on F in order to show that B and Eb are required throughout in this version.