Of course the two pieces do not have everything in common. Each has its distinguishing
characteristics, each makes its own expressive gestures. And yet the similarities between the settings far
outweigh their differences, and quite deliberately so. Pairing like this served a purpose. The Gloria and
the Credo sampled in Ex. 9-12 enclosed between them a significant portion of the service: the synaxis,
given over to scriptural readings. The recurrence of familiar musical sounds to pace and punctuate the
service added an extra level of inspiring ceremonial to it. There is a Sanctus in the Apt manuscript—see
Ex. 9-13 for its incipit and opening phrase—that is even more similar in its melodic contents to certain
portions of the Ivrea Credo than the Ivrea Gloria. It might well have been modeled on the Credo, to secure
an additional return to familiar sounds that would thus inspiritingly organize even more of the service,
encompassing the beginning of the Eucharist as well. Basing one polyphonic piece on another like this
was called parody, from the Greek for “alter the song.” It did not at this point have any connotation of
satire.
EX. 9-13 Incipit and beginning of A siglum. Apt 27 (Sanctus)