Three other problems encountered when preparing 12th Century notation, like that found in the extant manuscripts of the Play of Daniel, for contemporary performance are reconstructing instrumentation, registration, and harmony. None of these elements are commonly made explicit in the score, and must be selected from a range of possible options by either the editor of a performance edition, or by the creative team of a particular production. Often, both are the case, as a good edition will strive not to represent an urtext or a document of a single interpretation, but instead will be devised as a critical edition, presenting the original material as minimally adulterated as possible, and offering possible solutions as a starting point for further exploration of the text by future performers.
Notation of 12th Century France took the form of a staff with four (but sometimes as few as one), rather than today’s customary five, lines and a C-clef designating were Do was located. Numes - squares, diamonds, and other symbols - gave shape to the musical line and, like an abudiga, suggested vaguely some rhythmic proportion, though a better guide to this would be the speech rhythms of the underlying text. Instrumental music, like dances, were not notated, but learned by rote from one musician to another. There were no written meters, no bar lines, and no key signatures or accidentals. Do, or C, was also relative, differing from town to town dependent mostly on the organ in the local church.
So even locating C is context-dependent. The revivalist can either research what C was in a particular place at a particular time, provided such information survives. But it still has to be playable by the instruments at hand, which are tuned to a homogenized and somewhat arbitrary standard. Strings can be retuned, but winds and keyboards are another matter. Since instrumentation is free, however, the revivalist has discretion to choose what instruments, if any, are to be used for a production based on his or her desired sound-world for the production, hopefully taking into account any that may be mentioned in the text and what would have been available when the work was new. As for whether and where to double vocal lines or improvise their own, that has much to do with the competence of the musicians on hand. Introductions and interludes are nowhere implied in the score, but it’s reasonable to conclude they were part of a performance practice for the same reasons we have them today: to set the mood and prepare the singers with an excerpt from the melody, and to provide some variance and contrast in largely strophic music. In the 12th Century, there would have been no need to indicate specifics, as custom and tradition would make clear what the musicians did not improvise.
Which vocal lines were solo, and which were to be sung by a single character? There are places were that is obvious from a dramatic standpoint, but others less so. Would a prelude or hymn be sung by the choir together, split between different solos, given to a single singer personifying some allegorical concept, or even sung by the congregation? We have no idea. Here the revivalist gets to create themes for the production, since the only guide we have is their imagination. It’s possible that this was a choice year-by-year for our 12th Century counterparts, the same way your average contemporary church arranges its yearly passion play on the fly. Casting voices is similar: parts might be written higher or lower, but only within one octave. Octave equivalence and transfer were already understood phenomena by that time. So, soprano or tenor, alto or bass? Most often, the gender of the character is fairly clear, until you remember women did not perform in liturgical plays. Boys and falsettists could have sung some women’s roles, with tenors singing others a travestie. Likewise, male altos are just as valid choices for what may look at first glance like bass roles. Voices of undernourished, smaller western Europeans do seem to have been higher than ours now, with basses only really coming into fashion around the time refugees from the collapsing Byzantine empire began arriving, bringing with them their bass-heavy liturgical stylings. But just as with the contemporary church passion play, consistency was likely not the first priority in medieval Beauvais, either.
Lastly, there are harmonies to consider. Just because we are left with a single melodic line does not mean we are limited to that. Heterophony is a feature of many improvisatory musical traditions, wherein multiple musicians differently ornament a common melodic line. It is found in Iranian classical music, Dixieland, and it existed in medieval Europe. Simple polyphony was also common outside the advanced forms then being developed in Paris, in the form of overlapping organa. A line would be doubled at a perfect interval, for instance a fourth below or a fifth or octave above, or a combination of fifths and octaves stretching over a great range. Where would such an effect be appropriate? To create an eerie, magical aura to a climactic cadence? To characterize a person or situation as learned, as opposed to rustic? Because it sounds cool? All of the above? Since performance practice was so flexible, we can expect that any number of similar effects might have been used for any number of reasons, yet all corresponding to their specific meaning within the normative idiom of the day, one we can only perceive through dense mists of history. Thus, the revivalist must come up with their own lexicon of signifiers and gestures, and maintain an internal consistency therein, since we have only the most tenuous access to the period ear, with which we might hear the world of Beauvais as it was nearly a millennium ago.