Andrew Lawrence-King explains:
As in nearly all music of this period, the musical notation does not specify when or what the instruments should play, although the text has many detailed references to string instruments, drums and even hand-clapping. Since the actions described in the text correspond so closely to period accounts of the Feast of Fools celebration, we felt confident in following references to instruments equally literally.
All the music is notated in a single melodic line, so the instrumental accompaniments and interludes are entirely improvised, employing drones, ornamentations of the melody by the simultaneous playing of several variants at once in heterophony, and elaboration of the single melodic line into polyphony, with parallel fifths or fully independent parts.
We are taking the bold step of extending this well-accepted instrumental style to the vocal choruses, with the singers improvising polyphonic conductus settings according to the same principles, taking as a model the notated polyphony of the Parisian composers of the Notre Dame school.
Polyphony itself was also associated with the Feast of Fools, when the presence of visiting singers from all around the country was combined with a permissive attitude towards liturgical or musical antics.