Sub Arturo Plebs - Structural Analysis - Pan-isorhythm in The Upper Voices

Pan-isorhythm in The Upper Voices

Isorhythm is present in the composition not only in the tenor, but also in the upper voices. However, these have isorhythmic repetitions only within each of the three main structural parts defined by the tenor repetitions, not across them. Inside each tenor repetition, each of the upper voices also repeats the same rhythmic pattern (but with a new melody) in each of the three taleae. As is common with isorhythmic motets, the upper voices are generally paced much faster than the tenor, often moving in eighth notes or fourth notes (minims and semibreves in medieval notation) where the tenor moves in long notes filling whole bars. The text of each upper voice is distributed in such a way that each of the three main parts, despite their diminishing length in time, has the same amount of text to convey (i.e. two stanzas in the motetus, three in the triplum). Thus, text declamation becomes progressively much faster towards the end of the composition, resulting in an overall effect of structural accelerando.

The metric and rhythmic relations between the three voices are quite complex. The triplum moves in tempus imperfectum cum prolatione maiore (6/8 time) throughout, no matter what the current meter of the tenor is; this results in complex patterns of overlap and syncopation. The motetus is even more complex, as it shifts between meters multiple times. This is indicated in the notation by frequent use of colaration, the use of note heads filled in in red to indicate that their temporal value is shortened to two thirds their nominal value.