Eco in The Name of the Rose describes near the end the monks singing Sederunt principes in organum, probably much like this example here.
“On the first syllable, a slow and solemn chorus began, dozens and dozens of voices, whose bass sound filled the naves and floated over our heads and yet seemed to rise from the heart of the earth. Nor did it break off, because as other voices began to weave, over that deep and continuing line, a series of vocalises and melismas, it—telluric—continued to dominate and did not cease for the whole time that it took a speaker to repeat twelve ‘Ave Maria’s in a slow and cadenced voice.And as if released from every fear by the confidence that the prolonged syllable, allegory of the duration of eternity, gave to those praying, the other voices (and especially the novices’) on that rock-solid base raised cusps, columns, pinnacles of liquescent and underscored numae. [Not sure they would still be in use, but I don’t know for certain.] …Until that Neptunian roiling of a single note seemed overcome, or at least convinced and enfolded, by the rejoicing hallelujahs of those who opposed it, and all dissolved on a majestic and perfect chord and on a resupine neuma.
“Once the ‘sederunt’ had been uttered with a kind of stubborn difficulty, the ‘principes’ rose in the air with grand and seaphic calm. …Now the choir was festively chanting the ‘Adiuva me,’ whose bright a swelled happily through the church, and even the u did not seem grim as that in ‘sederunt,’ but full of holy vigor.”
Particularly incisive on Eco’s part, I think, is how this music is so dynamically clever. The drama of the music is simply the word. How exciting the word “adiuva” can be, when elongated! The vowels themselves portray some sort of story arc. The phrase sederunt principes will go from loud (e) to soft (u) to brighter (i) back to loud (e) and, as he says, the second a will be quite the dramatic surprise in adiuva.