The second-mode tract Qui habitat is an overwhelmingly anxious chant. In verses 5 and 6, Evil appears in four metaphoric disguises. The auctor (my definition for the composer/writer/performer of medieval liturgical chant) highlights these disguises by microtones on the one hand. On the other hand, he/she neutralises an ellipsis between the two consecutive verses by an ingeniously placed quilisma-microtone combination. Impressive.
In this analysis, I concentrate on quartertones as intertextual links between the verbal and the musical text. In such context, quartertones have a function similar to words as paratext, which have their musical equivalent in parapitches: quartertones that signal rhetorical relevance in the verbal text. In the 500+ cases I analysed in seven manuscripts written between about 1000 and 1250 from Cluny in the south to Utrecht in the North all words highlighted by quartertones fit into the rhetorical schema of affect, logic and loci. Imagine a ringing bell at the moment a rhetorically important word was sung.
You may find my analysis as presented at Leiden University on November 30, 2018 here. Have a look at the technical analysis from my thesis here.