Trisagium
Someone asked about how to sing the Angelic Trisagion the official prayer of the Order of the Blessed Trinity.
The Trinitarian order doesn’t indicate any musical setting on their webpage but the pieces seem to be in the Divine Office.
The antiphon for the chaplet is taken from the Improperium or Popule Meus from Good Friday. Here’s a version where someone has taken just the Latin part
There is a responsory for the text “Tibi laus” in the Nocturnale Romanum, but it’s an elaborate thing from Matins with a different verse, so I psalm-toned it instead. That seems better suited to something repeated nine times.
There’s also a brief responsory starting “Tibi laus, tibi gloria” from the Antiphonale Monasticum
The “Te Deum” antiphon comes from the Magnificat Antiphon for Vespers of the Holy Trinity. Here it is on Gregobase
The last hurrah, “Libera nos,” is from the Nocturnale Romanum. Gregobase again
So, I’m not saying that this is the right way to sing it, but it is a fun way for people familiar with the Office and the Good Friday Liturgy.