From the New Liturgical Movement

Coolest. Incipit. Ever!

By (Jeffrey Tucker)

Advent will soon be upon us, which means many things, among which is the annual fight--a polite one, no doubt--over who gets to sing the incipit (opening phrase) to the solemn version of Alma Redemptoris Mater.
Coming to York this Advent!

The Original Post on NLM has a splendid version of the solemn tone sung to Ambrosian Chant.