videos in AudioSet
A list of about a million ten-second YouTube clips, each labelled with the sounds in it, that Google published in 2017. Labs use it to train and test general audio and music models.
Including Wurdig Bist Du - You are Worthy - Byzantine Chant - 2nd Tone, Medieval Chant of the Templars - "Salve Regina", The Fall of Constantinople - Part II - 3rd Tone - Entire Chant is 11:52 minutes long.