I spent a lot of my early teenage years in choirs, singing this kind of thing in the company of other, more musical boys. Actually spent a lot of time singing that particular thing again and again.
It's only 2 minutes long but it's 2 minutes of heaven, written by one of the great composers of the English Renaissance, William Byrd, sadly now largely forgotten.
Found it by mistake today. Downloaded to iTunes so I won't lose it again.
Beautiful. Spine-chilling. IMHO, anyway