I was first introduced to Gregorio Allegri’s ‘Miserere mei deus’ (the Italian composer’s setting of Psalm 51) by my mother whilst she was on a research sabbatical from teaching at Merton College, Oxford. I guess around 1995. Composed in the 1630s for exclusive use in the Sistine Chapel, it’s an extraordinarily beautiful piece of Renaissance church music. The story of how Mozart ‘stole’ the piece by learning it from heart and transcribing it afterwards is equally astonishing. Read more about it here.
Obviously, nothing beats hearing this live, in a church setting. But here’s one of the better YouTube settings I could find, by The Sixteen. And with the added bonus of the venue – St Luke’s in Old Street.