puer natus est nobis

Yes, today is Christmas and so accordingly here is offered a very old Christmas song: the Introitus Puer natus est nobis. You can google it yourself, of course, but the first one here has the plainchant notation as found in the Liber usualis.

But this has organ accompaniment (which seems to be the way it's done these days...I spent several days at the Abbey of Gethsemani and they did all of their plainchant not only in English but with organ also. I guess it does help the pitch not to deviate...) so the following one may be the way you're more used to hearing it:

Also this selection is found on In Dulci Jubilo's record Salve Feste Dies, and it's worth checking out because of their approach to the rhythm (the rhythmic values in "Gregorian" chant are highly controversial: it's known that there were different rhythmic values but what's not known is what they were).

In terra pax, let's hope...