Hodie Christus Natus Est (Christ is born today) is probably Jan Pietersoon Sweelinck’s best-known motet, if not composition of any kind. J.S. Bach was a great admirer of Sweelinck, and his music leads directly to the mature Baroque of the German master.
The sheet music is published by the TBQ Press - http://www.tbqpress.com/ Scroll down their listings to find the piece.
It is also available as an unpublished brass sextet.
The mp3 performance is from my CD “Savannah River Brassworks,” available on my Recordings page. We have rethought our tempo on this piece since recording it, and take it at the tempo on the pages.