Romeiko Ensemble performing a 17th century version of "Christ is Born" (Mode I) live at the Hellenic Library in Athens, Greece on December 13, 2006.
You can see this in high res video streaming at: http://www.liturgica.com/video/, as well as other hymns from this ground-breaking performance.
It should also be mentioned that the costumes worn for this performance were the same traditional costume worn by chanters in the Eastern Roman Empire prior to 1453.