https://books.google.de/books?id=_SklDQAAQBAJ&printsec=frontcover&hl=de&source=gbs_vpt_read
The Advent Project: The Later Seventh-Century Creation of the Roman Mass Proper - James W. McKinnon...
"In this study in 'musical archeology,' James McKinnon reveals one of the most important layers in the early development of Gregorian chant. With equal...
the advent project