The New Liturgical Movement website presents a story by Shawn Tribe that links to two historic recordings of chants lead by the members of the Solemes Abby who lead the revival of Gregorian Chant. These two did the research on the meanings of the neumes and their meanings; Dom Pothier in particular researched the cheironomic neumes that recorded the dynamics of a chant work. Both date back to 1904.
The first recording is the Choir of the Benedictines of San Anselmo reciting the introit to the Feast of the Assumption, Gaudeamus, with Dom Pothier directing.
The second is Dom André Mocquereau conducting the French seminary in Rome, who sing the Alleluia for Easter Sunday, Pascha Nostra Immolátus est Christus.