The current editions of Gregorian chant present the melodies written in black square-note notation on a four lined stave called a tetragram, and although there have been some typographical differences, this has been the case since the late Middle Ages in many places. This notation is called “diastematic”: it shows the exact height of pitches, though not certain rhythmic or phraseological aspects. 

Prior to these systems, there were others called “adiastematic”, which were indeterminate as to the pitch, but marked other aspects and served as an aide-memoire to the cantors for the melodies. The manuscripts are incredibly beautiful, but certainly very difficult to read for learning a melody.

One of these notation families is that of St Gall (named after the town in Switzerland where it was developed), which uses primarily two neumes, the virga and the tractulus. In this video, Vicente teaches us to interpret these neumes, as well as the function of the episema, by comparing the melody of the antiphon Dominus legifer noster, sung during the third week of Advent, in the St Gall adiastematic notation as found in Hartker's antiphonary, written at the end of the 10th century, and the same melody as it is notated in square notes in current editions.

The text of the antiphon is as follows:

Dominus legifer noster, Dominus Rex noster, ipse veniet, et salvabit nos 

"For the Lord is our judge, the Lord is our ruler, the Lord is our king; he will save us."

Learning to read both notation systems, which can be overlaid as they are in the Graduale Triplex, can be a wonderful tool in unlocking the correct interpretation of these chants.