Mass 18
Mass 18 is the simplest Gregorian chant Mass. It is employed on weekdays in Advent and Lent.
Kyrie
This one is good, except they are alternating cantor and choir like at a Low Mass.
https://www.youtube.com/watch?v=0Yuz6GT45_Q
We will sing it more like this - join in on the bold words:
Kyrie eleison, Kyrie eleison, Kyrie eleison,
Christe eleison, Christe eleison, Christe eleison,
Kyrie eleison, Kyrie eleison, Kyrie, eleison.
Sanctus
https://www.youtube.com/watch?v=EuS6G4TQWLo
https://www.youtube.com/watch?v=mnOjJwF2Reo