Great Book of Organa

…the Magnus Liber Organi (“Great Book of Organum”) a collection of two-part organums for the entire church year. A generation later his successor, Pérotin, edited and revised the Magnus Liber, incorporating the rhythmic patterns already well known in secular music and adding more than one part to the cantus…

To him is attributed the Magnus liber organi (c. 1170; “Great Book of Organum”), a collection of two-voiced organum settings, notably of Gradual, Alleluia, and Responsory chants, for the complete liturgical year. (Organum is the elaboration of a plainchant melody by a countermelody sung above it.) In the Magnus liber,…

He also enlarged upon the Magnus liber organi, a collection of organa by his predecessor, Léonin, and made innovations in the use of rhythm. “Viderunt” and “Sederunt,” musical creations comparable in scope to the cathedrals of Gothic architecture, have both been recorded in modern performance.

…and, in fact, composed the Magnus liber organi (“Great Book of Organa”), which contains a series of two-part organa for the entire liturgical year. Pérotin, the apparent successor to Léonin, is cited for his three- and four-voice organa, as well as his “substitute clausulae,” newly composed clausulae intended for insertion…

Both men worked on the Magnus Liber Organi (“Great Book of Organum”), a collection of two-part organums for the entire church year.

…Léonin and Pérotin, wrote the Magnus Liber Organi, a compilation including settings of 59 Graduals and Alleluias in two to four voices. Some pieces have an unmeasured melismatic (many notes per syllable) upper voice over prolonged notes of the chant; others have measured, regular, recurring rhythmic patterns in all of…