1. Willi Apel. 1958. Gregorian Chant. Indiana University Press. https://books.google.cz/books?id=8PjxAAzSK8sC Willi Apel. 1958. Gregorian Chant. Indiana University Press. https://books.google.cz/books?id=8PjxAAzSK8sC
2. C.M. Atkinson . 2009. The Critical Nexus: Tone-System, Mode, and Notation in Early Medieval Music . Oxford University Press . https://books.google.cz/books?id=D37AsgEACAAJ C.M. Atkinson. 2009. The Critical Nexus: Tone-System, Mode, and Notation in Early Medieval Music. Oxford University Press. https://books.google.cz/books?id=D37AsgEACAAJ
3. Bas Cornelissen , Willem Zuidema , and John Ashley Burgoyne . 2020 . Mode Classification and Natural Units in Plainchant . Proceedings of the 21st ISMIR Conference (2020), 869–875. Bas Cornelissen, Willem Zuidema, and John Ashley Burgoyne. 2020. Mode Classification and Natural Units in Plainchant. Proceedings of the 21st ISMIR Conference (2020), 869–875.
4. Studying Large Plainchant Corpora Using chant21
5. P.M. Ferretti. 1934. Estetica gregoriana: ossia Trattato delle forme musicali del canto gregoriano. Number sv. 1 in Estetica gregoriana: ossia Trattato delle forme musicali del canto gregoriano. Pontificio istituto di musica sacra. https://books.google.cz/books?id=vOWCnQEACAAJ P.M. Ferretti. 1934. Estetica gregoriana: ossia Trattato delle forme musicali del canto gregoriano. Number sv. 1 in Estetica gregoriana: ossia Trattato delle forme musicali del canto gregoriano. Pontificio istituto di musica sacra. https://books.google.cz/books?id=vOWCnQEACAAJ