The book Octoechos is a liturgical book containing a repertoire of hymns ordered in eight parts according to eight echoi. Originally created in the Monastery of Stoudios during the 9th century as a hymnal complete with musical notation, it is still used in many rites of Eastern Christianity. The book with similar function in the Western Church is the tonary, and both contain the melodic models of an octoechos system; however, while the tonary serves simply for a modal classification, the octoechos is organized as a cycle of eight weeks of services. The word itself can also refer to the repertoire of hymns sung during the celebrations of the Sunday Office.
Papyrus fragment of a 6th-century tropologion found in Egypt, marked in red are the modal signature and some early ekphonetic signs of the following theotokion ("another one") which is composed in a melos of echos plagios devteros (D-Bk P. 21319)
Melkite Heirmologion, written in Syriac language, using Sertâ book script at Saint Catherine's Monastery, Mount Sinai (11th century) Oslo, Schøyen Collection, Ms. 577.
Georgian Iadgari (tropologion, 10th century)
The first printed Octoechos (Schweipolt Fiol, Kraków 1491)
Musical notation is any system used to visually represent auditorily perceived music, played with instruments or sung by the human voice through the use of symbols, including notation for durations of absence of sound such as rests. For this reason, the act of deciphering or reading a piece using musical notation, is known as "reading music".
A photograph of the original stone at Delphi containing the second of the two Delphic Hymns to Apollo. The music notation is the line of occasional symbols above the main, uninterrupted line of Greek lettering.
Music notation from an early 14th-century English Missal
Jeongganbo musical notation system