Echos

Echos (Greek: ἦχος [ˈixos] "sound"; pl. echoi ἦχοι [ˈiçi], Old Church Slavonic: [glasŭ] "voice, sound") is the name in Byzantine music theory for a mode within the eight mode system (oktoechos), each of them ruling several melody types, and it is used in the melodic and rhythmic composition of Byzantine chant ("thesis of the melos"), differentiated according to the chant genre and according to the performance style ("method of the thesis"). It is akin to a Western medieval tonus, an Andalusian tab', an Arab naġam (since 1400 "maqam"), or a Persian parde (since 18th century dastgah).

The noun echos in Greek means "sound" in general. It acquired the specialized meaning of mode early on in the development of Byzantine music theory since the Octoechos reform in 692.

In general, the concept of echos denotes a certain octave species, its intervallic structure as well as a set of more or less explicitly formulated melodic rules and formulae that represent a certain category of melodies within the musical genre. As such, echos is the basis for composing or improvising new melodies that belong to it, as well as for properly performing existing pieces that have been written in it. These rules include the distinction of a hierarchy of degrees (tones, notes), where certain degrees figure as cadence notes (ἑστώτες) around which the melody will revolve prominently, or on which the melody will end most of the time. However, only very late stages of the theory (19th-20th century) actually provide systematic descriptions of echoi, while earlier stages use mostly diagrams, indirect descriptions and examples. Explicit detailed descriptions must still be provided based on extensive analysis, as is the case with modal phenomena in numerous other cultures.

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