The gap between two separated musical tetrachords is called the disjunction. In ancient Greek theory it was always the frequency ratio 9/8 (~203.9100017 cents). Below is a schematic diagram:
-- E
|
| D
tetrachord diezeugmenon
| C
|
-- B
tone of disjunction <
-- A
|
| G
tetrachord meson
| F
|
-- E
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