Editing Syntonic comma (section)

{{short description|Musical interval}}
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{{Redirect|Chromatic diesis|27/26|Comma (music)}}
{{multiple image
| direction = vertical
| header    = Syntonic comma (81:80) on C[[File:Syntonic comma on C.mid]]
| width     = 200
| image1    = Syntonic comma on C HE notation.png
| caption1  = Helmholtz-Ellis notation
| image2    = Syntonic comma on C.png
| caption2  = [[Ben Johnston notation|Ben Johnston's notation]]
}}
[[File:Just perfect fifth on D.png|thumb|right|Just perfect fifth on D[[File:Just perfect fifth on D.mid]] The perfect fifth above D (A+) is a syntonic comma higher than the (A{{sup|{{music|n}}}}) that is a [[just major sixth]] above C, assuming C and D are {{small|{{sfrac|9|8}}}} apart.<ref name=Fonville/>]]
[[File:Major second on C.svg|thumb|right|3-limit 9:8 [[major second|major tone]][[File:Major tone on C.mid]]]]
[[File:Minor tone on C.png|thumb|right|5-limit 10:9 [[major second|minor tone]][[File:Minor tone on C.mid]]]]

In [[music theory]], the '''syntonic comma''', also known as the '''[[chromatic]] diesis''', the '''Didymean comma''', the '''[[Ptolemy|Ptolemaic]] comma''', or the '''[[diatonic]] comma'''<ref name=Johnston/> is a small [[Comma (music)|comma]] type [[interval (music)|interval]] between two [[musical note]]s, equal to the frequency ratio {{small|{{sfrac|81|80}}}} (=&nbsp;1.0125) (around 21.51&nbsp;[[cent (music)|cent]]s). Two notes that differ by this interval would sound different from each other even to untrained ears,<ref name=BBC/> but would be close enough that they would be more likely interpreted as out-of-tune versions of the same note than as different notes. The comma is also referred to as a ''Didymean comma'' because it is the amount by which [[Didymus the Musician|Didymus]] corrected the [[Pythagorean interval|Pythagorean]] [[major third]] ({{small|{{sfrac|81|64}}}}, around 407.82&nbsp;cents)<ref name=Lloyd/> to a [[just intonation|just]] / [[harmonic series (music)|harmonicly]] consonant [[major third]] ({{small|{{sfrac|5|4}}}}, around 386.31&nbsp;cents).

The word "comma" came via Latin from Greek {{math|κόμμα}}, from earlier {{math|*κοπ-μα}} = "a thing cut off", or "a hair", as in "off by just a hair".