21/20: Difference between revisions
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{{Wikipedia|Septimal chromatic semitone}} | {{Wikipedia|Septimal chromatic semitone}} | ||
'''21/20''' is a small semitone of about 85 cents. It may be found in [[7-limit]] [[just intonation]] as, for example, the difference between [[4/3]] and [[7/5]], [[8/7]] and [[6/5]], or [[5/3]] and [[7/4]]. | '''21/20''' is a small semitone of about 85 cents. It may be found in [[7-limit]] [[just intonation]] as, for example, the difference between [[4/3]] and [[7/5]], [[8/7]] and [[6/5]], or [[5/3]] and [[7/4]]. | ||
In what is known as an authentic cadence, there is a resolution from the V chord to the I chord. If the V is a [[4:5:6:7|harmonic seventh chord]], its harmonic seventh ([[21/16]] above the tonic) resolves down to the major third of the I chord ([[5/4]]) by a step of 21/20. | |||
== Terminology == | == Terminology == | ||
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== Approximation == | == Approximation == | ||
{{Interval edo approximation|21/20}} | |||
== Interval chain == | == Interval chain == | ||
An [[interval chain]] of 21/ | An [[interval chain]] of 21/20's stacked on top of one another comes close to approximating some important [[JI]] intervals. The error between the approximation and the target JI interval may be tempered out in some [[regular temperaments]]. | ||
Some examples include: | Some examples include: | ||
* A stack of two 21/20 upwards is ~ | * A stack of two 21/20's upwards is ~4{{c}} from [[11/10]]; | ||
* A stack of seven 21/20 upwards is ~ | * A stack of seven 21/20's upwards is ~9{{c}} from [[7/5]]; | ||
* A stack of ten 21/20 upwards is ~ | * A stack of ten 21/20's upwards is ~4{{c}} from [[13/8]]; | ||
* A stack of twelve 21/20 upwards is ~ | * A stack of twelve 21/20's upwards is ~4{{c}} from [[9/5]]; | ||
and | and | ||
* A stack of six 21/20 downwards is ~ | * A stack of six 21/20's downwards is ~10{{c}} from [[3/2]]; | ||
* A stack of nine 21/20 downwards is ~ | * A stack of nine 21/20's downwards is ~5{{c}} from [[9/7]]; | ||
* A stack of eleven 21/20 downwards is ~ | * A stack of eleven 21/20's downwards is ~4{{c}} from [[7/6]]. | ||
When treated as a scale, this interval chain can be called the '''[[ambitonal sequence]] of 21/20''' ('''AS21/20''' or '''1ed21/20'''). | When treated as a scale, this interval chain can be called the '''[[ambitonal sequence]] of 21/20''' ('''AS21/20''' or '''1ed21/20'''). | ||
1ed21/20 is equal to approximately 14. | 1ed21/20 is equal to approximately 14.2067edo, and as a result of tethering between compressed 14 and heavily stretched 15. It is quite [[xenharmonic]] in its sound. It is related to the [[nautilus]], [[sextilifourths]] and [[floral]] temperaments. | ||
1ed21/20 offers a possible approximation of the no-3s [[11-limit]], or alternatively of the 2.9.5.7.11.17 [[subgroup]]. | 1ed21/20 offers a possible approximation of the no-3s [[11-limit]], or alternatively of the 2.9.5.7.11.17 [[subgroup]]. | ||
{{Harmonics in equal|1|21|20|intervals=integer|columns=11}} | {{Harmonics in equal|1|21|20|intervals=integer|columns=11}} | ||
{{Harmonics in equal|1|21|20|intervals=integer|collapsed=1|start=12|columns=12}} | {{Harmonics in equal|1|21|20|intervals=integer|collapsed=1|start=12|columns=12}} | ||
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[[Category:Septisemi]] | [[Category:Septisemi]] | ||
[[Category:Commas named after their interval size]] | [[Category:Commas named after their interval size]] | ||
{{ | {{Todo|improve synopsis}} | ||