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Septimal semicomma

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Septimal semicomma
126 / 125

13.79477 cents
2 · 32· 7  : 53

In music, the septimal semicomma, a seven-limit semicomma, is the ratio 126/125 and is equal to approximately 13.79 cents (About this sound play ).[citation needed] It is also called the small septimal comma[1] and the starling comma after its use in starling temperament.

Factored into primes it is:

Or as simple just intervals:

Thus it is the difference between three minor thirds of 6/5 plus a septimal minor third of 7/6 and an octave (2/1). This comma is important to certain tuning systems, such as septimal meantone temperament.

A diminished seventh chord consisting of three minor thirds and a subminor third making up an octave is possible in such systems. This characteristic feature of these tuning systems is known as the septimal semicomma diminished seventh chord.

In equal temperament[edit | edit source]

It is tempered out in 19 equal temperament and 31 equal temperament, but not in 22 equal temperament, 34 equal temperament, 41 equal temperament, or 53 equal temperament.

Sources[edit | edit source]

  1. Haluska, Jan (2003). The Mathematical Theory of Tone Systems, p.xxvi. ISBN 978-0-8247-4714-5.
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