# Septimal semicomma

In music, the **septimal semicomma**, a seven-limit semicomma, is the ratio 126/125 and is equal to approximately 13.79 cents ( play ). 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

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

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