One-third octave


A one-third octave is a logarithmic unit of frequency ratio equal to either one third of an octave or one tenth of a decade. An alternative term for one tenth of a decade is a decidecade.
One octave is a factor of 2, so decades per octave, while a third would be.

Definitions

Base 2

18405:2017 defines a "one-third octave" as one third of an octave, corresponding to a frequency ratio of.
A one-third octave is precisely 400 cents.

Base 10

61260-1:2014 and ANSI S1.6-2016 define a "one-third octave" as one tenth of a decade, corresponding to a frequency ratio of . This unit is referred to by ISO 18405 as a "decidecade" or "one-third octave ".
One decidecade is equal to 100 savarts.