# 3rd-tone / third-tone / 1/3-tone

[Joe Monzo]
###### 1. Approximate interval

Used in a general sense, approximately 1/3 of a whole-tone. One of the most famous instances of the application of the idea of 1/3-tones in music-theory is in the calculation of the 'relaxed chromatic genus' of the ancient Greek theorist Aristoxenus.

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###### 2. One degree of 18-edo

Calculated as the 18th root of 2, or 2(1/18), an irrational proportion with the approximate ratio of 1 : 1.039259226032, and an interval size of exactly 66 2/3 cents.

It is the size of one degree, and thus the basic "step" size, in the 18-edo (or 18-tET) scale, also called the "third-tone scale" or system. Two of the most famous advocates of this system were Ferrucio Busoni, in his Sketch for a New Aesthetic of Music [1907], and Ivor Darreg, who refretted guitars to this system and wrote many pieces using it.

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###### 3. One degree of 19-edo

The term "third-tone" is also often used loosely to express one degree, and the basic "step" size, of 19-edo (or 19-tET), which is ratio 1 : ~1.037155044 = exactly 63 3/19 cents.

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[John Chalmers, Divisions of the Tetrachord]

Any musical interval in the neighborhood of 67 cents (¢). The 28/27 (63¢) is a typical [just] third tone.

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