The smaller of the two diatonic intervals which encompass 3 degrees of the of the diatonic scale. The minor-3rd is composed of 1 tone (i.e., whole-tone) and 1 diatonic semitone, and is one chromatic semitone smaller than the major-3rd. Here is one example:
minor-3rd
| |
C D E F G A B C
t s
M2 m2
minor-3rd = t + s = (t-s) + 2s
= M2 + m2 = +1 + 2(m2)
Thus, the minor-3rd contains 1 chromatic semitone and 2 diatonic semitones (or equivalently, 1 augmented-prime and 2 minor-2nds). In 12-edo, the minor-3rd encompasses 3 equal semitones. It is the characteristic interval of the minor chord, minor mode, and minor scale, thus giving its name to all of them.
Narrowing the minor-3rd by one more chromatic semitone results in the diminished-3rd.
An interval in the range of 300 cents (¢). Common minor thirds in Just Intonation are 6/5 (315¢), 19/16 (298¢) and the Pythagorean 32/27 (294¢).
This interval is also called the "trihemitone" and "augmented second" in certain contexts.
More precise values for the ratios in the Chalmers definition above are:
ratio ~cents 6/5 315.641287 ~= 315 5/8 19/16 297.5130161 ~= 297 1/2 32/27 294.1349974 ~= 294 1/7
The 7-limit ratio 7/6 is also known as the "subminor 3rd". It is ~266.8709056 (~= 266 7/8) cents. Another type of "subminor 3rd" is the 5-limit ratio 75/64, which is ~274.5824286 (~= 274 7/12) cents.
Successively closer small-integer rational approximations to the 12-edo minor-3rd are:
ratio ~cents 13/11 289.2097194 19/16 297.5130161 25/21 301.8465204 44/37 299.9739036, less than 1/38 cent narrower than 2(3/12)
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