21/20

Interval information

Ratio	21/20
Factorization	2-2 × 3 × 5-1 × 7
Monzo	[-2 1 -1 1⟩
Size in cents	84.46719¢
Names	minor semitone, large septimal chroma
Color name	zg2, zogu 2nd
FJS name	[math]\displaystyle{ \text{m2}^{7}_{5} }[/math]
Special properties	superparticular, reduced
Tenney norm (log2 nd)	8.71425
Weil norm (log2 max(n, d))	8.78463
Wilson norm (sopfr(nd))	19
[sound info]
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21/20 is a small semitone of about 85 cents. It may be found in 7-limit just intonation as, for example, the difference between 8/7 and 6/5, or between 5/3 and 7/4.

Although called a chroma for its proximity (and conflation in systems like septimal meantone) with the major chroma 135/128, 21/20 is a diatonic semitone in both Helmholtz-Ellis notation and Functional Just System because it is 5120/5103 smaller than the Pythagorean minor second 256/243.

See also

• 40/21 – its octave complement
• 10/7 – its fifth complement
• List of superparticular intervals
• Gallery of just intervals
• Septisemi temperaments, where it is tempered out
• Wikipedia: Septimal chromatic semitone