Tetracot

Tetracot, in this article, is the rank-2 regular temperament in the 2.3.5.11.13 subgroup generated by a "sub-major" second of about 174–178 ¢ which represents both 10/9 and 11/10. It is so named because the generator is a quarter of fifth: four such generators make a perfect fifth which approximates 3/2, which cannot occur in 12edo, resulting in 100/99, 144/143, and 243/242 being tempered out. This is in contrast to meantone, where 10/9 is tuned sharper than or equal to just in order to be equated with 9/8.

Tetracot has many extensions for the 7-, 11-, and 13-limit. See Tetracot extensions. Equal temperaments that support tetracot include 27, 34, and 41.

See Tetracot family or No-sevens subgroup temperaments#Tetracot for more technical data.

Interval chain

Tetracot is considered as a cluster temperament with seven clusters of notes in an octave. The chroma interval between adjacent notes in each cluster represents 40/39, 45/44, 55/54, 65/64, 66/65, 81/80, and 121/120 all at once. In the following table, odd harmonics and subharmonics 1–15 are in bold.

#	Cents*	Approximate Ratios
0	0.00	1/1
1	175.8	11/10, 10/9
2	350.6	11/9, 16/13
3	527.4	15/11
4	703.3	3/2
5	879.1	5/3
6	1054.9	11/6, 24/13
7	30.7	55/54, 45/44, 40/39
8	206.5	9/8
9	382.3	5/4
10	558.2	11/8, 18/13
11	734.0	20/13
12	909.8	22/13
13	1085.6	15/8
14	61.4	33/32, 27/26, 25/24
15	237.2	15/13

* In 2.3.5.11.13 subgroup CTE tuning

Scales

• Tetracot7 – 6L 1s scale
• Tetracot13 – improper 7L 6s
• Tetracot20 – improper 7L 13s

Tunings

Tuning spectrum

Edo Generator	Eigenmonzo (Unchanged-interval)*	Generator (¢)	Comments
	11/10	165.004
1\7		171.429	Lower bound of 2.3.5.11 subgroup 11-odd-limit, 2.3.5.11.13 subgroup 13- and 15-odd-limit diamond monotone
	11/9	173.704
	11/6	174.894
7\48		175.000
	11/8	175.132	2.3.5.11 subgroup 11-odd-limit minimax
	3/2	175.489
6\41		175.610
	13/11	175.899	2.3.5.11.13 subgroup 13- and 15-odd-limit minimax
	15/8	176.021
	5/4	176.257	5-odd-limit and 5-limit 9-odd-limit minimax
	13/9	176.338
5\34		176.471
	15/13	176.516
	5/3	176.872
	13/10	176.890
	13/12	176.905
4\27		177.778	Upper bound of 2.3.5.11.13 subgroup 13- and 15-odd-limit diamond monotone
	15/11	178.984
	13/8	179.736
3\20		180.000	Upper bound of 2.3.5.11 subgroup 11-odd-limit diamond monotone
	9/5	182.404

* Besides the octave

Music

Flora Canou

• "October Dieting Plan" from TOTMC Suite Vol. 1 (2023) – modus in 34edo tuning

Zhea Erose

• Modal Studies in Tetracot (2021) – in 34edo tuning

Xotla

• "Electrostat" from Lesser Groove (2020) – Spotify | Bandcamp | YouTube – ambient electro, tetracot[13] in 34edo tuning