33edo

Prime factorization

3 × 11

Step size

36.3636¢

Fifth

19\33 (690.909¢)

Semitones (A1:m2)

1:4 (36.36¢ : 145.5¢)

Consistency limit

3

Distinct consistency limit

3

33 equal divisions of the octave (abbreviated 33edo or 33ed2), also called 33-tone equal temperament (33tet) or 33 equal temperament (33et) when viewed under a regular temperament perspective, is the tuning system that divides the octave into 33 equal parts of about 36.4 ¢ each. Each step represents a frequency ratio of 2^1/33, or the 33rd root of 2.

Theory

33edo is not especially good at representing all rational intervals in the 7-limit, but it does very well on the 7-limit 3*33 subgroup 2.27.15.21.11.13. On this subgroup it tunes things to the same tuning as 99edo, and as a subgroup patent val it tempers out the same commas. The 99 equal temperaments hemififths, amity, parakleismic, hemiwuerschmidt, ennealimmal and hendecatonic can be reduced to this subgroup and give various possibilities for MOS scales, etc. In particular, the terrain subgroup temperament can be tuned via the 5\33 generator. The full system of harmony provides the optimal patent val for slurpee temperament in the 5, 7, 11 and 13 limits.

While relatively uncommon, 33edo is actually quite an interesting system. As a multiple of 11edo, it approximates the 7th and 11th harmonics via orgone temperament (see 26edo). 33edo also tunes the 13th harmonic slightly flat, allowing it to approximate the 21st and 17th harmonics as well, having a 3L 7s with L=4 s=3. The 33c mapping (which has val ⟨33 52 76]) tempers out 81/80 and can be used to represent 1/2-comma meantone, a "flattone" (very flat meantone) tuning where the whole tone is 10/9 in size. Indeed, the perfect fifth is tuned about 11 cents flat, and two stacked fifths fall only 0.6 cents flat of 10/9. Leaving the scale be would result in the standard diatonic scale (5L 2s) having minor seconds of four steps and whole tones of five steps. This also results in common practice minor and major chords becoming more supraminor and submajor in character, making everything sound almost neutral in quality.

Instead of the flat 19\33 fifth you may use the sharp fifth of 20\33, over 25 cents sharp. Two of these lead to a 9/8 of 7\33, which is about 22/19 in size and may be counted as a small third. Between the flat 5\33 version of 9/8 and the sharp 7\33 version there is, of course, a 6\33 = 2\11 11edo interval of 218 cents. Now 6\33 + 5\33 = 11\33 = 1\3 of an octave, or 400 cents, the same major third as 12edo. Also, we have both a 327 minor third from 9\33 = 3\11, the same as the 22edo minor third, and a flatter 8\33 third of 291 cents, which if you like could also be called a flat 19th harmonic, but much more accurately a 13/11 sharp by 1.7 cents (if you use the patent val it is an extremely inaccurate 6/5). Another talent it has is that 7/5 is tuned quite accurately by 16\33, and we may put two 8\33 versions of 13/11 together to produce the cuthbert triad. The 8\33 generator, with MOS of size 5, 9 and 13, gives plenty of scope for these, as well as the 11, 13 and 19 harmonics (taking the generator as a 19/16) which are relatively well in tune.

33edo contains an accurate approximation of the Bohlen-Pierce scale with 4\33 near 1\13edt.

So while it might not be the most harmonically accurate temperament, it's structurally quite interesting, and it approximates the full 19-limit consort in it's way. You could even say it tunes the 23rd and 29th harmonics ten cents flat if you were so inclined; as well as getting within two cents of the 37th.

Other notable 33edo scales are diasem with L:m:s = 5:3:1 and 5L 4s with L:s = 5:2. This step ratio for 5L 4s is great for its semitone size of 72.7¢.

33 is also the number of years in the Iranian calendar's leap cycle, where leap year is inserted once every 4 or 5 years. This corresponds to the 1L 7s with the step ratio of 5:4.

Because the chromatic semitone in 33edo is 1 step, 33edo can be notated using only naturals, sharps, and flats. However, many key signatures will require double- and triple-sharps and flats, making notation very unwieldy in distant keys.

Harmonics

Approximation of odd harmonics in 33edo
Harmonic		3	5	7	9	11	13	15	17	19	21	23
Error	absolute (¢)	-11.0	+13.7	+13.0	+14.3	-5.9	-4.2	+2.6	+4.1	-6.6	+1.9	-10.1
Error	relative (%)	-30	+38	+36	+39	-16	-11	+7	+11	-18	+5	-28
Steps (reduced)		52 (19)	77 (11)	93 (27)	105 (6)	114 (15)	122 (23)	129 (30)	135 (3)	140 (8)	145 (13)	149 (17)

Intervals

#	Cents	Approximate ratios	Notation
0	0¢	1/1	Perfect Unison	P1	D
1	36.364	48/47	Augmented Unison	A1	D#
2	72.727	24/23	Double-aug 1sn	AA1	Dx
3	109.091	16/15	Diminished 2nd	d2	Ebb
4	145.455	12/11	Minor 2nd	m2	Eb
5	181.818	10/9	Major 2nd	M2	E
6	218.182	17/15	Augmented 2nd	A2	E#
7	254.545	15/13	Double-aug 2nd/Double-dim 3rd	AA2/dd3	Ex/Fbb
8	290.909	13/11	Diminished 3rd	d3	Fb
9	327.273	6/5	Minor 3rd	m3	F
10	363.636	11/9, 5/4	Major 3rd	M3	F#
11	400.000	5/4	Augmented 3rd	A3	Fx
12	436.364	9/7	Double-dim 4th	dd4	Gbb
13	472.727	21/16	Diminished 4th	d4	Gb
14	509.091	4/3	Perfect 4th	P4	G
15	545.455	11/8	Augmented 4th	A4	G#
16	581.818	7/5	Double-aug 4th	AA4	Gx
17	618.182	10/7	Double-dim 5th	dd5	Abb
18	654.545	16/11	Diminished 5th	d5	Ab
19	690.909	3/2	Perfect 5th	P5	A
20	727.273	32/21	Augmented 5th	A5	A#
21	763.636	14/9	Double-aug 5th	AA5	Ax
22	800.000	8/5	Double-dim 6th	d6	Bbb
23	836.364	13/8	Minor 6th	m6	Bb
24	872.727	5/3	Major 6th	M6	B
25	909.091	22/13	Augmented 6th	A6	B#
26	945.455	12/7	Double-aug 6th/Double-dim 7th	AA6/dd7	Bx/Cbb
27	981.818	30/17	Diminished 7th	d7	Cb
28	1018.182	9/5	Minor 7th	m7	C
29	1054.545	11/6	Major 7th	M7	C#
30	1090.909	15/8	Augmented 7th	A7	Cx
31	1127.273	23/12	Double-dim 8ve	dd8	Dbb
32	1163.636	47/24	Diminished 8ve	d8	Db
33	1200	2/1	Perfect Octave	P8	D

Nearby equal temperaments

Regular temperament properties

Rank-2 temperaments

Periods per 8ve	Generator (Reduced)	Cents (Reduced)	Associated Ratio (Reduced)	Temperament
1	2\33	72.727	21/20	Slurpee
1	4\33	145.455	12/11	Bohpier
1	7\33	254.545	8/7	Godzilla
1	8\33	290.909	25/21	Quasitemp
1	10\33	363.636	49/40	Interpental
1	14\33	509.091	4/3	Meantone/Dreamtone
1	16\33	581.818	7/5	Tritonic
3	2\33	72.727	3/2-1\3edo	Inflated
3	3\33	98.091	3/2-1\3edo	August
3	4\33	145.455	7/4-2\3edo	Triforce