8edo

← 7edo

8edo

9edo →

Prime factorization	23
Step size	150 ¢
Fifth	5\8 (750 ¢)
Semitones (A1:m2)	3:-1 (450 ¢ : -150 ¢)
Consistency limit	5
Distinct consistency limit	3

8 equal divisions of the octave (8edo) is the tuning system derived by dividing the octave into 8 equal steps of 150 cents each, or the eighth root of 2.

Theory

8edo forms an odd and even pitch set of two diminished seventh chords, which when used in combination yield dissonance. The system has been described as a "barbaric" harmonic system; even so, it does a good job representing the just intonation subgroups 2.11/3.13/5, with good intervals of 13/10 and an excellent version of 11/6.

Another way of looking at 8edo is to treat a chord of 0-1-2-3-4 degrees (0-150-300-450-600 cents) as approximating harmonics 10:11:12:13:14 (~0-165-316-454-583 cents), which is not too implausible if you can buy that 12edo is a 5-limit temperament. This interpretation would imply that 121/120, 144/143, 169/168, and hence also 36/35 and 66/65, are tempered out.

Notation

8edo can be notated as a subset of 24edo, using ups and downs. It can also be notated as a subset of 16edo, but this is a less intuitive notation.

Edostep	Cents	7mus (hex)	24edo subset notation		16edo subset notation
0	0¢	0	P1	D	P1	D
1	150	192 (C0)	~2	vE	M2	E
2	300	384 (180)	m3	F	M3	F#
3	450	576 (240)	^M3 / v4	^F# / vG	d3 / A4	Fb / G#
4	600	768 (300)	A4 / d5	G# / Ab	d4 / A5	Gb / A#
5	750	960 (3C0)	^5 / vm6	^A / vBb	d5 / A6	Ab / B#
6	900	1152 (480)	M6	B	m6	Bb
7	1050	1344 (540)	~7	^C	m7	C
8	1200	1536 (600)	P8	D	P8	D

This is a heptatonic notation generated by 5ths (5th meaning 3/2). Alternative notations include pentatonic 5th-generated, octatonic, and heptatonic 2nd-generated.

Pentatonic 5th-generated: D * E G * A C * D (generator = 5\8 = perfect 5thoid)

D - D#/Eb - E - G - G#/Ab - A - C - C#/Db - D

P1 - A1/ms3 - Ms3 - P4d - A4d/d5d - P5d - ms7 - Ms7/d8d - P8d (s = sub-, d = -oid)

pentatonic genchain of 5ths: ...Cb - Gb - Db - Ab - Eb - C - G - D - A - E - C# - G# - D# - A# - E#...

pentatonic genchain of 5ths: ...d8d - d5d - ms3 - ms7 - P4d - P1 - P5d - Ms3 - Ms7 - A4d - A1... (s = sub-, d = -oid)

Octatonic: A B C D E F G H A (every interval is a generator)

P1 - P2 - P3 - P4 - P5 - P6 - P7 - P8 - P9

Heptatonic 2nd-generated: D E F G * A B C D (generator = 1\8 = perfect 2nd = 150¢)

D - E - F - G - G#/Ab - A -B - C - D

P1 - P2 - m3 - M3/m4 - M4/m5 - M5/m6 - M6 - P7 - P8

genchain of 2nds: ...D# - E# - F# - G# - A - B - C - D - E - F - G - Ab - Bb - Cb - Db...

genchain of 2nds: ...A1 - A2 - M3 - M4 - M5 - M6 - P7 - P1 - P2 - m3 - m4 - m5 - m6 - d7 - d8...

Chord Names

Ups and downs can name any 8edo chord. Alterations are always enclosed in parentheses, additions never are. An up, down or mid immediately after the chord root affects the 3rd, 6th, 7th, and/or the 11th (every other note of a stacked-3rds chord 6-1-3-5-7-9-11-13).

8edo chords are very ambiguous, with many chord homonyms. Even the major and minor triads are homonyms. Chord components usually default to M2, M3, P4, P5, M6, m7, M9, P11 and M13. Thus D7 has a M3, P5 and m7. 8-edo chord names using 24edo subset names are greatly simplified by using different defaults: ~2, ^M3, v4, ^5, M6, ~7, ~9, v11 and M13. Thus D7 becomes ^M3, ^5 and ~7.

Chord edosteps	Chord notes	Full name	Abbreviated name	Homonyms
0 – 3 – 5	D ^F♯ ^A	D^(^5)	D	^F♯m or vGm
0 – 2 – 5	D F ^A	Dm(^5)	Dm	^A or vB♭
0 – 3 – 5 – 7	D ^F♯ ^A ^C	D^7(^5)	D7	^F♯m♯11 or vGm♯11
0 – 3 – 5 – 6	D ^F♯ ^A B	D6(^3,^5)	D6	Bm7 and vG,♯9
0 – 2 – 5 – 7	D F ^A ^C	Dm,~7(^5)	Dm7	F6 and vB♭,♯9
0 – 2 – 5 – 6	D F ^A B	Dm6(^5)	Dm6	Bm7(♭5)
0 – 2 – 4 – 7	D F A♭ ^C	Ddim,~7	Dm7(♭5)	Fm6

JI Intervals

8ed2-001.svg

Commas

8edo tempers out the following commas. This assumes val ⟨8 13 19 22 28 30].

Prime Limit	Ratio	Monzo	Cents	Color name	Name(s)
5	648/625	[3 4 -4⟩	62.57	Quadgu	Major diesis, diminished comma
5	250/243	[1 -5 3⟩	49.17	Triyo	Maximal diesis, porcupine comma
5	78732/78125	[2 9 -7⟩	13.40	Sepgu	Medium semicomma, sensipent comma
7	64/63	[6 -2 0 -1⟩	27.26	Ru	Septimal comma, Archytas' comma, Leipziger Komma
7	875/864	[-5 -3 3 1⟩	21.90	Zotriyo	Keema
7	(12 digits)	[-9 8 -4 2⟩	8.04	Labizogugu	Varunisma
7	6144/6125	[11 1 -3 -2⟩	5.36	Sarurutrigu	Porwell
11	100/99	[2 -2 2 0 -1⟩	17.40	Luyoyo	Ptolemisma
11	121/120	[-3 -1 -1 0 2⟩	14.37	Lologu	Biyatisma
11	176/175	[4 0 -2 -1 1⟩	9.86	Lorugugu	Valinorsma
11	65536/65219	[16 0 0 -2 -3⟩	8.39	Satrilu-aruru	Orgonisma
11	385/384	[-7 -1 1 1 1⟩	4.50	Lozoyo	Keenanisma
11	4000/3993	[5 -1 3 0 -3⟩	3.03	Triluyo	Wizardharry

Scala scale file

For those who use the new tuner Lingot, which accepts scala files, or for anyone else, here is a .scl file of 8edo 08-edo.scl

0. 1/1 C Unison

1. 150.000 cents C# (50 cents sharper than C# of 12-TET) Neutral 2nd

2. 300.000 cents D# Minor 3rd (identical to 12-TET)

3. 450.000 cents E Sub-4th, Supermajor 3rd (50 cents sharper than E of 12-TET)

4. 600.000 cents F# Tritone (identical to 12-TET)

5. 750.000 cents G Super 5th, Subminor 6th (50 cents sharper than G of 12-TET)

6. 900.000 cents A Major 6th (identical to 12-TET)

7. 1050.000 cents A# Neutral 7th (50 cents sharper than A# of 12-TET)

8. 2/1 C Octave

Pathological Modes

2 1 1 1 1 1 1 1L 6s MOS

Music

Tenacious Chorale (only movement II is in 8EDO) by Stephen Weigel

Fantasia in 8ET^{[dead link]} by Aaron Andrew Hunt

Fugue in 8ET^{[dead link]} by Aaron Andrew Hunt

Špendlíky play by Milan Guštar

Acoustic Improvisation in 8EDO^{[dead link]} by Ron Sword

Comets Over Flatland 7 by Randy Winchester

Malebolge by City of the Asleep

News To Me by Jake Sherman

Tomorrow Night (pop music from 2045) by Jake Sherman

FunkEight 1 by Carlo Serafini (blog entry)

8edo-pre-improv.ogg Preliminary noodling in 8EDO with ZynAddSubFX synth (by Cenobyte)

darkreflections(sketch).ogg 8EDO Ukulele (Cenobyte)

skiphop(sketch).ogg 8EDO Ukulele (Cenobyte)

octo-icy-pensive(sketch).ogg octo-icy-pensive-echo(sketch).ogg 2 versions of the same song, one with echo, one without. (Cenobyte)

Ear Training

8edo ear-training exercises by Alex Ness available here.

See also

• Octatonic scale - a scale based on alternating whole and half steps