Octave complement: Difference between revisions
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The '''octave complement''' or '''inverse interval''' of an [[interval]] is its interval distance from the [[octave]]. | {{Wikipedia|Inversion (music) #Intervals}} | ||
The '''octave complement''' or '''inverse interval''' of an [[interval]] is its interval distance from the [[octave]]. It can be seen as a binary symmetric relation over intervals. The concept is important in musical practice and most musical theories. Its use is typically restricted to [[octave-reduced]] intervals (including the octave). | |||
== Calculation == | == Calculation == | ||
Depending on the interval representation (name, ratio, monzo, edo steps, | Depending on the interval representation (name, [[ratio]], [[monzo]], [[edo]] steps, [[cent]]s), it's more or less easy to retrieve the complementary interval from a given interval. | ||
=== Classical interval names === | === Classical interval names === | ||
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=== Monzo === | === Monzo === | ||
Intervals represented as | Intervals represented as monzos can be transformed into their octave complement by inverting all arguments and increasing the 2-argument. | ||
; Examples | ; Examples | ||
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=== Edo steps === | === Edo steps === | ||
Octave-complement intervals represented as ''s\n'' meaning ''s'' steps of ''n''-EDO follow this relation <code>s1 + s2 = n</code>. For given s and n, the unknown x can be calculated by the formula <code>x := n-s</code>. | Octave-complement intervals represented as ''s''\''n'' meaning ''s'' steps of ''n''-EDO follow this relation <code>s1 + s2 = n</code>. For given ''s'' and ''n'', the unknown ''x'' can be calculated by the formula <code>x := n -s</code>. | ||
; Examples | ; Examples | ||
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=== Cents === | === Cents === | ||
Octave-complement intervals represented as ''s | Octave-complement intervals represented as ''s''¢ follow this relation <code>s1 + s2 = 1200</code>. For given s, the unknown x can be calculated by the formula <code>x := 1200 - s</code>. | ||
; Examples | ; Examples | ||
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* [[Fourth complement]] -- the analogue for the [[4/3|fourth (4/3)]] | * [[Fourth complement]] -- the analogue for the [[4/3|fourth (4/3)]] | ||
* [[Tritave complement]] -- the analogue for the [[tritave|tritave (3/1)]] | * [[Tritave complement]] -- the analogue for the [[tritave|tritave (3/1)]] | ||
[[Category:Terms]] | [[Category:Terms]] | ||
Revision as of 01:13, 2 September 2021
The octave complement or inverse interval of an interval is its interval distance from the octave. It can be seen as a binary symmetric relation over intervals. The concept is important in musical practice and most musical theories. Its use is typically restricted to octave-reduced intervals (including the octave).
Calculation
Depending on the interval representation (name, ratio, monzo, edo steps, cents), it's more or less easy to retrieve the complementary interval from a given interval.
Classical interval names
The intervals in western music have names derived from numerals, starting at 1 (unison or prime, second, etc.). These names are prefixed with further size attributes (just, minor, major, etc.) which express relative size relations (the attribute just is often omitted for unison and octave). Complementary intervals are calculated by complementing both, name and attribute parts. For the name part the complement is calculated by subtracting the ordinal number from 9, the attribute part is negated, just is the negation of just . The following tables show names with ordinal numbers (#) and attributes with size hints (~).
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- Examples
- minor third vs. major sixth
- (just) unison vs. (just) octave
- just fifth vs. just fourth
Ratio
Octave-complement intervals represented as ratios r follow the relation r1*r2 = 2. For given r the unknown x can be calculated by the formula x := 2/r or (for the ratio representation r = a/b) into x := 2*b/a (the result sometimes has to be reduced by the factor 2).
- Examples
- 5/4 vs. 2*4/5 = 8/5
- 4/3 vs. 2*3/4 = 6/4 = 3/2
Monzo
Intervals represented as monzos can be transformed into their octave complement by inverting all arguments and increasing the 2-argument.
- Examples
- [-1 1⟩ vs. [-(-1)+1 -(1)⟩ = [+2 -1⟩
- [3 -3 1⟩ vs. [-(3)+1 -(-3) -(1)⟩ = [-2 3 -1⟩
- [-2 2 1 0 -1⟩ vs. [-(-2)+1 -(2) -(1) -(0) -(-1)⟩ = [+3 -2 -1 0 +1⟩
Edo steps
Octave-complement intervals represented as s\n meaning s steps of n-EDO follow this relation s1 + s2 = n. For given s and n, the unknown x can be calculated by the formula x := n -s.
- Examples
- 7\12 vs. (12-7)\12 = 5\12
- 1\7 vs. (7-1)\7 = 6\7
Cents
Octave-complement intervals represented as s¢ follow this relation s1 + s2 = 1200. For given s, the unknown x can be calculated by the formula x := 1200 - s.
- Examples
- 333¢ vs. (1200-333)¢ = 867¢
- 701.955¢ vs. (1200-701.955)¢ = 498.045¢
See also
- Octave reduction
- Fifth complement -- the analogue for the fifth (3/2)
- Fourth complement -- the analogue for the fourth (4/3)
- Tritave complement -- the analogue for the tritave (3/1)