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The '''equal division of the tritave''' or '''twelfth''' ('''EDT''') or '''3rd harmonic''' ('''ED3''') is a [[tuning]] obtained by dividing the [[3/1|3rd harmonic]] in a certain number of [[equal]] steps.  
The '''equal division of the tritave''' or '''twelfth''' ('''EDT''') or '''3rd harmonic''' ('''ED3''') is a [[tuning]] obtained by dividing the [[3/1|3rd harmonic]] in a certain number of [[equal]] steps.  


== Introduction ==
== Introduction to tritave equivalence ==
Western music generally revolves around the principle of [[octave equivalence]]: notes an octave apart are often perceived in western music as being the same ''chroma'' but differing in pitch height. As the octave corresponds to a 2/1 frequency ratio, it has been proposed that the next-simplest after the octave, the 3/1, can also be used to evoke a sense of chroma equivalence. This interval corresponds to a perfect twelfth in the diatonic scale, but when used to refer to an equivalence interval it is often called the "[[tritave]]".
Western music generally revolves around the principle of [[octave equivalence]]: notes an octave apart are often perceived in western music as being the same ''chroma'' but differing in pitch height. As the octave corresponds to a 2/1 frequency ratio, it has been proposed that the next-simplest after the octave, the 3/1, can also be used to evoke a sense of chroma equivalence. This interval corresponds to a perfect twelfth in the diatonic scale, but when used to refer to an equivalence interval it is often called the "[[tritave]]".


It has been argued that pitches a tritave apart can never truly be heard as equivalent in all of the ways that octaves are, with some claiming that the [http://www.mmk.ei.tum.de/persons/ter/top/octequiv.html tonotopic representation of the mammalian auditory system]{{dead link}} is inherently biased towards octave-equivalence. With proper context, experience, and training, however, at least some people find that they can experience some degree of tritave equivalence, especially when using timbres (such as clarinets) whose overtones consist of primarily odd harmonics. It is not known whether odd harmonics actually facilitate the ability to hear in tritave-equivalence. Either way, it is certain that musically valuable organizations of pitch can arise through the equal division of non-octave intervals, regardless of whether the period is perceived as being truly chroma-equivalent, and as such the multitude of equal divisions of the tritave are rich and ripe for exploration.
It has been argued that pitches a tritave apart can never truly be heard as equivalent in all of the ways that octaves are, with some claiming that the [http://www.mmk.ei.tum.de/persons/ter/top/octequiv.html tonotopic representation of the mammalian auditory system]{{dead link}} is inherently biased towards octave-equivalence. With proper context, experience, and training, however, at least some people find that they can experience some degree of tritave equivalence, especially when using timbres whose overtones consist of primarily or only odd harmonics such as clarinets, square waves, or triangle waves. While is not known whether odd harmonics actually facilitate the ability to hear in tritave-equivalence, it is known that musically valuable organizations of pitch can arise through the equal division of non-octave intervals, regardless of whether the period is perceived as being truly chroma-equivalent, and as such the multitude of equal divisions of the tritave are rich and ripe for exploration.


The [[Bohlen–Pierce scale]], most commonly consisting of 13 equal divisions of the tritave (although a justly-intoned version exists as well), seems to have been the second such arrangement to be seriously studied and made into music, the first being the [[Obikhod]] pitch set of the Russian Orthodox Church which seems to have been by extension of the diatonic scale. The BP scale was independently discovered by Heinz Bohlen, John Pierce and Kees Van Prooijen. Bohlen found it while looking for triads with equal-difference tones, Prooijen uncovered it while searching for equally-tempered scales with accurate higher harmonics, and Pierce stumbled upon it trying to find consonant chords other than 4:5:6. Though they all started with different goals in mind, each of them amazingly ended up at the same destination.
The [[Bohlen–Pierce scale]], most commonly consisting of 13 equal divisions of the tritave (although a justly-intoned version exists as well), seems to have been the first such arrangement to be seriously studied and made into music. The BP scale was independently discovered by Heinz Bohlen, John Pierce and Kees Van Prooijen. Bohlen found it while looking for triads with equal-difference tones, Prooijen uncovered it while searching for equally-tempered scales with accurate higher harmonics, and Pierce stumbled upon it trying to find consonant chords other than 4:5:6. Though they all started with different goals in mind, each of them amazingly ended up at the same destination.
 
== Rank two temperaments ==
{{Todo|cleanup|inline=1|text=Rewrite for clarity}}
 
If factors of two are eliminated, the search for consonant intervals begins with the odd harmonic series, 1:3:5:7:9:.... We can take the second tritave of the series, 3:5:7:9, and find within it the two [[isoharmonic]] triads 3:5:7 and 5:7:9; the analogy here is with the third octave of the full harmonic series, 4:5:6:7:8, and the isoharmonic triad 4:5:6, the foundation of triadic harmony in [[5-limit]] theory. Hence, 3:5:7 or 5:7:9 can be viewed as the fundamental consonant triad of no-twos music, and if we then apply the 5-limit analogy one more time, these triads are bounded by the intervals [[7/3]] or [[9/5]] respectively, either of them filling the role of the "fifth" in diatonicism.
 
The standard [[Bohlen–Pierce]] theory takes 3:5:7 to be the fundamental triad, and therefore naturally goes together with scales generated by 7/3, or equivalently 9/7 (the latter being convention), against the tritave. 7/3 generates pentatonic ({{sl|4L 1s}}) and enneatonic ({{sl|4L 5s}}) [[MOS]] scales, and therefore the enneatonic, known as the "Lambda" scale, can be seen as the analog of the diatonic scale. As generators of the Lambda scale run from [[9edt|7\9]] to [[4edt|3\4]], [[13edt]] is the smallest equal temperament supporting it, and can be seen as an equivalent of [[12edo]]. However, 13edt's accuracy in the [[3.5.7 subgroup]] is much better than 12edo's in the 5-limit, more comparable to that of [[31edo]]. Therefore, higher multiples of 13edt remain excellent 3.5.7 subgroup tunings as well, and can be used to introduce higher harmonics ([[39edt]] is especially notable in this regard, with a good representation of both the [[11/9|11th]] and [[13/9|13th]] harmonics).
 
The linear temperament generated by 7/3 that is satisfied in 13edt's 3.5.7 subgroup representation is [[Bohlen–Pierce–Stearns]], which tempers out the comma [[245/243]] and thereby equates the interval [[5/3]] to two generators down ([[81/49]] considering tritave-reduction)—therefore flattening 7/3 by a fraction of this comma. It is also the {{nowrap|4 & 9}} temperament in the 3.5.7 subgroup, and for these reasons serves a function very analogous to that of [[meantone]] in the 5-limit.
 
If we instead take [[9/5]], or more simply [[5/3]], as a generator, the temperament supported by 13edt is [[Arcturus]], which equates 7/3, two tritaves up (i.e. [[21/1]]) to six steps of 5/3. Naively, 5/3 as generator would be the most natural application of the [[Pythagorean tuning|Pythagorean]] principle of using the next higher prime harmonic (5) as a generator against the tritave. However, a larger MOS scale is needed to get full use out of the 7th harmonic, and due to the proximity of 5/3 to half the tritave, most simple MOS scales of Arcturus are quite hard. It is advisable to use ({{sl|2L 9s}}) or ({{sl|2L 11s}}) scales—and therefore, higher EDTs such as [[28edt]] or [[43edt]].
 
Moving through the scales of 13edt, we find the temperament [[Sirius]], defined so that two generator-steps represent [[7/5]] and three represent [[5/3]]; therefore the comma [[3125/3087]] is tempered out and the generator represents [[25/21]]. The smallest complete proper MOS of Sirius is the hard [[6L 1s (3/1-equivalent)|6L 1s]], though some say that it is disadvantageous to have a non-octave scale with a single step of distinct size from the others, because it creates a strong sense of a second equal division of a ''y'' (in this case, [[25/9]]) less than 3/1 and therefore competes with the relatively fragile tritave equivalence. If this "problem" has not been named yet, "cross-equivalence artifacting" would be a perfect name for it. Otherwise, the 13-note MOS of Sirius, [[6L 7s (3/1-equivalent)|6L 7s]], is usable although this is very soft and close to 13edt in good tunings.
 
At higher accuracies, the rank two 3.5.7 temperament tempering out 16875/16807 called [[Canopus]] begins to predominate. This has a mapping [{{val|1 3 3}}, {{val|0 -5 -4}}] and a pure-tritaves TE generator a slightly flat 7/5 at 581.512 cents; the temperament's property is that four 7/5s reach [[27/7]]. This can be extended, notably, to include the fractional harmonic [[11/4]], which is quite close to three 7/5s. This has MOS of size 3, 4, 7, 10, 13, 23, 36, etc, with the 36 note MOS being particularly even.
 
The final interval which 13EDT can reasonably use to generate a rank two temperament is its false 3/2 of 5 degrees. By a weird coincidence, it will generate the {{sl|5L 3s}} unfair father octatonic scale just as if it were an interval of an edo, except that the scale will not always contain a false 4/3 as it must in an EDO. This means, most importantly, that 16/15 cannot be assumed to be a "comma" tempered out by this false Father temperament when it is taken as a temperament of full just intonation. By a second, and totally separate, weird coincidence, the well-known Bohlen–Pierce temperament is its index-2 subtemperament.
 
Due to its 9/7 generator, the temperament which is to BP what neutral temperaments are to syntonic temperaments does not become intelligibly a division of the tritave until extended to 17 tones whereas EDOs supporting various neutral temperaments have an "ordinary" heptatonic scale which is intelligibly a division of the octave. Additionally, 7 and 9 being consecutive odd numbers means that trying to force this temperament into a no-twos subgroup induces very poor "approximations" of less intelligible higher harmonics. To avoid this, this temperament should be assumed to be a temperment of the 3.5.7.8 subgroup tempering out 245/243 and 64/63, the familiar comma from EDOs supporting the [[Superpyth]]agorean or [[Parapyth]]agorean diatonic scale.
 
Among the EDTs tempering out 245/243, 13EDT stands out. An apt analogy can be drawn with EDOs supporting meantone: 4EDT and 9EDT are to BP what 5EDO and 7EDO are to meantone. However, in contrast to meantone, the simplest EDT supporting the BP nonatonic scale—13EDT, the traditional tempered BP scale—is the most accurate and lowest in tuning error until 56EDT. However, there are many EDTs supporting BP temperament which also support extensions to higher-limit temperaments; in particular 2, 3, and 4 times 13 in the form of {{EDTs| 26, 39, and 52 as well as 56EDT.}} For tempering out 16875/16807, 13EDT again stands out, though much better accuracy can be found in more complex divisions such as 114EDT or 127EDT. All of this explains the focus on 13EDT to the exclusion of other EDTs among practitioners of the art of nonoctave composition, but it must be noted that the analysis is only valid if consideration is confined to the 7-limit, which is exactly analogous to confining it to the 5-limit with EDOs. There's a whole other world out there which has not been much explored.
 
For example, [[User:CompactStar|CompactStar]] suggested the alternative fundamental chord 11:13:15 to avoid the highly-dissonant [[7/5]] tritone present in the simpler 3:5:7 chord, with the best temperament for this being [[Electra]] temperament. 15EDT very well approximates the 5th and 13th harmonics, and 12EDT, the 13th and 17th. 39EDT makes for a fine 3.5.7.11.13 system, tempering out 245/243, 275/273, 847/845 and 1331/1343, and so supporting among other things the [{{val|13 19 23 0 2}}, {{val|0 0 0 1 1}}] temperament supported by the whole suite of 13nEDTs: 13, 26, 39, 52, 65, 78 etc.
 
'''One should bear in mind that, in the world of tritave equivalence, ratios of 3 in the denominator are fungible instead of those of 2.''' For example, while the octave-reduced fifth harmonic is 5:4, the tritave-reduced fifth harmonic would be 5:3 instead, which would be a "major sixth" by conventional pitch class terminology.


== As generator chains for temperaments ==
There are other uses, or conceptualizations, of tritave-based tunings. Purely intuitive use of these myriad, assuredly xenharmonic structures comes to mind (see "EDO" versus "equal temperament"). Another intent might be to find or define temperaments (such as Magic, Hanson, etc.), or to provide exact formulae for stretching/compressing what would musically be used as an "ordinary" octave of ~2:1. (And given the stable nature of octave-based systems, some aesthetic overlap even in the most tritave-equivalent of music, would be forseeable.) For instance, the Bernhard-Stopper (19edt) temperament, might for instance be found useful in tuning pianoforti, being equivalent to 12edo, except for a 1.2 cents sharp octave which is relevant to inharmonicity.
There are other uses, or conceptualizations, of tritave-based tunings. Purely intuitive use of these myriad, assuredly xenharmonic structures comes to mind (see "EDO" versus "equal temperament"). Another intent might be to find or define temperaments (such as Magic, Hanson, etc.), or to provide exact formulae for stretching/compressing what would musically be used as an "ordinary" octave of ~2:1. (And given the stable nature of octave-based systems, some aesthetic overlap even in the most tritave-equivalent of music, would be forseeable.) For instance, the Bernhard-Stopper (19edt) temperament, might for instance be found useful in tuning pianoforti, being equivalent to 12edo, except for a 1.2 cents sharp octave which is relevant to inharmonicity.


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; 300 and beyond
; 300 and beyond
* [[316edt]], [[372edt]], [[415edt]], [[499edt]], [[527edt]], [[613edt]], [[729edt]], [[953edt]], [[1342edt]], [[1213edt]], [[3401edt]], [[27208edt]]
* [[314edt|314]], [[316edt|316]], [[336edt|336]], [[372edt|372]], [[415edt|415]], [[428edt|428]], [[499edt|499]], [[527edt|527]], [[613edt|613]], [[729edt|729]], [[800edt|800]], [[953edt|953]], [[1213edt|1213]], [[1342edt|1342]], [[3401edt|3401]], [[6181edt|6181]], [[27208edt|27208]]


* A [[list of tritave reduced harmonics]] for easy comparison of JI and temperaments in tritave-based systems.
* A [[list of tritave reduced harmonics]] for easy comparison of JI and temperaments in tritave-based systems.
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It is useful to consider EDTs that both ''closely'' and ''poorly'' approximate EDOs. The former are usable as stretches and compressions of EDOs with strong flat or sharp tendencies, while the latter allow for no-twos harmony without the distraction of octaves appearing. It is possible to define "dual-octave" EDTs similar to dual-fifth EDOs, as those whose closest approximation of 2 is more than 1/3 of a step off (so in other words, they have a better closest approximation of the 4th harmonic than the 2nd).  
It is useful to consider EDTs that both ''closely'' and ''poorly'' approximate EDOs. The former are usable as stretches and compressions of EDOs with strong flat or sharp tendencies, while the latter allow for no-twos harmony without the distraction of octaves appearing. It is possible to define "dual-octave" EDTs similar to dual-fifth EDOs, as those whose closest approximation of 2 is more than 1/3 of a step off (so in other words, they have a better closest approximation of the 4th harmonic than the 2nd).  


Otherwise, one can speak of EDTs that correspond to a diatonic [[val]] (i.e. the EDT's size is some EDO added to an approximation of [[3/2]] in that EDO that is a [[5L 2s|diatonic]] generator), which is equivalent to the EDT's approximation of [[2/1]] generating the {{sl|8L 3s}} scale against the tritave, therefore being between 5\8edt and 7\11edt.  
Otherwise, one can speak of EDTs that correspond to a diatonic [[val]] (i.e. the EDT's size is some EDO added to an approximation of [[3/2]] in that EDO that is a [[5L 2s|diatonic]] generator), which is equivalent to the EDT's approximation of [[2/1]] generating the {{mos scalesig|8L 3s<3/1>|link=1}} scale against the tritave, therefore being between 5\8edt and 7\11edt.  


EDTs with this property include {{EDTs| 19, 27, 30, 35, 38, 41, 43, 46, 49, 51, 52, 54, 57, 59, 60, 62, 63, 65, 67, 68, 70, 71, 73 to 76, 78, 79, 81 to 87, and all greater than 88.}}  
EDTs with this property include {{EDTs| 19, 27, 30, 35, 38, 41, 43, 46, 49, 51, 52, 54, 57, 59, 60, 62, 63, 65, 67, 68, 70, 71, 73 to 76, 78, 79, 81 to 87, and all greater than 88.}}  
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* [[Consistency levels of small EDTs]]
* [[Consistency levels of small EDTs]]
* [[Relative errors of small EDTs]]
* [[Relative errors of small EDTs]]
* [[Tritave Reduced Harmonics]]
* [[List of tritave reduced harmonics]]
* [[No-twos 31-limit]]
* [[List of no-twos chords in JI]]
* [[List of no-twos chords in JI]]
* Heinz Bohlen's work: [http://www.huygens-fokker.org/bpsite/otherscales.html ''The Bohlen-Pierce Site: Other Unusual Scales'']
* Heinz Bohlen's work: [http://www.huygens-fokker.org/bpsite/otherscales.html ''The Bohlen-Pierce Site: Other Unusual Scales'']


[[Category:Edt| ]] <!-- main article -->
[[Category:Edt| ]] <!-- main article -->
[[Category:Equal-step tuning]]
[[Category:Edonoi]]
[[category:Nonoctave]]
[[Category:Tritave]]
[[Category:Tritave]]
[[Category:Tritave-equivalent temperaments]]
[[Category:Acronyms]]
[[Category:Acronyms]]
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