Hemipyth: Difference between revisions

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A '''hemipyth''' (or '''"hemipythagorean"''') interval is an [[interval]] in the <math>\sqrt{2}\,.\sqrt{3}</math> [[subgroup]] i.e. intervals that can be constructed by multiplying half-integer powers of 2 and 3.
A '''hemipyth''' (or '''"hemipythagorean"''') interval is an [[interval]] in the <math>\sqrt{2}\,.\sqrt{3}</math> [[subgroup]] i.e. intervals that can be constructed by multiplying half-integer powers of 2 and 3.


Notable hemipyth intervals include the neutral third <math>\sqrt{\frac{3}{2}} = \frac{\sqrt{3}}{\sqrt{2}}</math>, semioctave <math>\sqrt{2}</math>, and the semifourth <math>\sqrt{\frac{4}{3}} = \frac{2}{\sqrt{3}}</math>.
Notable hemipyth intervals include the neutral third <math>\sqrt{\frac{3}{2}} = \frac{\sqrt{3}}{\sqrt{2}}</math>, semioctave <math>\sqrt{2}</math>, and the semifourth <math>\sqrt{\frac{4}{3}} = \frac{2}{\sqrt{3}}</math>.


Many temperaments naturally produce intervals that split ~3/2, ~2, or ~4/3 exactly in half and can thus be interpreted as neutral thirds, semioctaves, or semifourths within the temperament.
Many temperaments naturally produce intervals that split ~{{sfrac|3|2}}, ~2, or ~{{sfrac|4|3}} exactly in half and can thus be interpreted as neutral thirds, semioctaves, or semifourths within the temperament.


== Equal temperaments ==
== Equal temperaments ==
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* Either the edo is even and it features at least <math>\sqrt{2}</math> (which is tuned "pure" when the octave is tuned pure).
* Either the edo is even and it features at least <math>\sqrt{2}</math> (which is tuned "pure" when the octave is tuned pure).
* Or one of the following is true:
* Or one of the following is true:
** The closest approximation to 3/2 spans an even number of edosteps (leading to an approximation to <math>\sqrt{\frac{3}{2}}</math>)
** The closest approximation to {{sfrac|3|2}} spans an even number of edosteps (leading to an approximation to <math>\sqrt{\frac{3}{2}}</math>)
** The closest approximation to 4/3 spans an even number of edosteps (leading to an approximation to <math>\sqrt{\frac{4}{3}}</math>)
** The closest approximation to {{sfrac|4|3}} spans an even number of edosteps (leading to an approximation to <math>\sqrt{\frac{4}{3}}</math>)


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== Notation ==
== Notation ==
The Pythagorean (2.3) part of hemipyth can be notated using traditional notation where octaves represent multiples of 2/1, chain of fifths denotes multiples of 3/2, the sharp sign is equal to 2187/2048 etc.
The Pythagorean (2.3) part of hemipyth can be notated using traditional notation where octaves represent multiples of {{sfrac|2|1}}, chain of fifths denotes multiples of {{sfrac|3|2}}, the sharp sign is equal to {{sfrac|2187|2048}} etc.


A prototypical 5L&nbsp;2s 5|1 (Ionian) scale would be spelled C, D, E, F, G, A, B, (C).
A prototypical 5L&nbsp;2s 5|1 (Ionian) scale would be spelled C, D, E, F, G, A, B, (C).
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=== Semioctaves ===
=== Semioctaves ===
In traditional notation the octave spans 7 diasteps which means that it splits into two interordinal {{frac|3|1|2}} diasteps or two perfect 4.5ths ("four-and-a-halves") if we wish to remain backwards compatible with the 1-indexed traditional notation.
In traditional notation the octave spans 7 diasteps which means that it splits into two interordinal {{sfrac|3|1|2}} diasteps or two perfect 4.5ths ("four-and-a-halves") if we wish to remain backwards compatible with the 1-indexed traditional notation.


Intervals retain their quality when the frequency ratio is multiplied by the perfect semioctave <math>\sqrt{2}</math>, e.g. {{nowrap|M6 &minus; P4.5 {{=}} M2.5 {{=}} ({{frac|9|8}})<sup>3/2</sup>}}.
Intervals retain their quality when the frequency ratio is multiplied by the perfect semioctave <math>\sqrt{2}</math>, e.g. {{nowrap|M6 &minus; P4.5 {{=}} M2.5 {{=}} ({{frac|9|8}})<sup>3/2</sup>}}.
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=== Semifourths ===
=== Semifourths ===
Luckily we don't need to introduce any more generalizations to the notation to indicate <math>\sqrt{\frac{4}{3}}</math>. It's a neutral {{frac|2|1|2}} or a α{{demiflat2}} (alp semiflat) w.r.t middle C.
Luckily we don't need to introduce any more generalizations to the notation to indicate <math>\sqrt{\frac{4}{3}}</math>. It's a neutral {{sfrac|2|1|2}} or a α{{demiflat2}} (alp semiflat) w.r.t middle C.


Nicknames are still assigned to make it easier to talk about the [[5L&nbsp;4s]] scale generated by <math>~\sqrt{\frac{4}{3}}</math> against the octave.
Nicknames are still assigned to make it easier to talk about the [[5L&nbsp;4s]] scale generated by <math>\sim\vsp\sqrt{\frac{4}{3}}</math> against the octave.


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The neutral third receives only half of the tuning damage of the fifth so it has a strong character even if the fifth isn't tuned very pure. The irrational nature of <math>\sqrt{\frac{3}{2}}</math> also makes it more tolerant of imprecise tuning.
The neutral third receives only half of the tuning damage of the fifth so it has a strong character even if the fifth isn't tuned very pure. The irrational nature of <math>\sqrt{\frac{3}{2}}</math> also makes it more tolerant of imprecise tuning.


The same goes for the semifourth. A poorly tuned ~4/3 still results in a decent <math>~\sqrt{\frac{4}{3}}</math> (assuming it's featured in the tuning in the first place).
The same goes for the semifourth. A poorly tuned ~{{sfrac|4|3}} still results in a decent <math>\sim\vsp\sqrt{\frac{4}{3}}</math> (assuming it's featured in the tuning in the first place).


=== Signposts ===
=== Signposts ===
Due to their low damage in supporting temperaments, the octave&nbsp;({{frac|2|1}}), semioctave&nbsp;<math>\left(\sqrt{2}\right)</math>, perfect&nbsp;fifth&nbsp;({{frac|3|2}}), perfect&nbsp;fourth&nbsp;({{frac|4|3}}), neutral&nbsp;third&nbsp;<math>\left(\sqrt{\frac{3}{2}}\right)</math>, neutral&nbsp;sixth&nbsp;<math>\left(\sqrt{\frac{8}{3}}\right)</math>, semifourth&nbsp;<math>\left(\sqrt{\frac{4}{3}}\right)</math>, semitwelfth&nbsp;<math>\left(\sqrt{3}\right)</math>, "hemitone"&nbsp;<math>\left(\sqrt{\frac{9}{8}}\right)</math>, and "contrahemitone"&nbsp;<math>\left(\sqrt{\frac{32}{9}}\right)</math> all provide good signposts for navigating around otherwise unfamiliar scales.
Due to their low damage in supporting temperaments, the octave&nbsp;({{sfrac|2|1}}), semioctave&nbsp;<math>\left(\sqrt{2}\right)</math>, perfect&nbsp;fifth&nbsp;({{sfrac|3|2}}), perfect&nbsp;fourth&nbsp;({{sfrac|4|3}}), neutral&nbsp;third&nbsp;<math>\left(\sqrt{\frac{3}{2}}\right)</math>, neutral&nbsp;sixth&nbsp;<math>\left(\sqrt{\frac{8}{3}}\right)</math>, semifourth&nbsp;<math>\left(\sqrt{\frac{4}{3}}\right)</math>, semitwelfth&nbsp;<math>\left(\sqrt{3}\right)</math>, "hemitone"&nbsp;<math>\left(\sqrt{\frac{9}{8}}\right)</math>, and "contrahemitone"&nbsp;<math>\left(\sqrt{\frac{32}{9}}\right)</math> all provide good signposts for navigating around otherwise unfamiliar scales.


While untempered semitones usually come as unequal pairs consisting of an augmented unison and a minor second, the "hemitone" is always exactly the geometric half of a 9/8 whole tone. The "contrahemitone" is its octave-complement.
While untempered semitones usually come as unequal pairs consisting of an augmented unison and a minor second, the "hemitone" is always exactly the geometric half of a {{sfrac|9|8}} whole tone. The "contrahemitone" is its octave-complement.


== Temperament interpretations ==
== Temperament interpretations ==
Under [[ploidacot]] classification diploid temperaments feature <math>~\sqrt{2}</math>, dicot temperaments have <math>~\sqrt{\frac{3}{2}}</math> and alpha-dicot temperaments feature <math>~\sqrt{\frac{4}{3}}</math> (by virtue of having a <math>~\sqrt{3}</math>).
Under [[ploidacot]] classification diploid temperaments feature <math>\sim\vsp\sqrt{2}</math>, dicot temperaments have <math>\sim\vsp\sqrt{\frac{3}{2}}</math> and alpha-dicot temperaments feature <math>\sim\vsp\sqrt{\frac{4}{3}}</math> (by virtue of having a <math>\sim\vsp\sqrt{3}</math>).


Full hemipyth support is indicated by at least "diploid dicot". Examples include:
Full hemipyth support is indicated by at least "diploid dicot". Examples include:
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|+ style="font-size: 105%;" | Higher-prime interpretations of hemipyth intervals
|+ style="font-size: 105%;" | Higher-prime interpretations of hemipyth intervals
|-
|-
! Temperament !! <math>~\sqrt{2}</math> !! <math>~\sqrt{\frac{3}{2}}</math> !! <math>~\sqrt{\frac{4}{3}}</math> !! contorted !! rank-2
! Temperament !! <math>\sim\vsp\sqrt{2}</math> !! <math>\sim\vsp\sqrt{\frac{3}{2}}</math> !! <math>\sim\vsp\sqrt{\frac{4}{3}}</math> !! contorted !! rank-2
|-
|-
| [[decimal]] || ~7/5 || ~5/4 || ~7/6 || no || yes
| [[decimal]] || ~{{sfrac|7|5}} || ~{{sfrac|5|4}} || ~{{sfrac|7|6}} || no || yes
|-
|-
| [[anguirus]] || ~45/32 || ~56/45 || ~7/6 || no || yes
| [[anguirus]] || ~{{sfrac|45|32}} || ~{{sfrac|56|45}} || ~{{sfrac|7|6}} || no || yes
|-
|-
| [[sruti]] || ~45/32 || ~175/144 || ~81/70 || no || yes
| [[sruti]] || ~{{sfrac|45|32}} || ~{{sfrac|175|144}} || ~{{sfrac|81|70}} || no || yes
|-
|-
| [[Subgroup temperaments#Pakkanian hemipyth|pakkanian hemipyth]] || ~17/12 || ~11/9 || ~15/13 || no || yes
| [[Subgroup temperaments#Pakkanian hemipyth|pakkanian hemipyth]] || ~{{sfrac|17|12}} || ~{{sfrac|11|9}} || ~{{sfrac|15|13}} || no || yes
|-
|-
| [[harry]] || ~17/12 || ~11/9 || ~15/13 || yes || yes
| [[harry]] || ~{{sfrac|17|12}} || ~{{sfrac|11|9}} || ~{{sfrac|15|13}} || yes || yes
|-
|-
| [[semimiracle]] || ~91/64 || ~11/9 || ~15/13 || yes || yes
| [[semimiracle]] || ~{{sfrac|91|64}} || ~{{sfrac|11|9}} || ~{{sfrac|15|13}} || yes || yes
|-
|-
| [[hemidim]] || ~36/25 || ~25/21 || ~7/6 || yes || yes
| [[hemidim]] || ~{{sfrac|36|25}} || ~{{sfrac|25|21}} || ~{{sfrac|7|6}} || yes || yes
|-
|-
| [[greenland]] || ~99/70 || ~49/40 || ~15/13~231/200 || no || no
| [[greenland]] || ~{{sfrac|99|70}} || ~{{sfrac|49|40}} || ~{{sfrac|15|13}}~{{sfrac|231|200}} || no || no
|-
|-
| [[semisema]] || ~108/77 || ~11/9 || ~7/6 || no || yes
| [[semisema]] || ~{{sfrac|108|77}} || ~{{sfrac|11|9}} || ~{{sfrac|7|6}} || no || yes
|-
|-
| [[quadritikleismic]] || ~625/441 || ~49/40 || ~125/108 || yes || yes
| [[quadritikleismic]] || ~{{sfrac|625|441}} || ~{{sfrac|49|40}} || ~{{sfrac|125|108}} || yes || yes
|-
|-
| [[decoid]] || ~99/70 || ~49/40 || ~4725/4096 || yes || yes
| [[decoid]] || ~{{sfrac|99|70}} || ~{{sfrac|49|40}} || ~{{sfrac|4725|4096}} || yes || yes
|}
|}


Above contorted tunings don't have a <math>~\sqrt{2}</math> period with a <math>~\sqrt{3}</math> generator, but introduce further splits. Higher than rank-2 temperaments introduce further structure that goes beyond basic hemipyth.
Above contorted tunings don't have a <math>\sim\vsp\sqrt{2}</math> period with a <math>\sim\vsp\sqrt{3}</math> generator, but introduce further splits. Higher than rank-2 temperaments introduce further structure that goes beyond basic hemipyth.


Some possible interpretations for <math>~\sqrt{2}</math> are:
Some possible interpretations for <math>\sim\vsp\sqrt{2}</math> are:


{| class="wikitable"
{| class="wikitable"
|+ style="font-size: 105%;" | Higher-prime interpretations of <math>\sqrt{2}</math>
|+ style="font-size: 105%;" | Higher-prime interpretations of <math>\sqrt{2}</math>
|-
|-
! Temperament !! <math>~\sqrt{2}</math> !! contorted !! rank-2
! Temperament !! <math>\sim\vsp\sqrt{2}</math> !! contorted !! rank-2
|-
|-
| [[jubilic]] || ~7/5 || no || yes (2.5.7)
| [[jubilic]] || ~{{sfrac|7|5}} || no || yes (2.5.7)
|-
|-
| [[diaschismic]] || ~45/32 || no || yes (2.3.5)
| [[diaschismic]] || ~{{sfrac|45|32}} || no || yes (2.3.5)
|-
|-
| [[semitonic]] || ~17/12 || no || yes (2.3.17)
| [[semitonic]] || ~{{sfrac|17|12}} || no || yes (2.3.17)
|-
|-
| [[kalismic temperaments|kalismic]] || ~99/70 || no || no
| [[kalismic temperaments|kalismic]] || ~{{sfrac|99|70}} || no || no
|}
|}


Some possible interpretations for <math>~\sqrt{3}</math> are:
Some possible interpretations for <math>\sim\vsp\sqrt{3}</math> are:


{| class="wikitable"
{| class="wikitable"
|+ style="font-size: 105%;" | Higher-prime interpretations of <math>\sqrt{3}</math>
|+ style="font-size: 105%;" | Higher-prime interpretations of <math>\sqrt{3}</math>
|-
|-
! Temperament !! <math>~\sqrt{3}</math> !! contorted !! rank-2
! Temperament !! <math>\sim\vsp\sqrt{3}</math> !! contorted !! rank-2
|-
|-
| [[semaphore]] || ~7/4 || no || yes (2.3.7)
| [[semaphore]] || ~{{sfrac|7|4}} || no || yes (2.3.7)
|-
|-
| [[barbados]] || ~26/15 || no || yes (2.3.13/5)
| [[barbados]] || ~{{sfrac|26|15}} || no || yes (2.3.{{sfrac|13|5}})
|}
|}


Some possible interpretations for ~√(3/2) are:
Some possible interpretations for <math>\sim\vsp\frac{3}{2}</math> are:


{| class="wikitable"
{| class="wikitable"
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! Temperament !! <math>\sqrt{~\frac{3}{2}}</math> !! contorted !! rank-2
! Temperament !! <math>\sqrt{~\frac{3}{2}}</math> !! contorted !! rank-2
|-
|-
| [[dicot]] || ~5/4 || no || yes (2.3.5)
| [[dicot]] || ~{{sfrac|5|4}} || no || yes (2.3.5)
|-
|-
| [[Rastmic clan#Neutral|neutral]] || ~11/9 || no || yes (2.3.11)
| [[Rastmic clan#Neutral|neutral]] || ~{{sfrac|11|9}} || no || yes (2.3.11)
|-
|-
| [[jove]] || ~11/9~49/40 || no || no
| [[jove]] || ~{{sfrac|11|9}}~{{sfrac|49|40}} || no || no
|}
|}