View source for Ploidacot/Omega-pentacot

{{Breadcrumb}}{{Infobox ploidacot|Ploids=1|Shears=4|Cots=5|Pergen=[P8, P4/5]|Forms=12, 13, 25, 37|Title=Omega-pentacot (delta-pentacot)|Wedgie=5}}
'''Omega-pentacot''' is a temperament archetype where the generator is a semitone, five of which stack to form a perfect fourth of [[4/3]], and the period is a [[2/1]] octave. Omega-pentacot temperaments usually generate the [[1L&nbsp;11s]] and [[12L&nbsp;1s]] MOS structures. Regular temperaments of omega-pentacot are [[Cluster MOS|cluster temperaments]] with 12 clusters of notes in an octave.

== Intervals and notation ==
While there is no agreed-upon notation system for omega-pentacot, the following is based on interpreting the generator as a semitone (1/5 of a fourth), allowing for an ^ or v to stand for 1/5 of an ''inversed'' diminished second (the difference between diatonic semitone and chromatic semitone, equivalent to the [[Pythagorean comma]]), so vvvC# and ^^Db are enharmonic.

{| class="wikitable"
|+ style="font-size: 105%;" | Omega-pentacot intervals (assuming pure fifth and octave)
|-
! #
! Cents
! Notation
! Name
|-
| −30
| 611.730
| F#
| augmented fourth
|-
| −29
| 711.339
| ^^G
| 
|-
| −28
| 810.948
| vG#
| 
|-
| −27
| 910.557
| ^A
| 
|-
| −26
| 1010.166
| vvA#
| 
|-
| −25
| 1109.775
| B
| major seventh
|-
| −24
| 9.384
| ^^C
| 
|-
| −23
| 108.993
| vC#
| 
|-
| −22
| 208.602
| ^D
| 
|-
| −21
| 308.211
| vvD#
| 
|-
| −20
| 407.820
| E
| major third
|-
| −19
| 507.429
| ^^F
| 
|-
| −18
| 607.038
| vF#
| 
|-
| −17
| 706.647
| ^G
| 
|-
| −16
| 806.256
| vvG#
| 
|-
| −15
| 905.865
| A
| major sixth
|-
| −14
| 1005.474
| ^^Bb
| 
|-
| −13
| 1105.083
| vB
| 
|-
| −12
| 4.692
| ^C
| 
|-
| −11
| 104.301
| vvC#
| 
|-
| −10
| 203.910
| D
| major second
|-
| −9
| 303.519
| ^^Eb
| 
|-
| −8
| 403.128
| vE
| 
|-
| −7
| 502.737
| ^F
| 
|-
| −6
| 602.346
| vvF#
| 
|-
| −5
| 701.955
| G
| perfect fifth
|-
| −4
| 801.564
| ^^Ab
| 
|-
| −3
| 901.173
| vA
| 
|-
| −2
| 1000.782
| ^Bb
| 
|-
| −1
| 1100.391
| vvB
| 
|-
| 0
| 0.000
| C
| perfect unison
|-
| 1
| 99.609
| ^^Db
| 
|-
| 2
| 199.218
| vD
| 
|-
| 3
| 298.827
| ^Eb
| 
|-
| 4
| 398.436
| vvE
| 
|-
| 5
| 498.045
| F
| perfect fourth
|-
| 6
| 597.654
| ^^Gb
| 
|-
| 7
| 697.263
| vG
| 
|-
| 8
| 796.872
| ^Ab
| 
|-
| 9
| 896.481
| vvA
| 
|-
| 10
| 996.090
| Bb
| minor seventh
|-
| 11
| 1095.699
| ^^Cb
| 
|-
| 12
| 1195.308
| vC
| 
|-
| 13
| 94.917
| ^Db
| 
|-
| 14
| 194.526
| vvD
| 
|-
| 15
| 294.135
| Eb
| minor third
|-
| 16
| 393.744
| ^^Fb
| 
|-
| 17
| 493.353
| vF
| 
|-
| 18
| 592.962
| ^Gb
| 
|-
| 19
| 692.571
| vvG
| 
|-
| 20
| 792.180
| Ab
| minor sixth
|-
| 21
| 891.789
| ^^Bbb
| 
|-
| 22
| 991.398
| vBb
| 
|-
| 23
| 1091.007
| ^Cb
| 
|-
| 24
| 1190.616
| vvC
| 
|-
| 25
| 90.225
| Db
| minor second
|-
| 26
| 189.834
| ^^Ebb
| 
|-
| 27
| 289.443
| vEb
| 
|-
| 28
| 389.052
| ^Fb
| 
|-
| 29
| 488.661
| vvF
| 
|-
| 30
| 588.270
| Gb
| diminished fifth
|}

A notable feature of omega-pentacot is the small comma, encountered after 12 steps, which represents one-fifth of a Pythagorean comma (or its equivalence, ''inversed'' diminished second). This makes omega-pentacot scales cluster around [[12edo]].

== Temperament interpretations ==
=== Quinticular ===
{{See also| Quinticular comma }}

Omega-pentacot temperaments are generally interpretated as quinticular temperaments; the generator is [[18/17]], five of them gives 4/3, so the [[quinticular comma]] (1419857/1417176) is tempered out. 

=== Quintilischis ===
{{See also| Schismatic family }}

In quintilischis, the generator is 18/17, three of which make [[19/16]], five make 4/3, and 40 make [[10/1|10th harmonic]] in the 2.3.5.17.19 subgroup, so [[4624/4617]], [[6144/6137]], and [[6885/6859]] are tempered out. This temperament is a weak extension of [[schismic]], splitting the fourth in five. In the 2.3.5.7.17.19 subgroup, tempering out [[400/399]] (equating 20/19 and 21/20) leads to [[quintilipyth]] (12 &amp; 253), and tempering out [[476/475]] (equating 19/17 with 28/25) leads to [[quintaschis]] (12 &amp; 289).  

=== Quindromeda ===
{{Main| Quindromeda family }}

In [[quindromeda]], the generator is 18/17, three of which make 19/16, five make 4/3, and 28 make [[5/1|5th harmonic]] in the 2.3.5.17.19 subgroup, so [[1216/1215]], [[1445/1444]], and [[6144/6137]] are tempered out. Equating 225/224 with 256/255 leads to [[quintakwai]] (12 &amp; 193), which tempers out 400/399 (also equating 20/19 and 21/20) in the 2.3.5.7.17.19 subgroup, and 361/360 with 400/399 leads to [[quintagar]] (12 &amp; 217), which tempers out 476/475 (also equating 19/17 with 28/25) in the 2.3.5.7.17.19 subgroup. 

=== Quintaleap ===
{{Main| Quintaleap family }}

In [[quintaleap]], the generator is 18/17, three of which make 19/16, five make 4/3, and 16 make [[5/2]] in the 2.3.5.17.19 subgroup, so [[256/255]], [[361/360]], and [[4624/4617]] are tempered out. In the 2.3.5.7.17.19 subgroup, tempering out 400/399 leads to [[quintupole]] (12 &amp; 121), and tempering out 476/475 leads to [[quinticosiennic]] (12 &amp; 145).

=== Passion ===
{{Main| Passion family }}

In [[passion]], the generator is [[16/15]], four of which make [[5/4]], and five make 4/3. It is best tuned with a slightly flat generator of about 98.7{{c}}, and follows that both 3 and 5 should be tuned sharp. The canonical mapping of 7 places [[7/4]] at 10 generators, and follows that the generator should be tuned flatter (about 98.1{{c}}).

=== Ripple ===
{{Main| Ripple family }}

In [[ripple]], the generator is [[27/25]], five of which make 4/3, and eight make [[8/5]]. It is best tuned with a sharp generator of about 101–102{{c}}, giving the [[11L 1s]] MOS structure (rather than 1L 11s), and follows that 3 should be tuned flat.

[[Category:Ploidacots|Omega-pentacot]]