Diaschisma: Difference between revisions

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In the progression, the bassline moves as follows: D-(up 5/4)-F#-(down 4/3)-C#-(down 4/3)-G#-(up 5/4)-C-(up 4/3)-G-(up 3/2)-D (*). If we ignore octaves, the first three steps (cumulatively D to G#) moves us up by the tritone [[45/32]], and the last three steps (cumulatively G# to D) are the same moves as the first three, thus it moves us up by the tritone 45/32 a second time. In pure JI, since 45/32 is flat of 600c, each cycle of this progression (*) would shift the tonic down by the diaschisma, which is (2/1) / (45/32)^2 = 2048/2025. The fact that the D we come back to is exactly the same as the first D, indicates that the basic 5-limit intervals, 5/4 and 3/2, are adjusted, or tempered, such that a stack of two 45/32 tritones is sharpened up to the octave 2/1. In temperament contexts, we see this as equivalent to saying that their difference, the diaschisma, is tempered out.

This also ~~implies~~ that ~~there is~~ an interval that is equal to exactly half of an octave‚ namely the tempered 45/32 tritone. Thus all edos (such as [[12edo]], [[22edo]], [[34edo]] and [[46edo]]) and MOS scale structures (such as the MOS scales of [[diaschismic family|diaschismic]] and [[pajara]]) that temper out the diaschisma split the octave into two equal parts; in particular, all diaschismic edos are even-numbered edos.

This also tells us that if a system tempers out the diaschisma, it has an interval that is equal to exactly half of an octave‚ namely the tempered 45/32 tritone. Thus all edos (such as [[12edo]], [[22edo]], [[34edo]] and [[46edo]]) and MOS scale structures (such as the MOS scales of [[diaschismic family|diaschismic]] and [[pajara]]) that temper out the diaschisma split the octave into two equal parts; in particular, all diaschismic edos are even-numbered edos.

== See also ==

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 In the progression, the bassline moves as follows: D-(up 5/4)-F#-(down 4/3)-C#-(down 4/3)-G#-(up 5/4)-C-(up 4/3)-G-(up 3/2)-D (*). If we ignore octaves, the first three steps (cumulatively D to G#) moves us up by the tritone [[45/32]], and the last three steps (cumulatively G# to D) are the same moves as the first three, thus it moves us up by the tritone 45/32 a second time. In pure JI, since 45/32 is flat of 600c, each cycle of this progression (*) would shift the tonic down by the diaschisma, which is (2/1) / (45/32)^2 = 2048/2025. The fact that the D we come back to is exactly the same as the first D, indicates that the basic 5-limit intervals, 5/4 and 3/2, are adjusted, or tempered, such that a stack of two 45/32 tritones is sharpened up to the octave 2/1. In temperament contexts, we see this as equivalent to saying that their difference, the diaschisma, is tempered out.
-This also implies that there is an interval that is equal to exactly half of an octave‚ namely the tempered 45/32 tritone. Thus all edos (such as [[12edo]], [[22edo]], [[34edo]] and [[46edo]]) and MOS scale structures (such as the MOS scales of [[diaschismic family|diaschismic]] and [[pajara]]) that temper out the diaschisma split the octave into two equal parts; in particular, all diaschismic edos are even-numbered edos.
+This also tells us that if a system tempers out the diaschisma, it has an interval that is equal to exactly half of an octave‚ namely the tempered 45/32 tritone. Thus all edos (such as [[12edo]], [[22edo]], [[34edo]] and [[46edo]]) and MOS scale structures (such as the MOS scales of [[diaschismic family|diaschismic]] and [[pajara]]) that temper out the diaschisma split the octave into two equal parts; in particular, all diaschismic edos are even-numbered edos.
 == See also ==