Kite's thoughts on pergens: Difference between revisions
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Unlike the previous examples, Demeter aka Trizo-agugu's gen2 can't be expressed as a mapping comma. It divides 5/4 into three 15/14 generators, and 7/6 into two generators. Its pergen is (P8, P5, vm3/2). It could also be called (P8, P5, vM3/3), but the pergen with a smaller fraction is preferred. Because the 8ve and 5th are unsplit, single-pair notation is possible, with gen2 = ^m2 and no EU. But the 4:5:6:7 chord would be spelled C -- ^^^Fbbb -- G -- ^^Bbb, very awkward! Standard double-pair notation is better. Gen2 = v/A1, EU = ^^\\\dd3, and ^^\\\C = A##. Genchain2 is C -- v/C# -- \Eb -- vE -- \\Gb -- v\G -- vvG#=\\\Bbb -- v\\Bb... Unlike other genchains we've seen, the additional accidentals get progressively more complex. Whenever an accidental has its own EU, with no other accidentals in it, it always adds up to something simpler eventually. If it doesn't have its own EU, it's infinitely stackable. A case can be made for a convention that colors are used only for infinitely stackable accidentals, and ups/downs/lifts/drops only for the other kind of accidentals. | Unlike the previous examples, Demeter aka Trizo-agugu's gen2 can't be expressed as a mapping comma. It divides 5/4 into three 15/14 generators, and 7/6 into two generators. Its pergen is (P8, P5, vm3/2). It could also be called (P8, P5, vM3/3), but the pergen with a smaller fraction is preferred. Because the 8ve and 5th are unsplit, single-pair notation is possible, with gen2 = ^m2 and no EU. But the 4:5:6:7 chord would be spelled C -- ^^^Fbbb -- G -- ^^Bbb, very awkward! Standard double-pair notation is better. Gen2 = v/A1, EU = ^^\\\dd3, and ^^\\\C = A##. Genchain2 is C -- v/C# -- \Eb -- vE -- \\Gb -- v\G -- vvG#=\\\Bbb -- v\\Bb... Unlike other genchains we've seen, the additional accidentals get progressively more complex. Whenever an accidental has its own EU, with no other accidentals in it, it always adds up to something simpler eventually. If it doesn't have its own EU, it's infinitely stackable. A case can be made for a convention that colors are used only for infinitely stackable accidentals, and ups/downs/lifts/drops only for the other kind of accidentals. | ||
There are always many alternate 2nd generators. Any combination of periods, 1st generators and commas can be added to or subtracted from gen2 to make alternates. If gen2 can be expressed as a mapping comma, that is preferred. For Demeter, any combination of \m3, double-8ves and double-5ths (M9's) makes an alternate multigen2. Any 3-limit interval can be added or subtracted twice, because the splitting fraction is 2. Obviously we can't choose the multigen2 with the smallest cents, because there will always be a 3-limit comma small enough to be subtracted twice from it. Instead, once the splitting fraction is minimized, choose the multigen2 with the smallest odd limit. In case of two ratios with the same odd limit, as 5/3 and 5/4, the '''DOL''' ([[Odd limit|double odd limit]]) is minimized. DOL (5/3) = (5,3) and DOL (5/4) = (5,1). Since 1 < 3, 5/4 is preferred. | There are always many alternate 2nd generators. Any combination of periods, 1st generators and commas can be added to or subtracted from gen2 to make alternates. If gen2 can be expressed as a mapping comma, that is preferred. For Demeter, any combination of \m3, double-8ves and double-5ths (M9's) makes an alternate multigen2. Any 3-limit interval can be added or subtracted twice, because the splitting fraction is 2. Obviously we can't choose the multigen2 with the smallest cents, because there will always be a 3-limit comma small enough to be subtracted twice from it. Instead, once the splitting fraction is minimized, choose the multigen2 with the smallest odd limit. In case of two ratios with the same odd limit, as 5/3 and 5/4, the '''DOL''' ([[Odd limit|double odd limit]]) is minimized. DOL (5/3) = (5,3) and DOL (5/4) = (5,1). Since 1 < 3, 5/4 is preferred. And as a tie-breaker, in case of two ratios with the same DOL (such as 5/3 and 6/5), to minimize the size in cents of the multigen2. Since 5/3 = 884.4¢ and 6/5 = 315.6¢, 6/5 is preferred. | ||
If ^1 = 81/80, possible half-split gen2's are vM3/2, vM6/2, and their octave inverses ^m6/2 and ^m3/2. Possible third-split gen2's are vM3/3, vM6/3, vM2/3, and their inverses, plus vM9/3, ^m10/3 and vM10/3. If ^1 = 64/63, possible third-splits are ^M2/3, vm3/3, ^M3/3, vm6/3, ^M6/3, vm7/3, ^M9/3, vm10/3 and ^M10/3. Analogous to rank-2 pergens with imperfect multigens, there will be occasional double-up or double-down multigen2's. | If ^1 = 81/80, possible half-split gen2's are vM3/2, vM6/2, and their octave inverses ^m6/2 and ^m3/2. Possible third-split gen2's are vM3/3, vM6/3, vM2/3, and their inverses, plus vM9/3, ^m10/3 and vM10/3. If ^1 = 64/63, possible third-splits are ^M2/3, vm3/3, ^M3/3, vm6/3, ^M6/3, vm7/3, ^M9/3, vm10/3 and ^M10/3. Analogous to rank-2 pergens with imperfect multigens, there will be occasional double-up or double-down multigen2's. | ||
All possible rank-3 pergens can be listed, but the table is much longer than for rank-2 pergens. Here are all the half-split pergens: | All possible rank-3 pergens can be listed, but the table is much longer than for rank-2 pergens. Here are all the half-split pergens: | ||
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| | 10 | | | 10 | ||
| | (P8/2, P5, ^m3/2) | | | (P8/2, P5, ^m3/2) | ||
| | half-8ve half-upminor 3rd | | | half-8ve half-upminor-3rd | ||
| | (P8/2, P5, ^M2/2) | | | (P8/2, P5, ^M2/2) | ||
| | half-8ve half-upmajor-2nd | | | half-8ve half-upmajor-2nd | ||
| Line 1,695: | Line 1,695: | ||
| | 11 | | | 11 | ||
| | (P8/2, P5, vM3/2) | | | (P8/2, P5, vM3/2) | ||
| | half-8ve half-downmajor 3rd | | | half-8ve half-downmajor-3rd | ||
| | (P8/2, P5, vm3/2) | | | (P8/2, P5, vm3/2) | ||
| | | | | half-8ve half-downminor-3rd | ||
|- | |- | ||
| | 12 | | | 12 | ||
| | (P8/2, | | | (P8, P4/2, vM3/2) | ||
| | half- | | | half-4th half-downmajor-3rd | ||
| | (P8/2 | | | (P8, P4/2, ^M2/2) | ||
| | | | | half-4th half-upmajor-2nd | ||
|- | |- | ||
| | 13 | | | 13 | ||
| | (P8, P4/2, ^m6/2) | | | (P8, P4/2, ^m6/2) | ||
| | | | | half-4th half-upminor-6th | ||
| | (P8, P4/2, vm7/2) | | | (P8, P4/2, vm7/2) | ||
| | | | | half-4th half-downminor-7th | ||
|- | |- | ||
| | | | | 14 | ||
| | (P8, P5/2, | | | (P8, P5/2, vM3/2) | ||
| | | | | half-5th half-downmajor-3rd | ||
| | (P8, P5/2, ^M2/2) | | | (P8, P5/2, ^M2/2) | ||
| | | | | half-5th half-upmajor-2nd | ||
|- | |- | ||
| | | | | 15 | ||
| | (P8, P5/2, ^m6/2) | | | (P8, P5/2, ^m6/2) | ||
| | | | | half-5th half-upminor-6th | ||
| | (P8, P5/2, vm7/2) | | | (P8, P5/2, vm7/2) | ||
| | | | | half-5th half-downminor-7th | ||
|- | |- | ||
| | | | | 16 | ||
| | (P8/2, P4/2, vM3/2) | | | (P8/2, P4/2, vM3/2) | ||
| | half-everything half-downmajor-3rd | | | half-everything half-downmajor-3rd | ||
| | (P8/2, P4/2, ^M2/2) | | | (P8/2, P4/2, ^M2/2) | ||
| | | | | half-everything half-upmajor-2nd | ||
|} | |} | ||
There are at least 100 third-splits and 287 quarter-splits. More columns could be added for ^1 = 33/32, ^1 = 729/704, ^1 = 27/26, etc. | There are at least 100 third-splits and 287 quarter-splits. More columns could be added for ^1 = 33/32, ^1 = 729/704, ^1 = 27/26, etc. | ||