Tonality flux isHarry Partch's term[1] for the kinds of subtleharmonic changes that can occur in amicrotonal context from notes moving from onechord to another by tiny increments ofvoice leading. For instance, within amajor third G-B, there can be aminor third G
to B
, such that in moving from one to the other each line shifts less than ahalf-step. Within ajust intonation scale, this could be represented (, indicates an approximate quarter-tone sharp, an approximate quarter-tone flat) by
| Note name | ratio | cents | interval name |
|---|---|---|---|
| G | 1/1 | 0 | Just major third |
| B | 5/4 | 386 |
moving to
| Note name | ratio | cents | interval name | name | ratio | cents |
|---|---|---|---|---|---|---|
| G | 55/54 | 32 | Just minor third | G – B | 6/5 | 316 |
| B | 11/9 | 347 |
like so:
| Note name | ratio | cents | name | ratio | cents |
|---|---|---|---|---|---|
| B | 5/4 | 386 | |||
| B♭ | 11/9 | 347 | |||
| G | 55/54 | 32 | |||
| G | 1/1 | 0 |
One voice slides down from 386 cents to 347, the other slides up from 0 cents to 32, yet the harmonic shift can be dramatic. The best-known example of tonality flux, and one of the two Partch uses as illustration, is the beginning of his compositionThe Letter, in which thekithara alternates between two chords, onemajor and oneminor, with the minor third of one nestled inside the major third of the other (given here inBen Johnston's pitch notation):
In this notation, which assumes G as thetonic or 1/1, a 7 lowers a pitch from ajust intonation value by35/36, or 48.77 cents; an upside-down 7 raises a pitch by the same amount. The first chord is a major triad and, relative to G, contains the notes8/7 (231 cents above G),10/7 (617 cents), and12/7 (933 cents); the second chord is a minor triad comprising the pitches7/6 (267 cents),7/5 (583 cents), and7/4 (969 cents). Notice that while the outer notes ascend from the first chord to the second, the middle note descends. Such subtle movements were among the attractions that Partch found in an expanded just intonation of more than 12 pitches per octave. Tonality flux is a special instance of the principle of parsimonious (most direct) voice leading.
