Tonality flux


Tonality flux is Harry Partch's term for the kinds of subtle harmonic changes that can occur in a microtonal context from notes moving from one chord to another by tiny increments of voice leading. For instance, within a major third G-B, there can be a minor third G to B, such that in moving from one to the other each line shifts less than a half-step. Within a just intonation scale, this could be represented by
Note nameratiocentsinterval name
G1/10Just major third
B5/4386Just major third

moving to
Note nameratiocentsinterval namenameratiocents
G55/5432Just minor thirdG – B6/5316
B11/9347Just minor thirdG – B6/5316

like so:
Note
name		ratiocentsnameratiocents
B5/4386
B11/9347
G55/5432
G1/10

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 composition The Letter, in which the kithara alternates between two chords, one major and one minor, with the minor third of one nestled inside the major third of the other :
In this notation, which assumes G as the tonic or 1/1, a 7 lowers a pitch from a just intonation value by 35/36, 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 notes 8/7, 10/7, and 12/7 ; the second chord is a minor triad comprising the pitches 7/6, 7/5, and 7/4. 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 voice leading.