Tonality flux

Tonality flux is Harry Partch's term[1] 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.

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 (given here in Ben Johnston's pitch notation): 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.

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.