The phrase is Robert Duncan's from The Truth and Life of Myth, often cited by Burton Hatlen, for whom the phrase was memory matter derived from a treasured conversation with Duncan. Looking at its use in context now, I find the concept of "tone leading" to have unexpectedly complicated semantic properties. Duncan cites both spiritual and scientific registers of meaning. He writes:

Creativity, as I have suggested, means such a change in the meaning of every part in the creation of each part that every new strictness is also a charm undoing all previous strictnesses, at once an imperative and at the same time a change of imperative. Each syllable of the poem, if we keep alive each sound in the sounding of the whole, is such a stricture—just the sound it is—that proves in the movement of the poem to be a liberation. But let us take this concrete immediacy of the poem: I start with the word "Father," and since I compose by the tone leading of the vowels, the vowels are notes of a scale, in which breaths move, and these soundings of spirit upon which the form of the poem depends are not constant. ” (67).

The "movement of the poem" is "undoing" of existing relations among the parts. Movement on the semantic plane is associated with movement among vowel signs. The effect at the level of the syllable is liberating, balancing vowel duration with the "concrete immediacy" of consonants.

The passage cited from the Truth and Life of Myth is from 1968; conjoined with essays from the same period by Robert Creeley in his A Quick Graph, especially "'Poems are a complex'" (1965), provides guidance with respect to the musical and semantic registers that characterize much of the significant poetry of the seventies. My intention is to explore a bundle of emerging possibilities: Jerome Rothenberg's The Notebooks" and John Taggart's Dodeka  from Membrane (Karl Young's leading-edge press in Milwaukee), Susan Howe's Pythagorean Silences and Gustav Sobin's Wind Chrysalid's Rattle and Celebration of the Sound Through (from Eliot Weinberger's pioneering Montemora). I will also look at Hejinian's Gesualdo and Writing as an Aid to Memory (also Tuumba, 1978) and Michael Davidson's, The Prose of Fact (The Figures 1981). This range of small presses and the talents that they supported represent aspects of the  heart of alternative publishing in the 1970s. They are among the sources of my own publishing and editorial projects beginning with O.ARS in 1980.