From Kephart's Our Southern Highlanders:
Kacirk's Informal English, s.v. Holy Tone:
The Call of the South (SBC Home Mission Board, 1918):
to hear another circuit-rider expound and denounce at the top of his voice until late afternoon—as long as "the spirit lasts" and he has "good wind." When he warms up, he throws in a gasping ah or uh at short intervals, which constitutes the "holy tone."
Kacirk's Informal English, s.v. Holy Tone:
A method of utterance, often used in their sermons by Primitive Baptist preachers, in which the sound "ah" occurs at the end of each breath pause, and the taking of fresh breath is intentionally made audible. Also holy whine.
The Call of the South (SBC Home Mission Board, 1918):
In many remote sections the preachers in speaking still affect the sing-song cadences of what has been irreverently dubbed the "holy whine." This rhythmic intonation is pleasant to the ear, and many of the older mountain church members regard this method of delivery by the preacher as a hallmark of downright earnestness and humility. A mountain woman who had been brought up under the recurrent sermonic "a-ahs" of old Brother Jones, after hearing Dr. John A. Broadus, who was reckoned the foremost American Baptist preacher of his day, remarked: "I'd ruther hear Brother Jones...