Tremulous

His tremulous voice betrayed his nervousness.

Source: tatoeba (9935544)

A little more confidence might help you get rid of that tremulous voice.

Source: tatoeba (9948779)

This Inspector, when I first knew him, was a man of fourscore years, or thereabouts, and certainly one of the most wonderful specimens of winter-green that you would be likely to discover in a lifetime’s search. With his florid cheek, his compact figure, smartly arrayed in a bright-buttoned blue coat, his brisk and vigorous step, and his hale and hearty aspect, altogether he seemed—not young, indeed—but a kind of new contrivance of Mother Nature in the shape of man, whom age and infirmity had no business to touch. His voice and laugh, which perpetually re-echoed through the Custom-House, had nothing of the tremulous quaver and cackle of an old man’s utterance; they came strutting out of his lungs, like the crow of a cock, or the blast of a clarion.

Source: tatoeba (12192485)

Tremulous on the bladed graſs ſhone bright the pearly drops, like an aſſembly of ſparkling ſtars dancing on the plains of the zodiac; vocal was every bending ſpray, every reed was inſpired, each warbling throat ſeemed to emulate the melodious voice of the bird of a thouſand ſongs.

Source: wiktionary