The sweetest Musick is the Sound of her Voice whom we love.

[L’harmonie la plus douce est le son de voix de celle que l’on aime.]

Jean de La Bruyere
Jean de La Bruyère (1645-1696) French essayist, moralist
The Characters [Les Caractères], ch. 3 “Of Women [Des Femmes],” § 10 (3.10) (1688) [Bullord ed. (1696)]
    (Source)

(Source (French)). Alternate translations:

The sweetest Musick, the Sound of her Voice whom we love.
[Curll ed. (1713)]

The sweetest Musick the Voice of her whom we love.
[Browne ed. (1752)]

The sweetest music is the sound of the voice of the woman we love.
[tr. Van Laun (1885)]

The sweetest music is the sound of the voice of her whom we love.
[tr. Lee (1903)]

No harmony is sweeter than the sound of a loved one's voice.
[tr. Stewart (1970)]