The phrase "a modest voice" is correct and usable in written English.
It can be used to describe someone who speaks in a humble or unassuming manner, often in contexts discussing communication styles or personal characteristics.
Example: "Despite her achievements, she always spoke with a modest voice, never seeking the spotlight."
Alternatives: "a humble tone" or "a reserved voice".
Mr. Tomlin has a modest voice, full of yearning, but it's not his voice that's important.
Even when displaying his formidable technique and stylistic flexibility, his piano spoke in a modest voice.
In western Europe, organised Christianity often acts as a modest voice in the ranks of the egalitarian left.
Like his partner, Syd, with whom he started a band, called the Internet, in 2011, Martians has a modest voice that he jostles into interesting places; he's more concerned with style and process than with precision.
Against the backdrop of this enforced party line, Joyce is alarmed by the smallest signs that men's rights groups may be gaining even a modest voice in framing domestic violence policy.
That's Sydney, played with a modest voice and a genuine warmth that marks Wayne Alan Wilcox as another talent that should outshine this show.
Mr. El Din's solo pieces were even more unadorned, with single lines of melody, sometimes joined by his singing in a dry, modest voice, and decorated only by his subtly varied attacks on the strings of the oud: rounded tones, precise tremolos or percussive string snapping, as is done on the banjolike Japanese biwa, which he has studied.
Her story – born in Essex, playing the East End music halls as a child, and hitting the new boom industry of radio in the late 1930s – is told in a chirpy but modest voice.
With a warm burr in his modest voice, he can do a credible imitation of Bruce Springsteen, and he started his set with a verse from that Garden State forefather's "Racing in the Streets".
One of the nice things about the bungalows is they have a very quiet, rather modest voice.
In Mr. Manilow's 1970's heyday, no one imagined that his modest voice would give him a second career as an interpreter.
