The Collaborative International Dictionary of English v.0.48:
low-toned \low-toned\ adj. relatively low in volume; soft; -- of sound; as, making low-toned noises with their mouths that went as an undercurrent of sound. Opposite of loud. Syn: low, subdued, soft. [WordNet 1.5]WordNet (r) 3.0 (2006):
low-toned adj 1: very low in volume; "a low murmur"; "the low-toned murmur of the surf" [syn: low, low-toned]