low-pitched, subdued
你声音怎么听起来这么低沉
Why does your voice sound so deep?
— 完美陌生人 (2016)
他很低沉
His voice is very deep.
— 倩女幽魂 (1987)
只是说人唱歌嗓音比较低沉
It just means that the person has a relatively deep singing voice.
— 放牛班的春天 (2004)