The term 'subdued sound' refers to a type of sound that is quiet and not very loud. This can include murmurs, undertones, whispers, and mutters. A MURMUR is a low, continuous sound, like the sound of a river or a WHISPER. An UNDERTONE is a low, quiet sound that is heard beneath a louder sound. A WHISPER is a soft, quiet sound made by speaking very quietly. Lastly, a MUTTER is a low, indistinct sound made by speaking quietly or grumbling. All of these sounds are considered to be subdued and are usually used to describe a quiet atmosphere.