Adjectives

(s)hushed, muted, subdued, quietin a softened tone“hushed voices”, “muted trumpets”, “a subdued whisper”, “a quiet reprimand”
(s)dull, muffled, muted, softenedbeing or made softer or less loud or clear“the dull boom of distant breaking waves”, “muffled drums”, “the muffled noises of the street”, “muted trumpets”