Muffle:
* The thick curtains muffled the sound of the city outside.
* She muffled her sobs into her pillow.
* They muffled the laughter with their hands.
Not muffled:
* The music was not muffled by the crowd's cheers.
* Her voice was clear and not muffled despite the wind.
* The alarm was loud and not muffled by the thick walls.