Actually, at least a few home theater receivers already do that. Sony's STR DB840, of which I have the 2000 model or so, has a soundfield called "Night Theater" which compresses the volume for late-night viewing when you don't want to disturb the neighbors. It works really well, I've found. I think that model has been discontinued, but I would imagine its replacements retained that functionality.
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Actually, at least a few home theater receivers already do that. Sony's STR DB840, of which I have the 2000 model or so, has a soundfield called "Night Theater" which compresses the volume for late-night viewing when you don't want to disturb the neighbors. It works really well, I've found. I think that model has been discontinued, but I would imagine its replacements retained that functionality.