Sound Quality of Direct TV audio

I don't know but would not surprise me if most digital TV providers do something similar. Most people are not audiophiles who care about full range sound reproduction. Filtering out low bass could well make things sound better for many with lesser gear not capable of delivering high quality low bass and either do not care about low bass or do not know what they might be missing.

Low bass is what makes good quality sound production hard. Filtering it out makes things a lot easier and may well sound better than the alternative with a lot of commercial gear out there.

Wonder if Dish,Comcast do same?

Dish and Direct TV share some satellites, so I would expect the same performance from either one.

That said, what kind of receiver do you have? Maybe its just not that good.

You mention you put the analyzer on the audio outputs of the DirecTV, which implies analog type outputs. That being the case, I wonder if the digital stream, either via HDMI, Toslink Optical or SP/DIF are carrying a full spectrum signal.

Any chance you could try the analyzer on the pre/processor outputs to see if the brick wall is there as well? In that event, we could rule in / out whether they're stripping the spectrum or just doing something with the analog output section of the DTV box.