Has anyone noticed that audio levels on DTV stations can vary widely...I am riding the gain on my remote more often these days and I seem to have to turn up the sound more too...sound processing different than the old analog?

I've found this true both over-the-air and on cable. Audio levels are all over the place.

It's called "dynamic range", the ability to hear loud and soft passages of music, as they were originally intended, as you would in a concert hall. Now that we have a nice little Dolby system to work with, we can have all kinds of things like that! Many systems have a "defeat" button.

I have noticed this. For instance, right now 16.1 is louder than 16.2 or 16.3. The other night I was watching a moving on 49.1 and the audio was much lower than the commercials. I have observed this on other DTV channels.

My HDTV has a selectable audio compressor with three different levels, none, mild, and most. I'm not sure if this works in surround mode or not since I've never hooked up more than two speakers and always just run it in stereo.

Possibly this was never noticed before due to heavier audio processing on analog channels compared to surround on digital?

I know in radio we intentionally put less audio compresson on the HD channels. More dynamic range is just fine in a moving vehicle when there is no multipath.

Get used to it.
It is due to several things.
1. Many sources no longer are in analog mode. They arrive at stations (most commercials and some programs) digitally as a file and they are transferred to the servers with no adjustments to the video and audio unless they are converted to analog and then dubbed back to digital....which normally does not happen. Guess what? There are no standards for audio levels. They are what they are. Video is a little better.

2. When played out, they may not go to analog..depends on the station and their system. Levels don't get adjusted.

3. Dolby Surround Sound. With this wonderful audio, there is still no standard the way it is delivered relative to other sources and it is generally not processed, even in the analog realm. What processing there is may not be as tight as is done with normal/previous sources. Mono signals are not as bad.

4. Usually, the switcher does not have individual level controls for each source. Only one master level adjustment. Normally, those are set and are not adjusted for each source...just left at a master level. Different levels from different sources get passed on. There is more limiting/compression in the analog chain and that will tighten the levels up. Levels coming out of the audio follow video switcher can be all over the map when listening to line out but listening off air in mono seem to be fairly consistent... on analog. not so on DTV. Better than line out but not as tight as analog tv.

There are other reasons but those are some key issues.
The audio problem with digital distribution has been known for some time. Some time ago (1-2 years), someone came and gave a talk at an SBE meeting and warned about the problems we would be facing with digital distribution. It appears that he was correct.

http://etvcookbook.org/audio/dialnorm.html

http://en.wikipedia.org/wiki/Dialnorm

http://broadcastengineering.com/audio/broadcasting_managing_dtv_loudness/

http://www.tvtechnology.com/article/11472

http://www.tvtechnology.com/article/76332

I don't mind the different channels having different levels, that makes sense, but to have to turn up the audio fairly loud to hear the "who done it shows"...to me why can't they do a separate stereo 2 channel processed mix for those most that are viewing television.

Traditionally, the answer to the question, "Why are the commercials louder than the show?", is that it's perceived loudness. It isn't any louder. It's just that the processing is such that it's mostly peaks so it sounds louder by comparison.

This is not "perceived." I've recorded and measured, and actual peak levels vary by almost 20 dB source-to-source on our local ch2 here in Salt Lake.

This has become a real viewer annoyance and a DTV audio reality...now we all got to go and get a 5.1 system to hear properly our television today!