Dolby True HD is the only codec that has dialogue normalization built in, but it can be turned off at both ends (encoding or decoding). All reports indicate that those studios using True HD turn off dialnorm. The only other difference between the two is the method of lossless encoding: DTS has a proprietary method, while Dolby bought Meridian and therefore uses MLP.
RE: Lower volume on a True HD mix, all lossless mixes are mixed substantially lower in volume than DVD tracks, in order to exploit the full dynamic range of lossless. If you find True HD tracks too quiet, you can adjust your dynamic range compression level (DRC), or you can dial in a volume offset according to source. Most receivers have one or the other, or both as features (My Onkyo HT-RC460, for example).
I use BDInfo sometimes when taking screencaps, i have seen dial norm on some Dolby soundtracks on blu ray and it has certainly been on, as for dynamic range, unfortunately too many soundtracks on blu ray are being altered and the overall dynamic range lowered, the difference between low and high sounds remain the same so that's something but reference volume is not the same as you get at the cinema, it varies on which movies they do this to but it certainly happens, the film mixer who resides over at AVS forums talked about it a few years back.
Dynamic range is good though and whenever i read a reviewer stating that dialogue is low and action scenes are too loud i am pleased because i know the dynamic range is intact and that the movie will sound fabulous when i listen to it at the proper volume levels. ( even if lowered from the cinema ) Dynamic range compression should never be on unless listening late at night and you are worried about upsetting the neighbours. Calibrate your audio, set it all up and leave alone, everything should then sound good, the only problem is if you like to listen at -30 ( as one example ) and your hearing is starting to go a little ( as mine is ) then yes you may well run into trouble hearing speech in some films.
I listen at -10, all films, no changes are made, you shouldn't be making changes, the neighbours don't like me.
Edited by FoxyMulder, September 03 2013 - 02:20 PM.