Guess it's time to revive bendermac's dated request for an authentic mix as I'm currently sitting there with two HD versions of Panic Room (some obscure web-dl in cinemascope and an Amazon open matte one), intending to sync that to the "least fiddled around with" original 5.1 mix.
The usual "decentralized backups" come along with a bunch of tracks, sometimes AC3, sometimes E-AC3 whereas the latter ones suggests some streaming web source as since the death of HD-DVD, E-AC3 is pretty rare on any physical media these days.
Independently of the concrete format which is secondary, the mixes are clearly different as some analysis of for example the respective center channel shows (decoded with eac3to, libav codec, hence dialog normalization removal and no DRC of course):
The one in the middle for instance is taken from some "DVD rip" coming in AC3 shape and in sync with a "25p" picture, so it could originate from a PAL DVD which is also supported by the fact that the nominal bitrate is 448 kbps which is at least possible on DVD. Since the quiet sections have a lower level and the peaks a higher one compared to the
others first, by definition, the (macro) dynamic range is significantly higher. I guess at least the
3rd 1st one went through some "dynamic range reduction", just as the track which comes along with the Amazon open matte version of "Inside Man" by the way.
Update and correction: I'm sorry, my mistake/confusion - actually, only the first track significantly differs, track 2 and 3 look and sound pretty much the same once normalized to the same level, so maybe number 3 is actually sourced from a NTSC DVD (it comes along in AC3 @ 384 kbps). This would match the review which was referenced here as the overall mix level about 4.5dB lower (which of course can easily solved by using the volume (actually gain) control during playback.
I assume that they used the same source for the PAL and NTSC DVDs then, the major difference being that the PAL DVD runs faster with pitch correction (so bringing that one back to 24/1.001fps by eac3to sounds deeper than all the others).
As far as I can tell on a quick check, the pitch of the 25p AC3 equals the 23.976 fps AC3s, probably, the pitch has been adjusted to match the NTSC speed on that particular DVD so technically, it's already a "mangled around with" case although the loss most likely will be minor apart from the wrong effective speed of course.
The other tracks which come along with those HD versions are encoded at 640 kbps, a bitrate, no official DVD source offered, so it's most probably some reencode here.
Taking the principle problem of knowing which one is "toned down" and which one "beefed up" aside, what would still be nice for comparison is - if not the "holy grail" - the Cinema DTS - then at least some unaltered AC3 and/or DTS track from a (US) NTSC DVD.