Quote from DVDTown.com review of Iron Man BD:
"I compared several passages to the regular Dolby Digital 5.1 track on the standard-def version of the movie, and, sure enough, the SD disc had the punchier sound. I also compared the TrueHD and regular Dolby Digital tracks (for French and Spanish) on the Blu-ray disc itself and found the TrueHD sounding a bit lower in output. But even when level-matched, the TrueHD sounded slightly wimpier to me. I can't explain why it's happening, nor can I tell you which version is more true to the movie's original soundtrack. I can only describe what I hear, and what I hear makes me favor the regular Dolby Digital, at least in regard to its seemingly wider, more-potent dynamics.
Audio addendum: Not trusting my ears, I used a sound-level meter to test the difference in one of the softest and loudest passages on the disc. I chose scene fourteen, when Pepper is speaking to Tony on the telephone, and as the reference passage I chose the line "Odadiah, he's gone insane," which I set for 70 db. Then I measured the appearance of the villain, crashing very loudly through the basement roof. In TrueHD, the difference in loudness was +24 db, the villain producing a noise level of 94 db (compared to the 70 db for Pepper's line). Then I measured the same line from Pepper and the same crashing through the basement roof in regular Dolby Digital from the standard-definition disc. The loudness difference this time in regular Dolby Digital was +28 db, about four decibels greater in regular DD."
