Originally Posted by Drew Eckhardt
From dialog to a roar.
The Dolby meta-data actually encodes dialog level relative to 0dBFS (maximum digital signal) with a 31dB maximum.
Not exactly (although my description may describe what you meant...)
Included in the Dolby Digital metadata is a term that indicates how loud dialogue is in the program. The measurement, like most digital measurements, is in dB referenced to full scale digital (dBFS.) Most films have dialogue that measures around -27 dBFS. This is, perhaps surprisingly, is the same for Batman or any other film, even a documentary. This consistency results from movie sound mixing facilities world-wide being calibrated to the same loudness. Film mixers don't touch the volume control. They adjust their mix.
Not everything is mixed under these conditions, unfortunately, so the indicated loudness might be different than -27. That value could be as low as -31, but usually doesn't go above -23 or so.
This is normal spoken dialogue, so shouts will be louder and whispers will be quieter, but over the course of a film these will average out. This is an attempt to measure how loud it sounds to the listener, so the measurement is A-weighted.
So, there could be as much as 27 dB difference between dialogue and the loudest sound in a film. This is dependent on the type of film it is (action, drama, comedy, etc.) There is about 100 dB range between the loudest and quietest sounds possible in the Dolby Digital system, but most films (or even real life) don't get even close to that lower level.