sb4101 said:
What I am looking for is a setting (or something) that will allow me to listen to a DVD (or TV, or CD) such that ALL audio playback is at the same volume level, regardless of whether it is a whisper or an explosion.
It is next to impossible to achieve what you want although there are some features that can help a little.
Dynamic Compression as mentioned above will reduce the peaks and make the average level higher so there isn't a drastic difference between dialog and explosions, but it only works on Dolby Digital.
Some Yamaha receivers I've heard have a volume leveling feature that is similar to what Onkyo calls 'IntelliVolume'. It simply allows you to set an offset between different inputs. So, IF your CD input always seems to be about 10 dB louder than the DVD input, you can set the offset for CD to -10 dB. That doesn't help all that much because every CD has a different level as well as every DVD, so one offset will not likely achieve the goal of making all media from each input sound about the same level. Just think about a CD mastered in the '80s vs one mastered in the '90s. An offset of -10 dB might reduce the level of the hotter '90s CD so it matches more closely to the DVD input, but as soon as you put in the softer '80s CD and it is reduced 10 dB it will now be too quiet and you have to reach for the volume control anyway.
The ear responds to the average level and volume leveling is an attempt at making the average level similar across sources. It is not a cure-all because there is more to 'perceived loudness' than the average level. If you take two songs, say one hard rock and one soft rock and adjust them so that their average level is similar, the hard rock will still be perceived to be louder simply due to the type of music. iTunes does just that - it calculates an offset across your entire collection. Look at the ID3 tag of a file that has been processed by iTunes and you will see a tag called 'engiTunNORM' - that tag stores the 'normalization (NORM)' volume offset. Adjusting average levels will get you close, but not perfect.
You would need a compressor that would adjust levels on the fly to a value you specify, and you will never find such a feature on a receiver. Until there are standards for broadcast and recording levels this is a problem that will persist.