there's still a puzzle as to the dolby digital encoding

Hi, I have read nearly all the tech docs possible before posting these words. The puzzle is still about the lower sound level of the dolby digital encoded audio. I think I do know all the meanings of the settings of the encoder. I just made such a test. I encoded a video and an audio file (48khz, 16bit,stereo) to DVD-MPG file with audio settings like this: encode in digital stereo mode, dialog normalize = -31db, any filter is off ,dc offset remove is off (for I want to get rid of any causes which can effect the sound level). as you know, the most important setting is dialog normalize. then I think the audio decoder won't attenuat the level of the decoded audio, since the setting is -31 db. but to my surprise, the playback audio is very easily to be heard lower than the origional audio file. I didn't use hardware players, all the software players which support metadata have this problem. I record the playback audio ( in digital ways) and compare with the origional file, it's very clear that the playback audio is lowered by about 6 dbs!!! why can this happen? as far as I know, no doc has explain this. anyone can solve this puzzle? thanks.

What did you use to play the sound? PowerDVD, WinDVD, AC3filter, ffdshow? AC3filter has about 4 to 5dB lower levels than most decoders for AC3 while not for DTS. Cheers.

well, I often used window media player, media player classic before. after I change to windvd 7, there's no such sound level problem. It seems the problem is due to the old ac3 decoder, right? but why the old ac3 decoder behaves like that? to protect the decoded audio overload the sound card circuit? and I have notice another thing. after installing windvd7, all the software players don't have the lower level problem anymore. maybe windvd7 has replaced the ac3 decoder in the OS which all other players will call on?