This is a common occurrence for converting ac3 to MP3 for audio as there is an approximate 8db difference in level between the two formats. VLC has 6db of gain in the volume control where as WMP has 0db of gain. So as an end result the volume must be turned up on your audio card to a more appropriate level. Or you will need to use gain compensation in a third party program and transcode with a different program.
Many thanks for your reply, DJ!
But VLC seems can't solve this problem neither.
I read some posts from AC3filter Web site, and see they have mentioned the use of DRC.
Can the use of DRC solve the problem of low audio output, DJ?
I can feel that you have much experience on video conversions.