How to adjust audio level in AC3?

[mtbsoft]

Not sure where to ask this one so...

I'm encoding our DVD collection for playback in both the theatre (projector) and the family room using WD TV Live media players.

Since the majority of the stuff is for the kids, I'm quite happy just to use the AC3 audio channel with AC3 Passthru - it gives a perfectly good result (to my ear), even on the 7.2 setup in the theatre. I'm encoding to H.264 in an m4v container using "tweaked" versions of the animation preset, on a W7-32 box, only adding one audio soundtrack, ripped using DVDFab 6.2.

However, on a couple of disks (so far), I've found that the audio seems rather low in volume, markedly so, in comparison to the majority of the rips/encodes and I'm wondering...

1) if anyone might be able to suggest a reason why the audio might be so much lower (the source DVD doesn't seem to play lower than the other DVDs). I'm assuming it is a WD TV Live issue but curious why the same ripping and encoding method (particularly with passthru) should result in so varied a result.
2) more importantly, is there a tool out there (either win or linux) that I can use to easily alter (increase) the volume level on the audio track. It would be nice if I could use it to "normalise" a few of the louder ones down a bit, too.

Any suggestions gratefully considered.

[mkelley]

I have three WD Live units and have ripped tons of DVDs (and blu rays) and never noticed this -- it's very odd to say the least. I also passthrough either the AC3 or DTS tracks and I never adjust the volume on our playback devices (or if so, very very slightly).

You can use ffmpeg to change the volume on an AC3 track easily. Not sure why you'd have to do it, but there you are <g>.