HeadAC3e, LFE, and Re-Encoding

[triad3204]

Okay, here's what I'm doing:

(1) I'm taking a DD5.1 AC-3 file and using HeadAC3e to rip out 5 mono WAV files, one for each track (Center, Left, Right, Rear Left, Rear Right).

(2) I'm using SoundForge to edit each track. These are generally not major changes (I'm just smoothing over hard edits done in an MPEG editor before the AC-3 file is demuxed). Most importantly, the length of the file is unchanged because it still needs to synch back up to the original video source.

(3) I'm using Sony Vegas to re-encode the tracks to DD5.1 AC-3.

This seems to be working OK, but I'm wondering about the original LFE track. I'm getting at least some LFE action after the re-encode back to DD5.1, but I'm wondering if I'm losing audio information by failing to decode the LFE and then re-encode it back into the new DD5.1.

Am I?

And if I am, what would be the best way to get that information back into my final version?

Thanks.

Justin Bacon

[ursamtl]

Depending on how the original source 5.1 mix was done, you may be missing all audio information before the crossover frequency used by the person doing the mixing. Try ripping out the LFE wave and then open it in SF to see what's there. If there's any audio there, it's best to include it in the re-encode, but then check your settings in Vegas. If you're getting LFE info when re-encoding but you haven't included the original LFE, then chances are Vegas is splitting the lows at some crossover frequency and then routing everything below to the LFE channel. I've never used Vegas so I can't say what to check, but surely there's a way to encode an existing wave for LFE without generating extra info.