recompressing audio - can't stop it

Doug_Marshall wrote on 5/19/2006, 11:59 PM
I'm doing a really simple DVD - just a surround ac3 sound file prepared in Vegas and a single slide so the TV won't be blank. It basically just plays when you pop it in the player.

The ac3 file was prepared using the surround template in Vegas (with audio compression turned off). DVDA3 seems determined to recompress the file and wrecks it in the process by compressing the music. Vegas's ac3 file should be compliant. What could be wrong?

Comments

Chienworks wrote on 5/20/2006, 4:14 AM
I'm a little confused. What do you mean by "with audio compression turned off"? AC3 is always compressed. If you want no compression then you would use WAV.
Doug_Marshall wrote on 5/20/2006, 9:26 AM
Sorry, poor choice of words. What I meant was that when I encoded to ac3 in Vegas I turned off dynamic range compression in the encoder. Then, when I prepared the project in DVDA, it insisted on recompressing the file although it is already allegedly DVDA compliant. Audio wrecked.
bStro wrote on 5/20/2006, 10:26 AM
Locate your AC3 file in DVDA's explorer window, right-click and choose Properties, copy / paste that text into a post so we can see what's what.

In addition, please confirm that DVDA is attemptiong to recompress the audio and not just the video. Sorry if this is an insulting request, but it has to be made. In my experience, it's pretty rare for DVDA to want to recompress an AC3 file.

Rob
Doug_Marshall wrote on 5/20/2006, 12:06 PM
Not insulting at all! You put me on track to solve the problem. A few versions ago, this little project worked smoothly so I compared properties of an older ac3 with the current one. The audio for the old one said 5.1 surround and the new one said 3/2 multi-channel. I had changed the checkbox in the encoder to disable the LFE, not anticipating that this would cause a problem. Re-enabling LFE resolved it.

My confusion arose because in my Vegas project I disabled the LFE in the properties, under advice from a mastering house I've worked with. They said not to create a discrete LFE channel for classical music - just let the end user's decoder do it - to prevent the bass from becoming too heavy. I assumed, to be consistent, that I should also disable it in the ac3 encoder. Wrong!!!
MarkWWW wrote on 5/21/2006, 4:02 AM
Ah, yes, DVDA seems to be a bit fussy about AC3s. It doesn't seem to like anything other than 2.0 or 5.1, even if they are created by the Dolby Digital encoder and so should be perfectly according to the spec.

As you've found, DVDA doesn't like 5.0 files, and I have also found that it doesn't like 1.0 files either. I was attempting to use some of these for commentary tracks (to save a bit more space) but found that they weren't accepted by DVDA.

(I later discovered that although 1.0 is a perfectly legal format for audio tracks on a DVD, some players just won't play them so it wasn't such a good idea anyway. I've got a couple of commercial DVDs that use 1.0 tracks and while all my software players can replay them, neilther of my hardware DVD players will - you just get silence.)

Mark