Pro. And it looks like it's only recompressing the 2.0 file, not the 5.1. Both were created from the same Vegas project, and both AC-3 files are the same size.

sean,
did you check your File / Properties / Disc Properties and audio defaults?

Yes, everything looks right. Both AC-3 files are 448. I don't think it's a space issue because it wants to recompress the 2.0 file even if I select an 8.5 DL disk. I don't do much authoring, so maybe I'm going about the whole thing wrong. I'm trying to give a client a disc with both 5.1 and 2.0 mixes. I've created a menu for each, each referencing the same video file. The 5.1 mix is on track one and the 2.0 mix is on track 2, with the Action in the Button properties specifying which audio track to play. Does this sound right?

In some cases, you can go into properties and tell it not to recompress. It may be trying to make this track match the default.

Dave T2

I noticed when playing back the burned DVD in my home theater that the 2.0 audio had been recompressed at 192. I went back to Vegas and rendered a new 2.0 track at 192, though Vegas displayed a warning that 448 was recommended. DVDA still wants to recompress the 2.0 track. Just in case DVDA might have been duplicating files, I completely removed the second button, leaving the alternate 2.0 audio but without its own menu option. No change. It still insists on recompressing. Totally confused.

Go to Optimize Disc (under file). Select the Video and look at the AUDIO column. Recompress settings is probably set to default, so it is going to do what the default properties are set for. change that to what you want.

Dave T2

It's not necessary to include a separate stereo AC3 file in your DVD if it is the same audio program as the 5.1.

There is a mixdown flag set that automatically tells your player to deliver stereo if you choose it, as well as through analog outputs. The result is better than anything I can mix manually, and I've been doing this for decades.

I'm thinking you are absolutely right, because in my torture-tests in my home theater, I actually like the sound of the 5.1 mix when played back in straight stereo better than the separate 2.0 mix.

Do you opt for the Lt/Rt preference or the Lo/Ro preference? Or does it really matter?

For pure stereo (only), Lo/Ro is "technically" more accurate.
Lt/Rt introduces a phase shift so that the stereo can be upmixed for Pro Logic (matrix surround) decoding say, by an analog receiver.

To be quite honest, I have a hard time hearing any difference between the two, even with pristine classical music. Lt/Rt I'm sure is the default for the AC3 downmix flag.

These tests I ran a few years back on the AC3 Pro encoder may be of some interest.
Several here have created their own templates using these suggestions as a starting point:I've run some exhaustive tests with calibration test tones and done extensive reading of the Dolby metadata specs, and in reference to your question about the most accurate reproduction with the AC-3 Pro Encoder, I am prepared to make the following recommendations with notes:

Thanks, I had actually printed those out awhile back from another thread. Just to confirm one thing: when creating a stereo AC-3 file from a 5.1 setup in Vegas (assuming one still wants to do so), I found it necessary to select the 3/1 (L-C-R-Ls) option or Vegas would ignore everything but the front surrounds in the resulting mix. Is that to be expected? And is there any need to specify Dolby Surround or a downmix preference when creating a 2.0 file in the 3/1 configuration?

Taking your questions in reverse order,
2) Again, this would only come into play if you needed to render a Pro Logic compatible stereo file.
1) It has been so long since I actually encoded a stereo file from a surround project, that I'm not certain, but I assume you are correct; only the channels set in the dropdown would be mixed into the outptut.

Sorry to belabor this (I think I hijacked my own thread), but wouldn't it be superfluous to check the Lt/Rt preference for a Dolby 2.0 file? Doesn't downmixing a 5.1 project to 2.0 converge all the center and surround information? My guess is that playing back a Lo/Ro mix through a PLII decoder would yield pretty much the same results as a downmixed 5.1 with the Lt/Rt preference selected. As I understand it (which isn't saying much) the Lt/Rt flag will only affect how a 5.1 AC-3 track will play back through a Pro Logic decoder. True?

That's not my understanding, but I haven't specifically tested. Why don't you do so, and we'll be interested to see the results.