Encode for DVD and keep Pro Logic?

[Michelle]

It seems to me that the best way to encode a stereo PCM file is MPEG-1 Layer2 for keeping the Pro Logic info. But a DVD requires that one audio track must have Dolby Digital or PCM Audio. With DD you lose the Pro Logic info and PCm just takes up too much space. So it seems that the only way to keep Pro Logic is to have 2 audio tracks DD and MPEG-1 Layer2. But then of course my authoring program, DVD Lab, only supports one audio track.

Is my understanding of the situation correct?

[Baldrick]

Are you sure that you lose the prologic if you convert to dolby digital stereo only? no dolby digital 5.1. I don't think so...but I know nothing about audio...

[mkelley]

Did you see this thread?

https://www.videohelp.com/forum/viewtopic.php?t=169411

Explains some things about Pro Logic (and perhaps makes Michelle's questions moot).

[Michelle]

I read that thread yesterday. If there's something in there that makes my question moot then I'm missing it.

[flaninacupboard]

well the point is that a pro logic signal can be in -any- stereo sounds. casette tape, video tape, CD, hell even vinyl could have a pro logic soundtrack! all you need to do is encode to dolby digital 2.0, and if your encoder supports it (the one bundled with scenarist does, i assume other do to) set the "pro logic" flag as "on".
now when you play the track back on your dolby digital amp it will automatically set it self to "Dolby Digital - Pro Logic" or "Dolby Digital - Pro logic II - Movie" if you have pro logic II.
if your encoder doesn't have the option to set the dolby surround flag, then you will have to switch the amp to pro logic mode yourself, but the effect will be identical.

[mkelley]

Well, unless I'm missing something what it tells me about Pro Logic is that the encoder takes the two channel source and "creates" four channels from it. Which means there is nothing inherent in that two channel source to begin with.

So you wouldn't be losing anything in DVDLab -- IOW, there IS no such thing as a Pro Logic coded stream, only a Pro Logic decoded stream.

[flaninacupboard]

in a sense there is no such thing as a pro logic encoded stream. there is however such a thing as a dolby surround encoded track. i use the word track to emphasize the point it's not a stream in the sense of mpeg, and it doesn't even have to be digital. dolby surround info can be in -any- stereo source. it's all to do with the way the stereo soundtrack is mixed, noting to do with bitrates or filesizes or any of that malarkey.

dolby surround is encoded more or less like this.
you have a left channel, a right channel, a centre channel and a rear channel. you then clip the centre and rear channels, reduce their volume, add the centre to the left, add an inverted centre to the right, then add the rear to the left + centre and an inverted rear to the right + centre. you only have two channels, but it's possible to reverse the adding and inverting process using a pro logic decoder. you can then put this stereo soundtrack on a CD, or a VHS tape, or a laserdisc, or a DVD or a VCD, or even play it on the radio or show it on TV. a pro logic decoder will pull out the centre and rear info and amplify accordingly. it's actually a very clever system, considering it's like 3 decades old!!

[Michelle]

all you need to do is encode to dolby digital 2.0, and if your encoder supports it (the one bundled with scenarist does, i assume other do to) set the "pro logic" flag as "on".

I guess that's the key. I'm using the encoder in Vegas Video. There is a Custom button but unlike the other encoders this one isn't available to change settings.

[flaninacupboard]

fair enough, the amp won't switch to the right mode itself. if you switch the amp yourself to pro logic mode you will find the surround sound works perfectly. go try it!!

[Michelle]

Well, unless I'm missing something what it tells me about Pro Logic is that the encoder takes the two channel source and "creates" four channels from it. Which means there is nothing inherent in that two channel source to begin with.

So you wouldn't be losing anything in DVDLab -- IOW, there IS no such thing as a Pro Logic coded stream, only a Pro Logic decoded stream.

This would be the case if I kept it in PCM format. But I want to compress it. If I compress to AC3 then I can't access the Pro Logic decoder on the receiver.

[Michelle]

fair enough, the amp won't switch to the right mode itself. if you switch the amp yourself to pro logic mode you will find the surround sound works perfectly. go try it!!

I already have tried it. It won't switch.

[TOMMO]

If you have Vegas 4 you can encode your home movies to either 2 channel or 5.1 surround AC3. However, to enable this function you need to have DVD Architect installed.

[Michelle]

If you have Vegas 4 you can encode your home movies to either 2 channel or 5.1 surround AC3. However, to enable this function you need to have DVD Architect installed.

I have DVD Architect but it wasn't installed. I installed it and now the Custom button works. I tried all the audio coding modes and the only one that wasn't invalid is 2/0. Then I tried turning on 'Dolby Surround encoded' and it accepted that. It now plays in DD 3/1. This is excellent. Thanks a lot for your help guys!

[TOMMO]

In Vegas, If you go FILE > Preferences > AUDIO tab, you can set vehas up for Dolby 5.1.

If you go to OPTIONS> Audio > you can set the channels etc.

[flaninacupboard]

I already have tried it. It won't switch.

That's kinda odd....... Mine will do it no problem!
Are you sure your DVD player is set up to output the sound correctly? i.e. in DD instead of PCM. but even so it should be switchable.... weird!
Actually, if it -won't- let you switch to pro logic with 2.0 DD then you could use the stereo analouge out of your DVD player, and that will -definitely- be switchable to pro logic.
but if you fixed it by enabling the surround encoded flag, then that's fine too. just thought i'd throw in your other option

[Michelle]

If you go to OPTIONS> Audio > you can set the channels etc.

I don't see anything under Options for setting channels. But Iwas able to create a 5.1 file by changing the Audio properties for the project. This is very interesting. Thanks!

[Michelle]

In this situation (converting stereo to DD) is there any advantage to 5.1 over 2/0 with the Surround flag set? Doesn't the 5.1 just create a much larger file with the same audio information?

[flaninacupboard]

In this situation (converting stereo to DD) is there any advantage to 5.1 over 2/0 with the Surround flag set?

No. only if you're intending to use a DD amp with no pro logic mode. as far as i am aware they do not exist.

Doesn't the 5.1 just create a much larger file with the same audio information?

Yes. you should get much better results with 2.0 and the surround flag