Layer II audio -> DD, do the surround stuff get lost ???

[jcabello]

After some thinking ( and some DVDs burned this way ) I was wondering that if I convert the Layer II audio to Dolby Digital 2.0 the surround encoding will be lost or it is kept during this process. I've done this because it is known that the DD encoding is better compared to the layer II audio.

Wikipedia offers some hope stating that:

"Although Dolby Surround was introduced as an analog format, all Dolby Digital decoders incorporate a digitally implemented Dolby Surround Pro Logic decoder for digital stereo signals that carry matrix-encoded Dolby Surround."

http://en.wikipedia.org/wiki/Dolby_Pro_Logic

So the question to the experts remain: If I have a movie that have Dolby Sound it is best to keep the Layer II audio or convert it to DD ???

[captain_video]

It really doesn't make any difference unless your DVD player doesn't like mpeg II audio. Going from mpeg II to DD 2.0 probably won't sound any different because it's basically a stereo signal with no surround effects. You may be able to get some pseudo-surround effects, depending on the type of decoder setup you have but it would probably be on the order of Dolby Surround but definitely nothing like DD 5.1.

[jcabello]

First of all thanks for your prompt response. All that you ( captain video ) state is true, but the question that I have is that if a have a movie that I know have Dolby Surround in layer II and I convert it to Dolby Digital 2.0, do I lose the encrypted information in the transcoding/conversion ?

I don't have anything to test because my reciever just states if the stream is in Dolby Digital ( doesn't matter if its 2.0 or 5.1 ).

The reason that I want to know is because I burned to DVD some 40 movies using this technique and I want to know if it is the right way to do it or do I have to Tivo'ed them again to get the best quality.

[cheer]

OK, so what we're really talking about here is Dolby Pro-Logic (or Pro-Logic II), and the question you're asking is if you convert the audio to DD2.0, will it still retain the Pro-Logic II information?

I've done some experimenting with this, and on my setup the answer is "Yes and no."

Pro-Logic (I/II) is, as you quoted, matrixed into the analog audio. So long as that audio is never filtered out, the PLI/II information is absolutely there. For a long time I used to Divx-up DVD rips this way, before I cooked up a way to play my Divx files with DD5.1 or DTS.

So as near as I am able to determine, that information is still present in the DD2.0-encoded audio.

However.

My receiver, upon receiving a digital audio stream, automatically grabs that stream and plays the digital output that it delivers. It is not possible to tell it to ignore the digital stream and treat it as Dolby Pro-Logic -- quite rightly, since the only connection between my DVD player and the box is a digital one. Since it sees the stream as DD2.0, that's how it's played -- and the back speakers (and center channel) aren't even on.

If I burn a DVD with just the M2A audio, however, it actually comes to my receiver as PCM 48, and again the back speakers are off.

The bottom line (at least on my receiver) seems to be that if a digital audio signal is received, it's going to play that audio as is and not bother with any analog surround processing. YMMV and all that.

In any case I wouldn't bother re-encoding the audio; I don't think it buys you anything.

[mrdizzy]

As far as I understand it if you have a 2-channel soundtrack on a DVD it can be stored as at least:
* PCM
* Mpeg 1 layer 2
* Mpeg 2
* DD 2.0 (flagged as "stereo")
* DD 2.0 (flagged as "this 2-channel soundtrack contains Dolby Surround information") [this is different to: DD3.1]

In the last case the amp should auto-switch into pro-logic mode, if you are using SP/DIF etc. Many of my commercial DVDs do this for trailers/clips etc, on DD2.0 soundtracks, so it is definitely possible.

I don't think all of the surround information gets lost (although some must); the real question is how to set the flags to indicate that the surround information is present on the finished DVD. It's annoying to have to switch manually sometimes.

[jcabello]

Well, after so much reading and experimentig with the audio format this is my experience.

The movies that I am sure that have Dolby Surround encoding and then convert them to Dolby Digital 2.0 play well on my setup ( Xbox XBMC, Kenwood reciever ) and it gets the Dolby Digital signal 2.0 and rightfully so plays just the front speakers.

My reciever was able to "downmix" the DD 2.0 to Dolby Surround and I was able to get the 5 speakers to work. The overall audio quality is between good and very good.

I wasn't able to test the source and the "project" because my reciever on ly have one optical input and I have to change the cable every time I want to hear each source. I ordered an optical switch and I will be able to make more tests.

[mrdizzy]

Well, after so much reading and experimentig with the audio format this is my experience.

The movies that I am sure that have Dolby Surround encoding and then convert them to Dolby Digital 2.0 play well on my setup ( Xbox XBMC, Kenwood reciever ) and it gets the Dolby Digital signal 2.0 and rightfully so plays just the front speakers.

My reciever was able to "downmix" the DD 2.0 to Dolby Surround and I was able to get the 5 speakers to work. The overall audio quality is between good and very good.

Yep. Because it can be
* DD 2.0 (flagged as "stereo")
or
* DD 2.0 (flagged as "this 2-channel soundtrack contains Dolby Surround information")

There should be a way of setting the flags on the DVD so that the receiver will automatically switch into Dolby Surround mode, without you having to switch manually. (I regret I haven't had time to look into this as much as I want to)

I wasn't able to test the source and the "project" because my reciever on ly have one optical input and I have to change the cable every time I want to hear each source. I ordered an optical switch and I will be able to make more tests.

Cool stuff!