Film-Tech Forum ARCHIVE: Home Cinema: Pro-logic II and Dolby Digital

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Posted by Michael Brown (Member # 890) on 09-09-2002, 06:20 PM:

This is not for me but a friend.

If buying a new home cinema (DVD) set up, would it be best to equip for Dolby Pro-logic II and Dolby Digital?

I.e Are there Discs produced that carry a Pro-logic II soundtrack without also having a Dolby Digital track?

Posted by Steve Kraus (Member # 476) on 09-09-2002, 06:27 PM:

I don't follow home theatre developments much but I would wager any Dolby Digital-equipped receiver is going to also be able to decode 2 channel analog "Pro Logic" as well so it's not like you would be giving up the one to get the other.

Posted by Michael Brown (Member # 890) on 09-09-2002, 07:45 PM:

I mean is it worth equiping for pro-logic II as well as Digital.

Are there DVD's that carry prp-logic II tracks without Digital tracks?

Posted by Joe Redifer (Member # 3) on 09-09-2002, 08:57 PM:

I've never seen any movies or DVDs that have Pro-Logic II. I think that videogames are the only media that actually use it.

Posted by Mike Schindler (Member # 1309) on 09-09-2002, 09:25 PM:

I have heard of video games that are labeled as Pro-Logic II, but not any movies. I just bought a receiver which has Pro-Logic II. It wasn't a feature that I really cared about, but I played around with it a bit. It kind of works sometimes. I listened to a couple pieces of music which were listed on the Dolby website, and it sounded cool, but I'd personally feel guilty about listening to something in a way which was not intended.

The only movie I've listened to is THE EMPIRE STRIKES BACK special edition LD. Most of the time, it sounded almost identical to listening to it in Pro-Logic, but there were a couple times where you could hear an effect on only one rear channel, and it actually felt like it was meant to be there.

I haven't heard anything which was designed to be played in Pro-Logic II, but the things which I have listened to have sounded "better" than when played in Pro-Logic. However, this thing also has DTS NEO 6, which can separate a 2 track source into 6.1 channels. I listened to the music in both of these formats, and it sounded better in Pro-Logic II. I haven't listened to a movie all the way through in both, but my friend and I have decided to watch the new TRANSFORMERS and HE-MAN cartoons in DTS NEO 6 (just because we can), and they have both sounded much better than the films that I have watched in Pro-Logic II.

I don't know if any of this has helped at all. I wouldn't make your decision based on my opinion, especially since I haven't really bothered doing any sort of comparisons or anything like that. But if I were in your friend's position (which I was, about a month ago), I would not pay extra money for Pro-Logic II. Especially if most of the things which are being watched are in 5.1. There's really no point. That being said, it is kind of cool (even though it's iffy from an artistic standpoint). But if he is interested, he should also definitely look into DTS NEO 6.

But here's my question. Now that Pro-Logic II exists, are people mixing TV shows for this format? This is very important to me since THE SOPRANOS starts in a mere 6 days. Should it be heard in Pro-Logic or Pro-Logic II?

Posted by Mark Lensenmayer (Member # 134) on 09-09-2002, 10:34 PM:

Here is what I understand about Dolby Digital, Pro Logic II and DVD's.

All DVD's should have a Dolby Digital track. This is required by the standard. DTS, PCM, MPEG-1, MPEG-2and (a not yet developed) SDDS track could be added BUT the Dolby Digital track must be there. (My source is DVD Demystified by Jim Taylor.)

Dolby Digital tracks can have from "1 to 5 channels of discrete audio". A sub-woofer channel is also available. A sixth channel can be derived from RS and LS.

Pro Logic can be used on a two-channel Dolby Digital signal to create 4-channels (L-C-R-S). Pro Logic II is a second generation decoder that claims to do a better job, even to some separation in the rear channels. So, in my opinion, Pro Logic II should be used for 2-channel decoding, but it really is at the discretion of the user. Sometimes there is a flag on the data that will automatically activate Pro-Logic II on a 2-channel signal. It's similar to the flag that activates Dolby Surround-EX. Not all DVD's use this.

Pro Logic II has 2 modes, a Movie mode and a Music Mode. The Music mode has some adjustable parameters.

I run my standard 2-channel TV audio through Pro-Logic II and it does a pretty nice job.

The Dolby Web site has some good information on Pro-Logic II. I found this to be very helpful:
http://www.dolby.com/ht/co.br.0107.PLIIListenersGuide.html

CORRECTION AND ADDITION: Above I stated that a Dolby Digital track is required. The CORRECT statement should be that on a NTSC DVD, either a Dolby Digital OR PCM track MUST be available.

Some more info on the missing SDDS system. "SDDS is an optional multichannel (5.1 or 7.1) digital audio format, compressed from PCM at 48 kHz. The data rate can go up to 1280 kbps. (DTS has a max of 1536 kbps)."

My source does not define the format of the 7.1, whether is is a 5 front, 2 surround model like SDDS-8 (likely, in my opinion), or the new 7.1 proposed format with 2 rear surround speakers, effectly a LR and a RR.

Posted by Steve Kraus (Member # 476) on 09-09-2002, 11:56 PM:

Very interesting. Is this something that is going to migrate from home theatre to cinema use?

Posted by Joe Redifer (Member # 3) on 09-10-2002, 01:11 AM:

Vieogames in Pro Logic II have sounded very good, with extremely discrete surrounds. Not quite as good as Dolby Digital or DTS, but very impressive considering the source.

What I really want to know is exactly how Pro Logic II derives the surround information and separates them. How is it encoded? Pro Logic 1 is normal stereo, with in-phase info shoveled into the center channel and out-of-phase info tossed into the surround. So if I want to encode in Pro Logic, I just make sure my center channel sound is in phase and my surround channel is 180º out of phase and it works every time.

Posted by Michael Schaffer (Member # 1204) on 09-10-2002, 12:10 PM:

Pro Logic II compares the surround signal derived from Lt and Rt to the L and R channels after the matrix decoding. If there are correlations between the decoded surround channel and either front channels, it puts the signal on the surround channel on the same side. That is a vastly simplified explanation of course, but I think only Dolby engineers could explain the process in all details.
Most of the new equipment comes with Pro Logic II anyway, so you don`t have to worry too much about the choice. It`s also fully downward-compatible.
It is very unlikely that Pro Logic II will find its way into theaters, since it only enhances analogue playback when so many theaters already have digital processors with discrete surround channels.
Speaking of DVD equipment and all, I am planning to buy a home cinema set in the near future. Any recommendations? I have an affinity to Harman/Kardon equipment and am planning to buy a mid-range receiver from their product list (2500 or 3500). Or would anybody recommend me another processor, sorry receiver?
Michael