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Newbie Help: Surround Sound simulation from 2 channel Stereo

post #1 of 6
Thread Starter 
Hello, I am a newbie in the surround sound arena and I have a very basic question. I have been reading that in surround sound technologies such a Pro Logic, the decoder can take a two channel Stereo feed and output it as a simulated 5.1 surround environment. I thought this was possible only if the stereo feed had embedded the additional channel info. In other words, I can understand how Prologic (or other similar technologies) can extract from the original stereo feed the additional channel info "if" this information was present and available........if this information was not present on the original stereo feed how would Prologic know what goes to which channel? In other words, if I am hearing a Music CD that is standard 2 channel only, can something like prologic simulate that into 5.1 surround?

-Andy

San Francisco
post #2 of 6
First off, Prologic is very old and obsolete today. It has been replaced by Dolby PL II for 5.1 and Dolby PL IIx for 6.1 and 7.1 speaker setups. These newer processing algorithms work much, much better than the old Prologic.

The 2 channel material does NOT need to be encoded. PL II and PL IIx can simply work with a stereo source. I'm not even going to try to explain how it's done since I don't know most of the details, but certainly using the stereo information such as common (mono) content, the phantom sound stage created by the stereo signal, the phasing of L/R content etc..., you can imaging that it's possible to do a good job with today's powerful DSPs.

Note also, that the "Music" (vs Movie) flavour of Dolby PL II and IIx allows you to customize the width and depth of the surround sound field for 2 channel recordings.

Ed
post #3 of 6
I believe up to five channels can now be encoded using PLII for transmission over a stereo path. That should provide better surround than you get with a regular stereo source and matrix processing applied by PLII decoding. PLII encoding is used in some analog TV transmission and video games.
post #4 of 6
Thread Starter 
Thanks Ekb and Bislander for the the info. Now I understand better.

BIslander, when you say 5 channels can be encoded in a stereo stream..........you are referring to the source (the film maker, the DVD, etc) and not my PL II decoder in my receiver that will decode these 5 channels correct?

-Andy
post #5 of 6
Quote:
Originally Posted by Andyt123 View Post

BIslander, when you say 5 channels can be encoded in a stereo stream..........you are referring to the source (the film maker, the DVD, etc) and not my PL II decoder in my receiver that will decode these 5 channels correct?

Yes, it happens at the source. Some game consoles, for example, will use PLII to take a multichannel track and encode it for transmission over analog stereo. The PLII decoder in the receiver will separate the channels back out. PLII encoding is new in the last several years and improves on Dolby Surround encoding. At least, that's my understanding. I'm no audio engineer and this is based on reading and posts from others who know a good deal more than I do.
post #6 of 6
Thread Starter 
Thanks Bislander.
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