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 Post subject: Dolby Surround Stereo (Newb question)
PostPosted: 21 Mar 2012, 11:43 
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Like the title says this is probably a very newbish question but it's something I've not been able to work out.

I have several titles which according to lddb feature Dolby Surround, looking at the icon that looks like Dolby Pro Logic (centre, left, right, rear), is this correct?

One such title I own is Star Wars: The Empire Strikes Back (1980) [8764-85], yet when I look on the back of the packaging I see the audio listed as Dolby Surround Stereo, and under the Catalog Information it lists the film being presented in stereo.

So are these laserdiscs presented in stereo only, or something like Pro Logic which mixes down to stereo when you don't have a decoder?
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 Post subject: Re: Dolby Surround Stereo (Newb question)
PostPosted: 21 Mar 2012, 13:12 
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Dolby Surround only needs 2 mono tracks (= stereo) and encode additional information for Center and Surround.

If you listen to the soundtrack with only 2 speakers, it will gracefully play stereo only.

If you put your AV Amp in "Surround" mode, the Amp will decode the extra Dolby Surround information on the fly.

Dolby Stereo is the professional name.
Dolby Surround is the commercial name.

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 Post subject: Re: Dolby Surround Stereo (Newb question)
PostPosted: 21 Mar 2012, 13:20 
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Thanks for the explanation.
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 Post subject: Re: Dolby Surround Stereo (Newb question)
PostPosted: 25 Jun 2012, 21:05 
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yep, it's basically the same thing.
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 Post subject: Re: Dolby Surround Stereo (Newb question)
PostPosted: 25 Jun 2012, 21:57 
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hippiedalek wrote:
Like the title says this is probably a very newbish question but it's something I've not been able to work out.

I have several titles which according to lddb feature Dolby Surround, looking at the icon that looks like Dolby Pro Logic (centre, left, right, rear), is this correct?

One such title I own is Star Wars: The Empire Strikes Back (1980) [8764-85], yet when I look on the back of the packaging I see the audio listed as Dolby Surround Stereo, and under the Catalog Information it lists the film being presented in stereo.

So are these laserdiscs presented in stereo only, or something like Pro Logic which mixes down to stereo when you don't have a decoder?


Unlike Pro Logic II, Dolby Pro Logic is a decoding system only. The official name for the matrix used to encode films for Pro Logic decoding is the Dolby MP Matrix and they were identified as Dolby Stereo theatrically and Dolby Surround on home video. Often, the generic term Surround Sound or Matrix Surround Encoded was used on LD's - Chase Surround, StereoSurround and UltraStereo are also 100% compatible with Pro Logic. There are a few films that were originally released on LaserDisc with their surround tracks removed - I have no idea why. The Wiz and the first MagVid pressing of Alien had their Dolby Stereo soundtracks played through a Dolby theatrical surround decoder and then only the front channels were used for the LaserDisc. It makes no sense because Dolby Stereo has always been mono and standard stereo compatible.

Until AC-3 and DTS came along, stereo/mono compatible matrix encoding systems were the only way to experience surround sound from LD at home.
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 Post subject: Re: Dolby Surround Stereo (Newb question)
PostPosted: 10 Jul 2012, 06:47 
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you have 2 actual tracks left and right.
you have the left track info on left track. you have the right track info on right track. you have the center track identical info on both left and right tracks. -3db is applied here so the sound is even on all 3 tracks when played back. you have the identical surround mono track on left and right tracks. here 45 degree phase shift is applied(this really is time delay in miliseconds).
decoder sees that left and right has identical sound, it retracts this info and send to center speaker. it also detects delayed/out of phase sound on both tracks. it sends this info to rear speakers. left and right are already recorded discrete so these output untouched(minus retracted center and rears)
dolby digital ex works the same principal. you have the rear right and left tracks discreet. back center speakers is recorded on both rear left and right with -3db. decoder detects identical info on both tracks and retracts it. then sends it to rear center speaker or dual mono back surrounds.

thx mode on recievers apply different time phase(delay) between rear right and left as they are mono in recording.
if mastered well, matrixed recordings can as impressive as discreet surrounds.

as you can tell front left right and center is very simple math. i.e info x exist on left, info x exist on right then send it to center. info y exist on left, info y absent on right then keep it untouched. LCR seperation can be just as good as any discreen encoding( dts hd, dolby true hd included)
rear surrounds are tricky because you apply delay but same info sometimes overlaps with left and right track info then decoder gets confused. but if tech make sure surround effect info is absent on LCR but only on Surround. decoder should be able to retract it with no difficulty.
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