Cable-Is Dolby encoded like Sky?

Discussion in 'Sky Digital TV Forum' started by Shady Deal, Feb 11, 2002.

  1. Shady Deal

    Shady Deal
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    Hi All,
    Have recently had Telewest cable put in and use it on a TV in the bedroom. (Pace Box 4100 I think).

    Reading back through the archives it doesn't seem clear if Dolby Pro logic is encoded in the stereo signal you receive like it is with sky.

    Can someone confirm this, as for various reasons I have unsubscribed from Sky and am thinking of getting the boxes swapped around, i.e. Sky upstairs cable downstairs as the picture seems ok on cable at the moment.

    I have no wish to test this however if everything I watch on cable will be only in stereo.

    I have a Tosh 46 RPTV.

    Thanks
     
  2. LV426

    LV426
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    It is nigh-on impossible to remove "prologic" encoding from a prologic encoded stereo signal, except by making it into mono ie by mixing the two channels.

    Therefore, if the original source was a prologic encoded stereo soundtrack, and it is transmitted in stereo, it WILL retain its prologic elements. So long as you are wired for stereo from your box to your amp, the prologic elemts will be preserved.
     
  3. Shady Deal

    Shady Deal
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    Cheers Nigel,
    So in a nutshell it will be no different than I am watching through Sky at the moment??

    Regards
     
  4. Guest

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    Hi,

    I think nigel is wrong! When I had my digital tv fitted by telewest, they said that NONE of the programs would be in dolby prologic, because they were using 'true stereo sound', his words not mine! What ever that means!
     
  5. Shady Deal

    Shady Deal
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    Cheers for the reply, now I am really confused??

    So anything I watch will only come out of the front left/right speakers?? or the Stereo effect will mean you get only two channels?? 1 Channel left front and back and 2nd Channel right front and back??

    Think I might have to leave the setup as it is, just a shame to have to use the Sky Box purely to get surround sound.

    Regards
     
  6. Guest

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    newsposts,

    I assume you will only get 2 channels, but check with telewest! What I know is they said that this 'true stereo sound' is better than pro-logic! I'm not that bothered about cable tv with surround sound (most of the channels are ****e!!), as long as I have it for my DVDs!! Cheers
     
  7. Shady Deal

    Shady Deal
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    Cheers Mr UFO, guess you're right, I'm the same as far as the DVDs go!! I don't know if anyone in telewest would have the knowledge to explain properly. The installer didn't know.

    Would this work as a test:-

    a) Record using scart from telwest box to my nicam VCR a programme/film that is on BBC1 etc.

    b) Replay tape in VCR connected to my RP and see if the sound effect is the same?

    Thanks Again
     
  8. Guest

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    Er, it could work?! I'm not that technically minded when it comes to this kind of thing!
     
  9. LV426

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    1) ProLogic is a clever way of mixing the various sound elements that make up a soundtrack into two channels. A ProLogic decoder takes the left and right channel signals and uses intentional differences in phase between left and right to steer the various sound elements to the left, right, centre and rear channels.

    2) Like paint, once sound is mixed, it cannot be unmixed.

    3) I can't be 100% sure, but, to the best of my knowledge:

    If the source material has been mixed to contain these phase differences, it cannot be unmixed. Therefore a prologic decoder will find these differences and generate a Dolby Surround output. I don't believe that there is anything Telewest or anybody else can do to unmix - ie remove - ProLogic elements from a stereo soundtrack - except by mixing the two channels into mono.
     
  10. Shady Deal

    Shady Deal
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    Cheers Nigel,
    I would agree in what your saying but i guess until i connect it up I will not know for sure!

    Thanks again.
     
  11. bob007

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    Stereo is stereo whether you call it Nicam or True.....as long as you have the audio fed to an amp or connected to a tv via scart you will be able to listen to stereo/dpl depending on your equipment.
    Lets face it, they don't know one end of a scart lead from the other..........:clown:
     
  12. MarkB

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    Nigel is correct. No matter the transport medium, the Dolby Surround encoded signal will remain intact.

    Mark
     
  13. Darth Vader

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    In addition to the other replies.

    Dolby Pro Logic is the consumer (home cinema) version of Dolby Surround or "stereo variable area" (SVA for short) which has been used in cinemas since the 1970's.This called a 4:2:4 matrix

    When a feature film or TV program is mixed, a plain stereo(non SVA) copy is produced on to a 6 track tape or disk, a Dialogue 2Trk, Music 2Trk & Effect 2Trk (DME for short) is created, this then can mixed down to a new stereo master if required giving a plain non DPL soundtrack. This in theory could be used by your cable company for their broadcasts, I dought this though as it would be quite expensive to do. My guess is that your cable supplier is running normal DPL soundtracks like everyone else.

    One thing to keep in mind is that DPL processors still do a quite good job of decoding a non DPL stereo mix, like TV soap operas and music.

    This is because the DPL processor looks for left and right signals in the soundtrack and routes them to left and right, exactly the same as the original. Any in phase mono information in the soundtrack the DPL processor routes to the centre channel (most dialogue is mono so it to gets routed to the centre channel) then any out of phase infomation (very slightly delayed) is routed to the surround channel.

    The great thing about DPL is that it is compatable with mono playback,stereo playback & Pro Logic playback.

    Thats the best laymans terms I can come up with. Check Dolby's web site for more info (www.dolby.co.uk).

    Sorry to get technical, I hope you now understand Pro Logic a little better.
     
  14. Shady Deal

    Shady Deal
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    Mr Vader,
    Cheers for that!! The force is sure with you!!

    Telewest engineer has confirmed that DPL "IS" in their digital stream.

    Regards
     

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