Sound advice needed - Dolby Pro Logic

Discussion in 'LCD & LED LCD TVs Forum' started by Mike246, Mar 18, 2005.

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  1. Mike246

    Mike246
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    I have Sky+ connected to a Toshiba 32WL48 and Toshiba Home Cinema system. The Sky system connecs to the TV via a high-quality scart.

    There are two basic options for feeding Sky sound to the Home Cinema. Either an optical feed from the Sky decoder or a dual phono feed from the TV. The benefit of the second is that when I switch the TV on and off the sound switches with it.

    The question is - does the phono feed from the TV contain the Pro Logic signals so that if a film is broadcast with multi-channel audio it will be decoded?
     
  2. boab_is

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    if you use the optical output from the sky+, you will get Dolby Digital from any broadcasts that carry it.

    i think sky movie channels + 24 on sky one are currently carrying it.

    I watched bad boys 2 in DD from sky movies, and it sounded pretty darn good. :smashin:

    the vast majority of programs are still only in stereo or pro-logic however
     
  3. patrik_f

    patrik_f
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    The optical signal is digital, and would normally get you the better sound since most likely your surround sound processor is better at producing analogue sound than your Sky-box.

    In addition it is a good thing to break some of the ground loops in your system with an optical connector.
     
  4. Alan111S

    Alan111S
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    To answer your q, yes the pro=logic data is encoded within the stereo mix. I would go for both options, so you can have Pro-Logic even for programmes watched through the aerial.
     
  5. Mike246

    Mike246
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    Guys,

    Thanks. I need to phrase the question slightly different. I am an ex-BBC design engineer so I should know all the answers. Trouble is in my day, we only had mono sound and had to wait for the valves to warm up.

    If I use the optical output from Sky+, clearly I get all the sound channels multiplexed through. I prefer to use the phono out from the TV as the sound will switch off when I turn off the tele.

    Question is - if I do this, do I still get the rear speaker information through to the Home Cinema or is it lost?
     
  6. jon2099

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    Short answer- yes. Pro Logic (and PLII) is simply multi-channel sound encoded into a stereo soundtrack. The AV receiver performs the separation from stereo into multi-channels.
     
  7. jimsan

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    Your Toshiba Cinema system will have Dolby Pro-Logic, Pro-LogicII or Pro-LogicIIx. Basically this system takes a standard Nicam Stereo signal and rearranges it into its own version of 5.1 sound. Pro-Logic divvies this up into Front Left, Front Right, Centre and Rear. (4 channels really + A Sub output). PLII gives you Rear Left and Rear Right too. The 'x' version adds pseudo centre rear too.

    However, this is not 'proper' 5.1 DTS or Dolby sound. To get this from your system you need the optical connector between your Sky+ and the Toshiba (or from a DVD). As mentioned before Sky broadcast a limited number of Movies with this 5.1 signal.

    If I was you I'd use the system with the Phono outs from your TV most of the time, but keep an eye out for the odd Sky broadcast with the 5.1 signal then specially select the optical input on your Tosh on these special occasions.

    Jimmy
     
  8. ianh64

    ianh64
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    Mike

    To clearup any confusion between Jon2099 and Jimsans posts, DPL surround information is encoded in the stereo soundtracks. If you listen to the soundtrack with equipment that cannot decode the DPL information, you will get the stereo version. If you have a DPL decoder, it will decode the encoded information and use the surround speakers as intended by the sound engineers. Many films will be transmitted with their existing DPL soundtrack so this will be true DPL.

    However, if you use a DPL encoder on a pure stereo source, some of the information in the stereo source may be decoded as surround infomation and this will be reproduced as ambience in the surrounds. As there is nothing in the source that is specifically encoded for one speaker or another, this can be best thought of as a pseudo surround. As Jimsan says, it 'rearranges it into its own version of 5.1 sound'.

    It is often overlooked that processing multichannel sound requires many different tasks. At the very least there is the decoding (into multi channel audio) and the steering of the sound to different speakers. Many of the DSP options can work on a different number of channels. DPLIIx for instance, will quite happily take a 5.1 mix and convert it in to 7.1. In this case, the decoding may be from DD, DTS (that you get via a digital connector from your STB/DVD player box) encoded material or from stereo source using the built in decoder. However, in all these cases, DPLIIx surround processing can be applied to the decoded sound whether it is 2 ch analogue audio or multi channel digital sound.

    -Ian
     

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