Sky+ and surround sound question

Discussion in 'Sky Digital TV Forum' started by gebbel, Jan 31, 2009.

  1. gebbel

    gebbel
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    I recently connected my Sky+ receiver to the Sony HT-SF1100 amp via optical. I notice that with some channels, however, the 2 rear speakers do not output coherent sounds..rather muffled broken incoherent sounds. This happened , for example, when I recorded the recent Liverpool v Everton FA cup game from Setanta. However when I play Bubble hits...I am getting 5.1 sound from all speakers.
    Is it a case that, with some channels, you just can't get 5.1?
    By the way I have the "Optical Output" in the Sound Menu set to "Dolby D" instead of "Normal".
    Thank you.
     
  2. Steve N

    Steve N
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    Absolutely. press the i (info) button to find out what the sound is for that particular programme.
     
  3. pcbbc

    pcbbc
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    That's not 5.1 - Only a few channels have 5.1, such as Movie and HD channels. Also your amp should show you if you are receiving Dolby Digital or not.

    What you are getting is Dolby Surround/ProLogic. This can be carried as part of any normal two channel analogue stereo (or digital encodings thereof) by phase encoding the 2 "extra" channels into the 2 channel signal. It has a centre channel and a single reduced bandwidth rear channel going to both rear speakers. A lot of programmes are recorded in ProLogic, including music and most CDs (hence why you get surround on the music channels). However there is no indication on Sky to tell you if a recording contains Surround or not.

    It's all very cleverly done so that the added channels are not noticeable on a standard stereo receiver, but can be extracted from the signals by a ProLogic capable receiver. A case of 4 into 2 will go sometimes ;)

    I strongly suspect Setanta is not Surround encoded and doesn't broadcast 5.1 (I don't have it, so please correct me if I am wrong). So the noises you are hearing form the rear channels are your amps attempts to decode the non-existent matrix encoding of the rear channel. Switch your amp to standard stereo mode if you want to avoid these unwanted artefacts.
     
  4. gebbel

    gebbel
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    Just after watching a pretty poor :thumbsdow Arsenal performance on Setanta, but at least I had sound from the rear speakers! On the Amp, it says "PL II". What does that indicate?

    Thanks again
     
  5. pcbbc

    pcbbc
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    Dolby ProLogic II.

    ProLogic (I) has a single rear channel as I described above. It could be implemented in simple analogue electronics 1976 style if you wanted to, although today's implementations are all done digitally.

    ProLogic II takes exactly the same DolbySurround encoded input (i.e. 4 channel L+R+C + reduced frequency mono rear) and creates separate phantom full range left and right rear channels by using digital signal processing logic. It should be emphasised though that these separate channels are not "real" - they are derived digitally by processing the exact same information in the stereo signal that is available to any ProLogic decoder.

    Still the amp saying PL II doesn't mean the recording actually contains PL II (you will never see a show labelled "in DolbySurround II where available") - there is no DolbySurround II encoding, only DolbySurround. It just means that the ProLogic II decoding is enabled at the decoder, so it will try it's best to extract the stereo encoding from the source 2 channel input, if it exists.

    Having said that, PL II decoding is meant to be an improvement over original PL but obviously not as good as a real 5.1 signal because that has dedicated separate channels.
     

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