42LG7000 fails to output Dolby Digital through optical

Discussion in 'LG TVs Forum' started by techguydtvuk, Feb 11, 2009.

  1. techguydtvuk

    techguydtvuk
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    Despite turning the "dolby digital output" option in the Audio menu to ON... the set (42LG7000) only outputs a 2channel stereo signal. Most infuriating as the manual and the specs - and the on-screen menu confirm a dolby digital output mode on the optical audio port.

    connecting the hifi to the skyHD box optical port direct cures the problem, but what about the faulty tv output? Very annoying as I have multiple HD sources (PC, BlueRay, and SkyHD) so I have to keep disconnecting optical cables, when all I should need is one optical cable going from the tele to the hifi.

    Who else has noticed?
     
    Last edited: Feb 11, 2009
  2. ptruman

    ptruman
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    I believe it will only output DD from the DVB-T source, and in the UK, there is no 5.1 transmission. Upshot : no 5.1 output.

    You've already done what I have, and routed sound via other means - although I still use the TV optical out to get sound from my SCART etc sockets...
     
  3. techguydtvuk

    techguydtvuk
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    not so according to LG's website and instruction manual.. which is why i've logged it as a fault with them. Apparently, the optical port should simply 'passthrough' whatever is being input into the tele.. be that DD5.1 via HDMI input or off-air from DTT where available.. But instead, what is currently happening, is that somewhere in the tele, the dd5.1 signal input via HDMI ...from say .. a blueray player or Sky HD.. is being understood, and then converted or downsampled to 2 channel stereo on the tv's optical port. That shouldn't be happenning - the port should be passing through whatever it gets from the source. Does anyone follow what i'm saying?

    Hopefully they can come up with a firmware fix.
     
    Last edited: Feb 12, 2009
  4. sebbelcher

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    This has been brought up before. I think the problem is that when HDMI devices do their 'handshake' the player device asks the TV what it's capabilities are and TV replies "I'm a 1080p capable display with 2.0 stereo speakers" so the player will only send stereo sound information.

    I think if it were possible to trick the player into sending 5.1 data, then that is what would get passed through, as I can't see the TV decoding the 5.1 then re-encoding it into 2.0 digital.

    Alternatively LG could update the firmware to enforce this when you have Dolby Digital Output enabled.
     
  5. techguydtvuk

    techguydtvuk
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    Downsampling is a standard feature of many encoder/decoders and DACS.. but having said that your theory seems very plausible. In fact, your suggestion that the firmware should be tweaked to enforce 5.1 output when handshaking with HDMI devices, whilst the dolby digital output is enabled in the tv menu.... is by far the best workaround I've heard.

    As you pointed out.. the fact the tele isn't working like this right now, is indicative of a handshake problem with the set sending back the wrong information when it's own dolby output option is set to enabled!

    Is anyone at LG listening / know about/ care about this?
     
    Last edited: Feb 12, 2009
  6. sebbelcher

    sebbelcher
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    Probably not, but it is something I would really like to be fixed. I have a laptop with a Blu-Ray player and HDMI out, which works wonderfully except I can only get 2.0 sound on my 5.1 system.
    Being a laptop it doesn't have much in the way of audio connectivity and the only digital audio out is through the HDMI so the only way I could achieve 5.1 at the moment is to but an expensive HDMI capable hi-fi receiver, which I don't want to do!
     
  7. dwhite

    dwhite
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    Where in the manual does it say it passes thru Dolby digital?

    Only thing I can find is from p97:

    which agrees with what ptruman states (and how I also understand it to work) that its only from broadcasts it receives via its internal tuner, not externally connected devices.

    Lots of TV's have optical outputs on them, to future proof them for when (if) freeview ever broadcast dolby digital, but I have never yet found a tv that will switch Dolby Digital thru it from externally connected devices.
     
  8. techguydtvuk

    techguydtvuk
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    Have you reported the problem to LG tech support?
     
  9. techguydtvuk

    techguydtvuk
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    Toshiba's (and the set I replaced the LG with) can do it. It's all in the "handshake" protocol which is updatable in the firmware - if LG choose to. The TV should simply tell the HDMI device "I am a 1080p capable display with 5.1 dolby optical out enabled" instead of "Iam a 1080p device with 2.0 speakers" - which it is currently doing - regardless of the optical output selection in the tv menu.

    Doesn't really require much change... for a fuller enjoyment.
     
  10. dwhite

    dwhite
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    Which toshiba was it, as I say this is an unusual feature most just pass stereo. Of course unless the set has a dolby digital decoder built in, you would lose access to audio from the TV's own speakers, when its passing Dolby Digital thru it from external devices.

    I've had experince with Toshibas in the past where they wouldn't pass any external devices audio (not even stereo) thru the optical only the freeview tuner output.
     
  11. Jonsen

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    Any updates on this? Thanks :)
     
  12. madsod

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    its the same on my older 42 " lg so i dont think you will get a fix
     
  13. dwhite

    dwhite
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    AFAIK its the same for every TV not just LG, other than a Toshiba the OP mentions, but as he doesn't state the model number we can't confirm this functionality.
     
  14. Chewi

    Chewi
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    Any new information on this? I've just discovered this problem myself and it's really frustrating. It's thrown a spanner in what has already been a very problematic setup.
     

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