Sky+ HD (Amstrad DRX890) lip-sync problems when used via HDMI distribution system

Discussion in 'Sky Digital TV Forum' started by RichardG63, Mar 12, 2013.

  1. RichardG63

    RichardG63
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    Hi all. This is my first post on the forum; please go easy on me and I'd be very grateful if you would comment or advise.

    I've got a problem on a test bench. I have designed an HDMI distribution system which consists of Wyrestorm HDMI HDBaseT lite receivers & a 4x4 HDBaseT lite matrix.

    There are 2 TV's, and 3 HD sources.

    TV Locations:
    Room 1 - surround sound receiver (Marantz SR6004)
    Room 2 - LG TV (stereo audio)

    HD sources:
    Sky box 1 (Sky+ HD Amstrad DRX890)
    Sky box 2 (Sky HD multi-room box)
    Apple TV (2nd generation)

    Of the HD sources, the Sky HD multi-room and Apple TV both output surround sound multi-channel audio over their HDMI ports. The Sky+ HD box DOES NOT. With this in mind, in order to get multi-channel audio from the Sky+ HD box to Room 1 I have run coaxial audio out from the Sky+ HD box and via a digital audio (coax) matrix and then out to the surround sound receiver.

    The problem I am experiencing relates ONLY to Sky box 1 (Amstrad DRX890). Here is a description:

    When Room 2 watches Sky box 1, audio is fed to the TV over the HDMI connection. When someone watches this box in the Room 1, audio is supplied over the separate digital audio (coax) output via the digital audio matrix. Now, I notice, at times, a lip-sync issue on BOTH the Room 1 and Room 2 TVs. I have noticed that if I power-cycle Sky box 1 the issue is resolved, so I've installed a timeclock which power-cycles the Sky box 1 daily. This has not permanently resolved the problem.

    I have noticed this problem where if I switch between Sky box 1 (while noticing a definite lip-sync problem) and Sky box 2 (where the audio is always perfect), and then back to Sky box 1, I find that the lip-sync has been corrected... other times I carry out this process and notice no improvement. The gremlin appears to manifest erratically.

    I am not clear on how lip-syncing works, but a thought is that perhaps the problem is because, on Sky box 1, audio is being put out over both HDMI and the coax digital audio outputs. It occurs to me that perhaps it won't work reliably if the audio is put out over both of these outputs simultaneously. Perhaps lip-syncing on the HDMI output 'wins' over the coax output, and then it changes to prioritise the latter soon after. Or perhaps lip-syncing isn't carried out at all on the HDMI output, and it's just the Sky box that is getting confused and causing unnecessary lip-sync adjustments on the coax digital audio output...

    I wonder if anyone has experienced this problem before or might be able to shed some light on it. Thank you for reading this!
     
  2. RichardG63

    RichardG63
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    So I see that there's some speculation that Sky will be pushing out an update in the next month or so which will pass multi-channel audio out over the HDMI port... that's potentially going to resolve this issue for me.

    But still I haven't got to the bottom of this problem and would love to hear any other pro's opinions/advice...
     
  3. larkone

    larkone
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    Sky boxes do not perform any auto lip syncing but have a manual adjustment to delay sound if the video signal is running behind the sound. However Sky also manage to screw the sync between sound and video on broadcast and this is random and has been reported by many on here. Then of course there is the issue of your boxes software randomly generating sync errors that are fixed by a re-boot - typical of any computer based unit running an OS, the running software can become corrupted so it requires the big red switch fix. With my new sky box I sometimes find fast forwarding becomes jerky if the box hasn't been re-booted in a while and then becomes nice and smooth after a cold re-boot (power cycled).

    Its a computer which should tell you everything about these issues.
     
  4. RichardG63

    RichardG63
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    Thanks for the reply Larkone.

    I'm aware of the ability to delay audio within the sky box sound setup... this is indeed sometimes useful but not in this instance. Also I'm aware of (and have witnessed many times) the inconsistent quality of lip-sync with regards to the original broadcast, especially on crappy channels.

    So if the Sky box isn't adjusting the timing of the audio stream on the hdmi output and the digital audio output (coax), and presuming that the Sky box's audio delay setting hasn't been adjusted and that the broadcast has decent lip-sync, then perhaps the TV is performing some lip-sync adjustment on the HDMI input it's receiving? This seems like it would contrast with the very reasoning for combining audio and video streams on a single medium (i.e. HDMI) and perhaps this is where my understanding of lip-sync is limited in-so-far-as when HDMI is the only medium in use... but in an instance where HDMI is responsible for feeding the video and a different medium, say digital audio over coax, for the audio, then I can understand how the AV receiver is carrying out some lip-sync process to synchronise these streams.

    Confusing stuff... hope I've put my thoughts down on paper somewhat clearly. But I guess the question I'm asking is; if an AV receiver carries out lip-syncing on a HDMI video/coax digital audio signal input, can this possibly affect the output of the source?

    And where HDMI is the transport for audio & video, would a TV or AV receiver be required to carry out any lip-sync adjustment or by nature would that activity preclude the advantages introduced by HDMI as a transport designed for audio and video signals?
     
  5. larkone

    larkone
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    I think you are over complicating the issue here - nothing in the chain is performing any automatic lip-syncing. What can happen is the sound or the video can be delayed by processing or switching devices. The only one that can be adjusted is the audio where it is ahead of the video due to video processing slowing the video, then the audio can be manually delayed to compensate. As you seem to have narrowed the problem to mainly the Sky HD box then I think you are experiencing sporadic software issues in that box. I know this sounds obvious but I would first do a forced software download on the box to make sure you have the latest software and then do a planner re-build as these steps do seem to fix a lot of software based issues. My box had problems accessing on-Demand until I did a planner rebuild.

    I would also check the same on the TV as in the past people have reported syncing issues with LG TVs so make sure you have the latest firmware installed.

    If none of that fixes the issue then you will just have to blame Sky's software for being flaky - wouldn't be the first time.
     
  6. RichardG63

    RichardG63
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    It's very frustrating as I have already done a forced update, and even replaced this box with a brand new DRX895. I have experienced the same problem on the new box too... I have not experienced the same problem on the multiroom box though...

    OK so humour me then; when is lip-syncing carried out? AV receivers/processors often have a lip-sync facility built in which can be activated or deactivated. What is this facility meant to do? I always believed it was intended to synchronise audio to video when each signal is provided through a differing transport...
     
  7. wysinawyg

    wysinawyg
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    Yes, but its a fixed delay. So if you're running your audio and video through separate signal paths and the audio is always 30ms fast; you put a 30ms delay on it and all is fine.

    The description as "lip-sync" is the intention, not what is actually done, it would be better described as "audio delay" (and I think sometimes is).

    In your case the problem isn't consistent so putting in a fixed delay isn't going to help you.
     
  8. RichardG63

    RichardG63
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    Hold up... i'm not talking about the delay that can be configured on the source equipment (via Sky sound setup) but lip-sync carried out by the AV receiver...
     
  9. larkone

    larkone
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    OK understand now - the auto lip-sync in your Marantz needs a compatible TV that supports this under HDMI V1.3. The TV tells the amp how long it is taking to process the video so the amp can set the audio delay automatically. Trouble is this is not going to work if the issue is further down the line at the Sky boxes because when it arrives at the TV, the TV doesn't know if there has been any delay applied. The TV can only work out the delay it is causing not what has happened elsewhere.

    If your Tv does support this you could try turning off any CEC functions to see if that fixes it.
     
    Last edited: Mar 13, 2013
  10. RichardG63

    RichardG63
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    I'll try that. So lip-sync is really quite basic I guess... there's no resynchronisation of the input signals, only adjustment of the delay of the audio signal before it's passed to the power amps.

    Are there such devices which will look at the 'time-code' of a HDMI stream and that of a digital audio stream and synchronise both prior to passing to the input of an AV receiver? Or is this la-la land I'm imaging!?
     
  11. larkone

    larkone
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    Yes & Yes based on what the TV tells it which is averaged out from what it thinks its video processing delay is.

    2nd para - how would it know?, HDMI transmission is encrypted data packets containing the audio and video. Have a read of the TMDS section of HDMI - Wikipedia, the free encyclopedia. The errors are generated with the processing of audio /video outside of the HDMI transmission such as at the broadcast stage, your Sky box, amp or the TV
     
  12. RichardG63

    RichardG63
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    wow that info is fairly headache inducing! But if i read it right it's saying that the audio and video signal is mixed together for transmission. A processor or Sky box or whatever would have the ability to combine/split the video and audio streams.

    But there's no point in trying to synchronise audio and video that was poorly broadcast un-synchronised in the first place. But if the Sky box itself (not the original broadcast) is causing the loss of synchronicity between audio (over coax) and video then wouldn't it be nice if there were a device out there that could correct this....

    As I say, I have noticed no such problems on the multi-room Sky box, which is putting audio out over the HDMI connection. *Hopefully* the software update mentioned earlier to the DRX890/895 will negate the need to use the coaxial audio output, and therefore this will entirely rule out any 'bad processing' that the Sky box might be doing... what do you think of this thinking?
     
  13. larkone

    larkone
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    It might or it might not - pure speculation. Did you try a planner rebuild to see if that improves things?
     
  14. RichardG63

    RichardG63
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    No, not yet. By software update (in my last post) i was referencing the update that's been talked about on this forum that Sky are supposedly rolling out which will put out DD5.1 on the HDMI output...

    But I will try a force update and planner rebuild and let you know the results
     
  15. wysinawyg

    wysinawyg
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    I fear you may be disappointed with the HDMI update.

    I definitely have on/off lip synch issues with my Sky boxes when viewing via the RF connection (so where it isn't transmitting separate sound and video). I suspect the issue is more down to lack of hardware / software rigour in the Sky box combined with the integration of the hard drive etc. and everything that goes with it.

    Unfortunately the fact your multi room box works is probably more down to it being completely different, simpler hardware than the fact it sends the sound out over HDMI.
     

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