New LG Ultra Wide Monitor - No Audio via displayport?

Discussion in 'Mac Pro' started by steveOooo, Feb 3, 2016.

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  1. steveOooo macrumors 6502a

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    #1
    Just got a LG Ultra Wide Monitor 34" display - slowly getting used to it - pretty much like two 20" monitors without the bezel.

    The monitor has built in speakers and would be nice to use when not using my 2.1 external speakers.

    I have it connected via Displayport and I was under the impression DP carries audio as well as video?

    The monitor has DP 1.2 enable / disable - its currently disabled as I was getting some flicker when enabled. Does this matter?

    Also im using an old cable from circa 2008 - would using the supplied cable do anything?

    Ideally I can set the monitor's volume to high then adjust using the apple keyboard
     
  2. ActionableMango macrumors 604

    ActionableMango

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    Sep 21, 2010
    #2
    I get audio over DP, but only in Windows, not in OS X. In my case this is a known issue with Nvidia and there's an enabler KEXT out there somewhere. In your case it should be working fine because you're using the stock AMD.

    I also had to disable DP 1.2, so that's not it either.

    You might as well try the cable it came with. That's troubleshooting 101.
     
  3. steveOooo thread starter macrumors 6502a

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    #3
    I actually now have the AMD R9 380 pc card - the hdmi doesnt work on this card so maybe DP doesnt either. Ive updated my sig as have only had it 6 days or so.

    Ive also tried the much shorter white lg cable and its the same so at least we know DP cables are pretty much the same

    Ive enabled DP 1.2 and all seems fine - no glitches - not sure if theres any point in running 1.2 vs 1.1. when nothing new happens
     
  4. DearthnVader, Feb 3, 2016
    Last edited: Feb 3, 2016

    DearthnVader macrumors regular

    DearthnVader

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    #4
    The problem is Apple EFI Rom graphics cards build custom properties in the device tree that are needed for HDMI/DisplayPort Audio. Your PC Bios doesn't build these properties in the device tree, so you get no audio.

    You can try http://forums.macrumors.com/threads/guide-hdmi-audio.1499797/

    I don't know if it works with DisplayPort, and I don't know if the Audio chip on your AMD card is supported by OS X, but give it a shot.

    Edit: I took a quick look and the AMD R9 380's Audio Chip is supported by OS X, so you should be able to get this working with HDMIAudio.kext.

    You have to disable SIP in 10.11.x. and add kext-dev-mode=1 to your boot-args.

    Here's the kext http://www.blanca.com/HDMI/
     
  5. h9826790 macrumors 604

    h9826790

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    #5
    Agree withdearthnvader, you need to install the HDMIAudio kext. However, there is no guarantee that the driver will work.

    Apart from disable SIP and kext Dec mode = 1. My understanding is that 5,1 firmware may also be required (most of the 4,1 can be flashed to 5,1), and EFI of the GPU may also affect the result. In my own experience. I have exactly the same card (R9 280), same machine, same OS. If I boot with Mac EFI, audio via DP works. If boot with non EFI VBIOS, audio no work. It may be coincident, may be related.
     
  6. steveOooo thread starter macrumors 6502a

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    #6
    It shows DP in the audio settings but its greyed out - how do i 'add kext-dev-mode=1' ?
     
  7. cerberusss macrumors 6502a

    cerberusss

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    #7
    On the command line, enter something like this:
    sudo nvram boot-args="kext-dev-mode=1"
     
  8. steveOooo thread starter macrumors 6502a

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    #8
    Didnt work I added 'sudo nvram boot-args="kext-dev-mode=1"' in terminal within my signed in account (normal usage)
     
  9. h9826790 macrumors 604

    h9826790

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    #9
    Which OS? SIP disabled?
     
  10. steveOooo thread starter macrumors 6502a

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    #10
    SIP Disabled and running 10.11
     
  11. h9826790 macrumors 604

    h9826790

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    #11
    I don't think there is any EFI for R9 380 yet, so, can't test it. But for my R9 280, when I boot it without EFI, the HDMIAudio driver won't work.
     
  12. steveOooo thread starter macrumors 6502a

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    #12
    Ok sounds like it's a no go and have re enabled SIP

    Speakers on the monitor are pretty woeful though so not a huge loss. I can always plug some USB speakers into the back of the monitor for better than Mac Pro internal speakers
     
  13. DearthnVader macrumors regular

    DearthnVader

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    #13
    Unfortunately, HDMIAudio.kext was never open sourced, so there's no way to update or debug it. Either it works or it doesn't.
     

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