No HDMI audio when using Displayport MST/4k on SLI GTX 780s - AVS Forum
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post #1 of 7 Old 07-10-2014, 06:45 AM - Thread Starter
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No HDMI audio when using Displayport MST/4k on SLI GTX 780s

I'm having quite a specific problem that might need a bit of explanation of the configuration first.

I have a 4k display (Panasonic wt600) that I can drive at 60hz through displayport with full 4:4:4 colour from my GTX 780s. I recently upgraded from my logitech z5500s which were driven by multichannel analogue to a proper AV-receiver (Yamaha RXV-677). I can use HDMI to get 4k60 video but only at 4:2:0 colour which looks pretty terrible for text. Using just the HDMI output like this I can get audio to work fine with the receiver.

GTX 780s--[HDMI]--Receiver--[HDMI]--TV

However, what I want to do is use displayport to get the video signal with 4k 60hz 4:4:4 goodness and then use HDMI to send audio to the receiver

GTX 780s--[Displayport]--TV
|__[HDMI]__Receiver


. The problem is that when the displayport cable is connected to the TV and using MST, the HDMI audio output to the receiver just won't work. Windows and the Nvidia control panel detect that the receiver is connected via HDMI and the receiver detects an HDMI signal. The receiver is set as the default audio device and using the test tone from Windows just gets no audio even though the bar moves for that device showing audio should be playing. If I switch the displayport to use SST (limited to 1080p or 4k30) then the audio device starts actually working.

I'm using Nvidia 340.43 drivers at the moment and have Geforce experience installed. I have a few more ideas to test but I'm at work at the moment. I want to connect a second TV instead of the receiver to see if HDMI audio will work in that case. As far as I know the HDMI outputs on the second GPU are disabled during SLI so I want to try disabling SLI and using the second card to output audio. This isn't the solution I want for gaming though. I'm considering trying different driver versions. I'm not sure if this is a hardware limitation or a bug.

In summary, HDMI audio won't work when using MST mode from displayport. How can I fix it?
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post #2 of 7 Old 07-10-2014, 04:02 PM
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Quote:
Originally Posted by MattTS View Post
I'm having quite a specific problem that might need a bit of explanation of the configuration first.

I have a 4k display (Panasonic wt600) that I can drive at 60hz through displayport with full 4:4:4 colour from my GTX 780s. I recently upgraded from my logitech z5500s which were driven by multichannel analogue to a proper AV-receiver (Yamaha RXV-677). I can use HDMI to get 4k60 video but only at 4:2:0 colour which looks pretty terrible for text. Using just the HDMI output like this I can get audio to work fine with the receiver.

GTX 780s--[HDMI]--Receiver--[HDMI]--TV

However, what I want to do is use displayport to get the video signal with 4k 60hz 4:4:4 goodness and then use HDMI to send audio to the receiver

GTX 780s--[Displayport]--TV
|__[HDMI]__Receiver


. The problem is that when the displayport cable is connected to the TV and using MST, the HDMI audio output to the receiver just won't work. Windows and the Nvidia control panel detect that the receiver is connected via HDMI and the receiver detects an HDMI signal. The receiver is set as the default audio device and using the test tone from Windows just gets no audio even though the bar moves for that device showing audio should be playing. If I switch the displayport to use SST (limited to 1080p or 4k30) then the audio device starts actually working.

I'm using Nvidia 340.43 drivers at the moment and have Geforce experience installed. I have a few more ideas to test but I'm at work at the moment. I want to connect a second TV instead of the receiver to see if HDMI audio will work in that case. As far as I know the HDMI outputs on the second GPU are disabled during SLI so I want to try disabling SLI and using the second card to output audio. This isn't the solution I want for gaming though. I'm considering trying different driver versions. I'm not sure if this is a hardware limitation or a bug.

In summary, HDMI audio won't work when using MST mode from displayport. How can I fix it?
Funny I just hit a similar problem with a surround setup and 2 GTX 780s. I could not get audio out of HDMI connected to my receiver when the rest of my displays (connected via DP and DVI) were in a surround config. If I switched to a non-surround setup, even with all the monitors connected and enabled, everything worked fine. One other thing I noticed was that only a subset of the actual codecs available on my receiver were listed in the sound properties for the HDMI port in control panel.

After hours of trying to get it working my final solution was to use HDMI from the integrated Intel GPU for audio (I had to enable the option in my BIOS to allow the integrated GPU to function when a discrete GPU was connected), and then use UltraMon to disable the extra monitor output from the integrated GPU (a tip from Renethx I just came across perusing the "No more high end HDMI soundcards like the Asus HDAV?" thread...) Haven't spent too much time testing, but so far so good.
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post #3 of 7 Old 07-10-2014, 04:10 PM - Thread Starter
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Quote:
Originally Posted by nvmarino View Post
Funny I just hit a similar problem with a surround setup and 2 GTX 780s. I could not get audio out of HDMI connected to my receiver when the rest of my displays (connected via DP and DVI) were in a surround config. If I switched to a non-surround setup, even with all the monitors connected and enabled, everything worked fine. One other thing I noticed was that only a subset of the actual codecs available on my receiver were listed in the sound properties for the HDMI port in control panel.

After hours of trying to get it working my final solution was to use HDMI from the integrated Intel GPU for audio (I had to enable the option in my BIOS to allow the integrated GPU to function when a discrete GPU was connected), and then use UltraMon to disable the extra monitor output from the integrated GPU (a tip from Renethx I just came across perusing the "No more high end HDMI soundcards like the Asus HDAV?" thread...) Haven't spent too much time testing, but so far so good.
Thanks! It's good to know I'm not alone. I've decided to go the Intel onboard route. It was a bit of a pain to setup with the BIOS options and getting the drivers to install but it works.

I'd forgotten about Ultramon, I've already lost a couple of windows on the phantom monitor while trying to snap them to the side. I'll check the codec list to make sure everything is actually okay in that end.
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post #4 of 7 Old 07-10-2014, 06:33 PM
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First problem I hit was with WMC. When I start Live TV, audio would play for a few seconds in a loop and then I'd get a video codec error.

Solution was to disable exclusive mode in sound properties, which unfortunately means no bit-streaming. Will update if I find a better workaround, or hit any other snags.

Last edited by nvmarino; 07-10-2014 at 06:45 PM.
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post #5 of 7 Old 07-11-2014, 10:55 AM
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After further digging it looks like this problem comes if I select any speaker configuration other than stereo in the HDMI audio properties. However, if I switch to stereo, I can re-enable exclusive mode and I see Dolby Digital light up on my AVR when watching Live TV in Media Center. Seems like a bug, possibly in the Intel audio drivers? Also entirely possible it's caused by this wacky dual-display/Nvidia surround display + Intel for audio config... Should be able to confirm after a few more tests. Hopefully this is helping someone other than me...


MattTS, are you running WMC? If so, I'm very curios to know if you have any problems playing Live TV to your Panasonic via Displayport. I ask because WMC will not play protected content over a single Displayport connection, as MSFT never certified Displayport as secure for playback of protected content (even though HDCP IS supported over Displayport). However, I know that protected content will play if a Displayport display is included in an Nvidia surround configuration. As MST is effectively the same as Surround it _should_ work, but it'd be great to get confirmation...
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post #6 of 7 Old 07-12-2014, 06:25 PM - Thread Starter
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Quote:
Originally Posted by nvmarino View Post
After further digging it looks like this problem comes if I select any speaker configuration other than stereo in the HDMI audio properties. However, if I switch to stereo, I can re-enable exclusive mode and I see Dolby Digital light up on my AVR when watching Live TV in Media Center. Seems like a bug, possibly in the Intel audio drivers? Also entirely possible it's caused by this wacky dual-display/Nvidia surround display + Intel for audio config... Should be able to confirm after a few more tests. Hopefully this is helping someone other than me...


MattTS, are you running WMC? If so, I'm very curios to know if you have any problems playing Live TV to your Panasonic via Displayport. I ask because WMC will not play protected content over a single Displayport connection, as MSFT never certified Displayport as secure for playback of protected content (even though HDCP IS supported over Displayport). However, I know that protected content will play if a Displayport display is included in an Nvidia surround configuration. As MST is effectively the same as Surround it _should_ work, but it'd be great to get confirmation...
I'll try and confirm the audio codec thing myself tomorrow. Had a very busy few days so not had too much time to be able to sit down and just play with my new kit.

I use XBMC mostly rather than WMC. I don't have a TV card set up either so I can't test that, sorry.
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post #7 of 7 Old 07-13-2014, 04:22 AM - Thread Starter
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I'll try and confirm the audio codec thing myself tomorrow. Had a very busy few days so not had too much time to be able to sit down and just play with my new kit.

I use XBMC mostly rather than WMC. I don't have a TV card set up either so I can't test that, sorry.
https://www.dropbox.com/s/xs4jghwzs4...2011.20.10.png This is what I see in my supported codecs screen. Pretty sure speaker config is set to 5.1.
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