Problem to achieve 4K/120Hz/8bpc/RGB resolution.

[yavordh]

Hello,

Recently I bought ASUS PG43UQ. By specifications the monitor is 43-inch 4K (3840 x 2160) VA with 144Hz refresh rate and support DSC (Display Stream Compression). Unfortunately, my current video card is Nvidia GTX 1080 (with updated DisplayPort 1.3 / 1.4 firmware), but I can’t use the full potential of the monitor, because the card does not support DSC. Currently I’m stuck at 4K/144Hz/8bpc/YCbCr422. The chroma subsampling is really annoying in Windows and I’m traying to set the monitor to 4K/120Hz/8bpc/RGB. Even the option is available and selectable in the drop-down menu of the Nvidia control panel, when I hit the Apply button the screen just goes black and after that noting is changed – settings are still 4K/120Hz/8bpc/YCbCr422. The same thing happens when I try to set the resolution to 4K/98Hz/10bpc/RGB. As I know, there is supposed to be possible to set the monitor to this setting, but in this case the 10bpc option is not showing in the drop-down menu of the Nvidia control panel (its achievable only in 80Hz).
So here are some clarification about my current settings: HDR option in Windows 10 is always set to “off”! I try several thinks, including switching with another DisplayPort 1.4 cable and another DP output from my GTX 1080, reset the monitor settings to default, reinstall Nvidia latest driver in safe mode with DDU, but nothing changes the situation. There is clearly something wrong but I have no more ideas. My previous monitor was Acer Nitro XV273K (4K/144hz), which is now half broken, but still able to show picture. When I connect it to the current system there is no problem to achieve the desired resolution - 4K/120Hz/8bpc/RGB. This make me think that there is something different with the PG43UQ, but I can figure it out what is it. The only difference between the two is that the PG43UQ has speakers. So, I wondering is it possible this feature (the sound signal, which I already disable in the Windows settings) to take portion of the DisplayPort 1.4 bandwidth and this is the reason to not be able to set the resolution to 4K/120Hz/8bpc/RGB? But these doesn’t sound to me to be the real problem here? I just want to know is there a problem with the monitor or not every monitor is supposed to supports this particular resolution settings. I ask this here, because I think this is place where people really understand of this resolution / DisplayPort 1.4 bandwidth things.

I really will appreciate some help / advice / opinion with this case.

   

[ToastyX]

If the option is there but choosing it doesn't work, then that seems like a driver bug.

[red9350]

For anyone having the same problem, i just managed to fix mine (albeit with a different monitor):

• If running multiple displays, try reducing the secondary display refresh rate. Mine was at 1080P 75Hz, had to lower it to 60Hz
• DISABLE DSC in the monitor's OSD settings, if your card does not support it! In some models it's labeled as Refresh rate overclock, or something similar
• For Nvidia cards: in the Nvidia control panel, first apply the resolution and refresh rate, and THEN use Nvidia color settings to apply 8bpc/RGB/Full
• If it's still not working, as a last resort try applying the desired refresh rate via Windows Dispaly settings instead
  

[ToastyX]

This is an old thread, but I have a better answer now. For 4K/120Hz/8bpc/RGB to work with DisplayPort 1.3/1.4 without DSC, the pixel clock must be no more than 1080 MHz (minus some overhead on some GPUs). If it's higher and DSC is not available, it will automatically drop to YCbCr 4:2:2. If the monitor is using CVT-RB or CTA standard timing, the pixel clock would be 1097.75 MHz or 1188 MHz respectively, which is too high without DSC. You would need to edit the detailed resolution for 4K/120 Hz in the DisplayID extension block and change the timing to reduce the pixel clock. "Native PC" and "CVT-RB2" are two options to try.