RX6900XT HDMI 2.1 issues.

[minaelromany]

I have 3 major problems with a newly purchased RX6900XT GPU that never occurred on GTX 1070Ti I was using.

This is connected to a LG OLED C9 TV.

First issue:

The GPU is limited to 4k/120hz 10bit 4:4:4 RGB or 4k/60hz 12bit 4:4:4 RGB in windows but not 4k/120hz 12bit 4:4:4 RGB.

RTX 3080 is outputting 4k/120hz 12bit 4:4:4 RGB just fine as I tested it once.

This seems to be a 40Gbps cap on AMD's HDMI 2.1 implementation that was never mentioned and I have no idea whether this is a hardware limitation or it can be fixed with a driver update to give us full 48Gbps HDMI 2.1 bandwidth as it supposed to be,

Second issue:

4K HDR videos do not run in 12bit or 10bit YCbCr 4:2:2 format and the only option is 10bit YCbCr 4:2:0 and that is not good.

Again, both GTX 1070Ti and RTX 3080 support 12bit YCbCr 4:2:2 just fine.

Third issue and worst of all:

No HD audio via HDMI for RX6900XT with any refresh rate less than 100hz.

I am trying to watch movies from my PC connected to LG OLED via HDMI 2.1 and using madVR to auto detect movie framerate which is usually 24p results in No HD audio at all. No TrueHD, no DTS-HD MA, no Atmos and no DTS:X.

It also happens if I set the system's refresh rate to anything lower than 100hz using ANY media player.

Only when I set refresh rate to 100 or 120hz, I get HD audio fine.

I connect the GPU to the TV then TV to AVR using eARC.

I always use bitstreaming and had no issues with the same exact setup with GTX 1070Ti GPU I upgraded from. I am using MPC-HC with Lav Filters and madVR but the same issue happens with PowerDVD and DVDFab Player and Movies&TV Windows 10 app so it is definitely the RX6900XT.

Even games output no audio when refresh rate is less than 100hz.

I connected the GPU to AVR then to the TV and audio works fine with all refresh rates but of course I lose 4K/120.

 

[Riptide]

The panel is not a 12 bit panel yes? I'm not sure what the reward there is for running 12 bit then?

When I drove my 65C9 with my 6900xt I kept it in 4:4:4 RGB FULL, 120hz 10bit. Didn't experience many issues there although I did get some occasional glitching on the screen that was intermittent and not persistent. That is not a problem with the CX I have now, same cable.

You might want to post on avsforum and see if you can get some assistance there.

 

[minaelromany]

The panel is not a 12 bit panel yes? I'm not sure what the reward there is for running 12 bit then?

When I drove my 65C9 with my 6900xt I kept it in 4:4:4 RGB FULL, 120hz 10bit. Didn't experience many issues there although I did get some occasional glitching on the screen that was intermittent and not persistent. That is not a problem with the CX I have now, same cable.

You might want to post on avsforum and see if you can get some assistance there.

It is not a 12bit panel indeed but running 12bit has its benefits of more headroom according to Vincent Teoh from HDTVtest.

Unfortunately I was banned from AVSforum many years ago due to something stupid (forgot I even had an account there since 2001 and made a new account when they changed the layout so they perma banned me for having multiple accounts).

Can you run refresh rate of windows at 24hz and get audio via eARC?