L1KVM - 4PC to 1 monitor not going over 100HzxRGBx8bxHDR at 3840x1600

Hardware Other Hardware
1

Hi,

I just recently got the 1.4 Display Port KVM Switch 1 monitor to 4 PCs.

My setup is a gaming rig (with 3090RTX), work laptop and Mac Mini - they are connected to KVM which then is connected to Alienware AE2821DW (3840x1600). For laptop and mac mini I do not care that much about refresh rate and colors above 8 bpc, however for gaming ring I am a little bit dumbfounded. I have both sides (rig and monitor) connected with Club3D CAC-2067 cables.

It seems that I cannot go over 100HZ at a native resolution to get any other color format than horrible YCbCr422 which causes color banding. Even switching this around at 100Hz requires choosing the option in panel couple of times.

I can easily get 120hz 10bit YCbCr444 with HDR when connected directly, the 144hz is also possible with 8bpc at RGB with HDR. When I use KVM this option is not even available in Nvidia Panel.
When I set the option up directly and then switch cable - it causes the screen to show one frame every couple of seconds or so.

I also used my previous cables from KabelDirekt that could also push this through direclty and through some no-name DP switch I used previously that could also push this, so I am really surprised that the KVM cannot move it. The 1.4 bandwidth should be able to push this easily.

Any ideas what I can do to get this to work or what to try out @wendell ?

EDIT (instead of commenting own post)
The standard IT magic happened - when I contacted support the problem resolved itself - I tried unplugging everything yet again and plugging to third port just the rig and boom - suddenly 3840x16000 @120Hz @ 10bpc (YCbCr444) + HDR working. I have no clue why this works now and did not previously.

I plugged all the other stuff and it seems to work now

Any idea what I can do to test this to see what caused it?

3

Probably external interference. We try very hard not to do anything with digitally retiming the signal because

also push this through direclty

“Directly” doesn’t matter. Its counterintuitive. Think of it as you are standing in the port of the gpu looking down the signal pathway. If we want to maintain gsync/freesync timing as precisely as possible, the kvm is invisible. Instead of a relay race where its signal > thing repeating the signal > signal its just signal >> signal. The kvm tries to be invisible. insodoing your gpu sees BOTH cables as one long contiguous corridor. Its counterintuitive. If you have one thing causing interference or it doesn’t get a good handshake you’ll have issues.

You can create a custom profile and set the res that way; sometimes even ddu will resolve those kinds of issues. Software has more to do with than most people realize. The kvm itself otherwise is a big dumb switch, by design, so everything else has the best shot of working.

glad its working fine now.