[Solved] Artifacting with KVM + high refresh

Hey folks. I’ve had the L1T single monitor dual PC KVM for about two years. I was able to use it to share my 3440x1440 120Hz G-Sync monitor (AW3418DW) between my windows pc and mac work laptop, without issue.

Today I picked up an AW3423DWF, a 3440x1440 165Hz Freesync HDR monitor. I’m able to get a 165Hz signal through with HDR enabled, but I see flashing horizontal line artifacts. Brief video (I can’t include links): youtube com watch?v=YweXQ–l7ew

  • If I connect my PC directly to the display, I do not see this artifacting.
  • If I lower the refresh rate down to 100Hz, I stop seeing artifacting (appears at 120Hz and 144Hz).
  • If I disable HDR on the display, I can run at 120Hz without artifacting, essentially the same mode as my previous monitor.

I don’t know if that means it’s bandwidth related or not, I don’t consider it a “fault” of my KVM unit unless told otherwise. I know any of the high refresh performance with these are not explicitly guaranteed, and it’s largely “people have seen success, YMMV”. I searched a bit and didn’t find a direct answer to this.

Has there been success running a combination of high refresh (>120Hz) and HDR?

And importantly, I’m considering buying a dual monitor KVM to run both of these displays off of the same PC. I’m wondering how likely it is that I can do 165Hz+120Hz.

Thanks in advance.

Hi! Thank you for posting, and welcome to the forum!

When I try to go to your link it’s giving me a “This video isn’t available anymore” error.

https://www.youtube.com/watch?v=YweXQ–l7ew
^ this is the link, right? Also, you should be able to post links now.

All of your setup should be fine, especially being that it is 1440p.

The KVM can do up to 240Hz HDR with DSC (display stream compression) and 120Hz HDR without DSC.

Can you tell me what cables you’re using?


Also btw we do have a guide if you would like to browse it:

Thanks Amber! Looks like I mangled the URL when it was modifying it into text: L1T KVM Artifacting - YouTube

I had skimmed the FAQ but maybe it was because I was hoping I wouldn’t have to go and buy a bunch of cables to test replacements, heh.

I don’t know what useful information I can answer with, but both the PC → KVM and KVM → display are full displayport on both sides, no conversions. I got them from the IT office at work, can’t speak to “quality”. The first leg is probably 6 feet and the other is probably 4 feet.

I wouldn’t be surprised if you tell me that it could be signal degradation now that I’m trying to pump more information (HDR). Maybe 120Hz no HDR was the limit.

If you can’t identify anything else or provide more troubleshooting suggestions I can see if I have short DP cables and test my existing setup?

EDIT: Nope, don’t have any shorter DP cables. Hoping not to have to buy shorter cables just to test this, since I need a pretty decent length from PC to raised standing desk.

I should have properly read the FAQ, the “Importance of length” section surprised me. I’d have expected the KVM to almost act like a signal booster. Maybe that means 10ft is too much for these cables at HDR 120Hz+?

I was hoping Monoprice was on the list of tested cables given their cost. I may just have to try short Club3D cables and see if I can get HDR 165Hz from my KVM and rule out any issue with the KVM?

given alienware is sometimes picky, you’d probably be best off with fibbr brand fiber optic cables.

Can’t put a repeater in the kvm and have freesync/gsync work properly in all scenarios.

Just dropping a quick update in here for posterity. I’m currently running two 2-meter (6.5ft) Club3D cables with the KVM in between and experiencing no artifacting (that I’ve noticed) at 165Hz with HDR. Fingers crossed I won’t have to fork out for the Fibbr cables.

I also picked up a Club3D 3m (9.8ft) cable for the 120Hz monitor, since I’ll be mounting it up a ways. I’m pretty confident it’ll work.

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