KVM guidance: Connect LG 27GP950-B to 1080 ti and two macbooks

Hello all, I’m having trouble figuring out what KVM switch to choose for my use case, and I would really appreciate some guidance.

Here are the peripherals I would like to connect:

  • LG 27GP950-B. Monitor with one DP 1.4 input and two HDMI 2.1 (FRL6) inputs. It supports 4K@144hz over DP 1.4 with DSC and uncompressed over HDMI 2.1. Supports GSync and Freesync. LG also claims to support “overclocking” up to 4K@160hz, but only over DP with DSC and VRR enabled (aside: I don’t understand why this is “overclocking”; it should be within spec for HBR3 with DSC and any timing). I don’t care about HDR, this monitor has terrible local dimming anyway.
  • Ducky Shine 7. USB keyboard with n-key rollover and 1000hz polling. Has some customer RGB drivers, but the functionality can also be controlled by keybinds and physical switches. Other than that, I don’t think there is anything unusual about it.
  • Razer Deathadder v2. USB mouse with 1000hz polling.
  • Razer Kiyo. 720p USB webcam.
  • Blue Snowball. USB mic.
  • Scarlet Solo 3. USB audio interface.

And here are the machines:

  • Windows PC with GTX 1080 ti. The GPU has three DP 1.4 outputs and one HDMI 2.0b output. It does not support DSC. The motherboard (Intel z390) has multiple USB 3.1 gen2 outputs (ie, 10G).
  • M1 Pro Macbook Pro. Has one HDMI 2.1 output and three TB4 ports. It supports DP 1.4 alt mode with DSC.
  • M3 Macbook Air. Has two TB4 ports supporting DP 1.4 alt mode with DSC.

Important note: Although some Intel machines are apparently able to send HDMI 2.1 over TB4 (no idea how this works to begin with), M1/M2/M3 machines are limited to HDMI 2.0b over TB4, and my understanding is this comes out of the 10G lane allocated for USB 3.1 gen2.

And here the requirements, ordered and grouped by priority (I realize all probably cannot be satisfied, but I need all the P0s and most of the P1s to justify spending this much money):

  • P0: Connect the PC and at least one of the Macbooks to the switch (ie, I’d settle for physically swapping inputs between the Macbooks if needed to meet the other requirements).
  • P0: Run at least 4K@120hz on all connected machines.
  • P0: Minimal “jank” (no display flickering, failure to wake machine after switching inputs, etc).
  • P1: Preserve VRR capability of all connected machines.
  • P1: Macbook(s) are connected to the KVM through TB4 dock(s) (ie, require only one TB4 connection each).
  • P1: Connect all three machines to the switch.
  • P1: EDID emulation for the PC.
  • P2: Run max supported refresh rate on the Macbooks (4K@144hz).
  • P2: Upgrade path to 4K@160hz or at least 4K@144hz for the PC if I ever get a new GPU.

I was originally looking at the ConnectPro DP 1.4 KVM switches, which satisfy nearly all the requirements on paper. Unfortunately, my monitor is part of a specific product family that is not compatible with their switches. I reached out to their support, and they told me it lacks the ability to detect the level of DP support for each connected machine, and therefore would be limited to DP 1.2. That doesn’t entirely make sense to me (how can it negotiate a connection with even one machine in that case?), but I’m going to take their word for it.

I’m now looking at either the 4x1 or 2x1 Level1Techs 1.4 Display Port KVM Switch, possibly with an EDID repeater in front of the PC. I’m not sure of the exact bandwidth requirements of all the other peripherals, but I’m thinking 5G should be sufficient. Few final questions:

  • Max supported resolution and refresh rate for the Level1Techs KVMs is not clear from the product page: “up to 4k/120hz or 8k/30hz” and “overclocking not supported”, but also “DisplayStream Compression Supported”. My understanding is that 4K@144hz and even 4K@160hz are still within spec for DP HBR3 with DSC. What is a realistic expectation here?
  • Is the Level1Techs EDID repeater likely to work here, or would it be subject to the same issue as ConnectPro called out? Does it interfere with VRR or DSC?
  • Any other obvious issues I haven’t considered?

Edid emulation and vrr on displayport is problematic and likely go be buggy. Full stop. There is no fix for this. Fundamental problems. Modern os doesnt really require edid emulation which is misunderstood in the first place.

Dp alt mode kvms are not recommended if you want high res and refresh.

Our dp kvms work with lg and vŕr.

Hdmi 2.1 kvm doesnt disable vrr and makes the pc think the monitor is still there but this does not mean vrr is going to function in a bug free way
And you may still need to disable it . But the hdmi 2.1 kvm doesnt force disable it.

Thanks Wendell, I’m going to try one of your DP 1.4 KVMs.

Be sure to grab the optional nvidia dp1.4 firmware update

I’ve been using the KVM for a few days now. Overall, it works very well. My main concern was the lack of EDID emulation, but this turns out not to be a big deal for my use case. I don’t have any problems with application window resizing on either OS. Maybe this would matter more with additional displays not managed by the KVM (eg, if the laptops were not in clamshell mode).

The USB device switching is very nice too. I have my keyboard plugged into one of the USB ports and everything else attached through a hub. The keyboard is immediately detected, regardless of sleep state. The devices attached through the hub take a few seconds, but nothing fails to detect.

No issues with image quality/stability either (I’m running 4K@120hz with DSC off for now, due to a limitation with the monitor). I’m sure it helps that I got a fresh set of 1m DP 1.4 cables from club3d. I’m using a short USB-C → DP 1.4 cable from cablematters for the macbook dock. not recommended, but doesn’t seem to cause any problems.

Great device, I will definitely be keeping this one.

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