Image lag with external monitor connected

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Level 1

72 points

Image lag with external monitor connected

Hi all.

My old external monitor just called it a day, so I bought a new one. A 4k Samsung U28D590. Pretty lousy video quality compared to my old one, but I can live with that, I got it for next to nothing.

The big problem is the poor "speed feeling"; mouse cursor movement is definitely laggy compared to the internal screen (I use video mirroring, so I can compare the screens in real time). Not much, but definitely enough to drive me pretty crazy. This calls for veeery delicate mouse movements, almost as with an old PC if you know what I mean, otherwise I "miss" buttons and other GUI things I want to click because I overcompensate my movements, so to speak.

The monitor is connected via HDMI. I've read stuff about HDMI not providing the highest possible refresh. Can I expect better results if I connect via Thunderbolt/DisplayPort? If so, I would need an adapter between mini-DP and DP. Would this adapter have to meet any special specifications?

My question is not similar to other people's questions since my internal screen behaves correctly. Any ideas?

(If you do have an idea, please do not mark your response as "correct answer" before checking with me, thank you.)

MacBook Pro with Retina display, OS X El Capitan (10.11)

Posted on Apr 9, 2016 8:09 AM

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Answer 1

750 H2C Author

Level 1

72 points

Apr 10, 2016 1:31 AM in response to Grant Bennet-Alder

Yes, that sounds extremely counter-intuitive considering the fact that the cursor on the internal screen shows no lag (video mirroring, both screens run simultaneously). If the CPU manages to push the cursor around on the internal screen, then it can't be the reason for the laggy cursor on the external monitor. It must be something in the connection or settings of the external monitor, right? Or maybe it's just a very slow monitor?

Regarding problem solved: Nope, last time I posted, the first guy who answered marked his solution as correct without checking with me – and it wasn't. Killed the entire thread.

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Answer 2

Apr 9, 2016 8:56 AM in response to 750 H2C

mouse cursor movement is definitely laggy

It is counter-intuitive, but the most frequent cause for laggy mouse-tracking is 'using up all the CPU cycles', NOT slow refresh on the display.

Try running Activity Monitor's CPU display showing all processes, or download and run an etrecheck report.

PS> the original Poster is the only one who can mark replies as 'solved my problem'. But it the system encourages you to do so by asking you trick questions along the way.

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Answer 3

750 H2C Author

Level 1

72 points

Apr 10, 2016 1:48 AM in response to Grant Bennet-Alder

When I watch CPU usage while I'm moving my mouse for a minute, nothing in "User" consumes more than a few percent, and the same goes for the "System". Around 96% inactivity should mean that the CPU is probably not the bottleneck.

I googled the Samsung U28D590 for the same problem and found that there are a few users out there experiencing exactly the same thing. So, this monitor goes back to where it came from.

First I will test with another cable, though. Far-fetched, but if hifi freaks can experience any difference by changing speaker cables, maybe it will solve my problem? 🙂

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Answer 4

750 H2C Author

Level 1

72 points

Apr 10, 2016 1:56 AM in response to 750 H2C

Tried another HDMI cable but no luck, just as bad.

Then I tried a DisplayPort-to-HDMI adapter, and now the input lag is far shorter than with pure HDMI. Still not as good as with my old 1920x1200 monitor, but maybe I can live with it. I'll evaluate and see. I have 30 days to return the monitor if I'm not happy with it.

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Answer 5

750 H2C Author

Level 1

72 points

Apr 11, 2016 5:56 AM in response to 750 H2C

Problem solved. I bought a MiniDP-to-DP cable: no lag whatsoever. So: stay away from HDMI.

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