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I bought an ultra wide monitor (LG 29UM58) the other day. To hook it up to my Air, I convert a mini-DP signal to HDMI. With two different cables, I started noticing occasional latency on the signal where the screen freezes for about a second and then it becomes responsive again.

Some more interesting tidbits:

  • This happens on my laptop screen as well as the external monitor while I'm connected to the display.
  • I can use the on-screen menu of my monitor while my screen is frozen.
  • I never had this issue with my previous screen, a 16:9 Full HD monitor with a DVI port.
  • I tried an AmazonBasics Mini-DP to HDMI cable (maximum resolution of 1920x1080) as well as a Mini-DP to HDMI adapter from an obscure brand together with an HDMI-to-HDMI cable. Both gave the same results.
  • I'm using macOS Sierra on a 2015 MacBook Air.
  • My new monitor's native resolution is 2560x1080.
  • The issue only seems to manifest while I'm moving my mouse, so there seems to be some interplay with mouse input and display output. I haven't seen it happen while I type yet.
  • I tried reproducing the issue while a video was playing. Most of the time both the pointer and the video froze, but sometimes only the pointer froze. This makes me believe it's not related to the monitor itself or the cable.

How can I find out what's causing the random freezes and fix the issue?

  • What brand/model is the new monitor? From years of experience with many different 3rd-party MDP > HDMI adaptors, very few actually work well, if at all. I recommend BELKIN branded MDP > HDMI adaptors. [Disclaimer: satisfied customer of BELKIN products - no financial stake in the company.] – IconDaemon Mar 7 '17 at 18:41
  • It's an LG 29UM58. – Pieter Mar 7 '17 at 20:40
  • I don't think it's related to the adaptor, because I noticed that sometimes my pointer freezes but a video elsewhere on the screen keeps playing. – Pieter Mar 11 '17 at 13:20
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More than likely, the issue is, in fact, your Mini DP to HDMI adapter.

The AmazonBasics Mini DisplayPort to HDMI Adapter adapter that you listed is a passive adapter (notice nowhere do they say "active"). Additionally, is much less expensive than an active converter like the Cable Matters Active Mini DisplayPort to HDMI Adapter

Passive vs. Active

So, what's the big difference? A lot, actually. A passive adapter, to make a long story short, basically takes the pin outs of the Mini Display Port and configures them as HDMI. Most of the time, this works, however there are a lot of limitations. For example, the signaling of HDMI is 5V while mDP/DP is 3V. Some monitors don't like this. Additionally, HDMI has a clock signal where DP doesn't.

An active adapter addresses these issues; there's actually a chip that does the conversion of the DP signal to a "proper" HDMI signal with the correct voltage and clock signaling.

A Microsoft engineer has an excellent blog post on this very subject

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Just to address some of the points in your question to reduce confusion...

  • Your OSD has absolutely nothing to do with the display coming out of your Mac. It's an "overlay" that comes from the monitor and if you computer hangs, it will continue to work. It will even work if no video source is connected to your monitor at all.

  • If it happens on both screens, your computer is hanging because it is probably getting bad signals coming back from the monitor.

  • You never had issues before because you were going native DP to DP.

  • There's really no "interplay" between your mouse (or keyboard) and your GPU - one doesn't affect the other. A video may crash for a number of reasons, none of which will be your mouse. What you are seeing is your CPU/GPU having to "deal" with the video conversion of two very different signals.

  • Interesting theory. Both cables I tried are indeed passive. But with my previous monitor I used a simple mini-DP to DVI cable, which worked fine. And does the passive adapter theory have an explanation for why it doesn't seem to happen as long as I don't move my mouse? – Pieter Mar 11 '17 at 19:27
  • It's not a theory; there's a reason for active adapters and it's because converting interfaces is flaky to begin with. As stated in the answer, it previously worked because it's native DP to DP. As far as your mouse goes, I believe you are associating "coincidence" with causation. The mouse is attached to the USB bus and your video is attached to DP which is ultimately attached to the PCIe bus – Allan Mar 11 '17 at 23:59
  • Looks like I'm gonna have to look out for another new adapter then. Thanks for sharing your insight! – Pieter Mar 12 '17 at 18:00
  • Currently considering buying amazon.co.uk/dp/B00S0BWR2K, which seems to comply with all the requirements. – Pieter Mar 12 '17 at 19:19
  • using this active adapter now, it's been good so far: amazon.com/Vantec-Vlink-Usb-C-Converter-CB-CU300HD20/dp/… – arturomp Mar 10 '18 at 2:07
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I had similar issue when connecting my MacBook Pro to projector using HDMI. The issue happened from both direct HDMI and from MiniDP to HDMI. The MacBook froze with blank screen and nothing on the projector either. I just tested with MiniDP to VGA and Connected VGA to the projector. This ran without any freezing problem. Unfortunately I had to revert to yesterday's technology.

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