4k monitor on HDMI has much less frame-rate compared to 1080p on HDMI for tirple 4k dock

This is for the UD-ULTC4K triple 4k docking station.

I know that the HDMI port is supposed to be 30Hz (as opposed to the display ports which are 60hz). But the 4k monitor on HDMI seems way slower than 30hz because the frame rate looks fine when I connect a 1080p monitor to HDMI. Like the framerate for 4k on HDMI is slow that I’m barely able to use it.

Or is this just expected behaviour that 4k monitors on the HDMI port on the dock have a significantly slower frame rate compared to 1080p on the same port?

My setup:

  • MacOs 12.3.1 (21E258) (Monterey)
  • Macbook 16", M1 Pro
  • displaylink 1.6.1
  • monitors: acer 4k nitro 28.5"

Hello,

Thank you for contacting Plugable support! Sorry to hear about this issue. I’d be more than happy to assist you.

“I know that the HDMI port is supposed to be 30Hz (as opposed to the display ports which are 60hz).”
The HDMI port is only limited to 30Hz at 4K. Under 4K, it can offer higher refresh rates (up to 60Hz).

So for example, 4K @ 30Hz on the HDMI port will feel much slower than if say a 1080p @ 60Hz monitor were to be used from the same HDMI port.

So if you are seeing a performance decrease when using 4K vs 1080p from the same HDMI port, this is normal and expected behavior.

“Or is this just expected behaviour that 4k monitors on the HDMI port on the dock have a significantly slower frame rate compared to 1080p on the same port?”
That’s correct. The HDMI port is unable to operate at greater than 30Hz at 4K but will operate at 60Hz for 1080p.

Please don’t hesitate to let us know of other questions.

Thanks again for contacting Plugable support and best wishes!

Joshua Henry
Senior Engineer | Product Owner
Plugable Technologies

@Joshua_H Ok makes sense. What about a 1440p monitor on the HDMI port, will I then be able to get 60hz?

Edit: according to this https://plugable.com/products/ud-ultc4k it seems like only 1080p and 1200p is available in 60z for the HDMI port. Is that right?

A 1440p display would work at 60Hz!

For reference we also have the supported resolutions listed on our specs page:
https://plugable.com/products/ud-ultc4k#nav-specifications

Hope this is helpful!

Best wishes,
Josh