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cruzin

macrumors newbie
Original poster
Jan 24, 2008
17
1
I have a Samsung SJ55W (LS34J552WQNXZA) WQHD Monitor that supports 3440x1440 @ 75Hz. I tried using a USB-C dock that supports 4k @ 30Hz with 4k HDMI cable, but was limited to 3440x1440 @ 50Hz, which was probably a dock limitation. I then tried a HDMI 2.0 to USB-C cable plugged directly into the Thunderbolt port, but am limited to 3440x1440 @ 60Hz.

From reading, my 16' MBP should support 3440x1440 @ 75Hz, so what do I need to do to make this happen? Do I need a different cable? I have a DP to USB-C cable on the way, which supports up to 4k @ 60Hz. I would like to get a USB-C/Thunderbolt dock that supports this as well, as I have other peripherals I'd like to use. Any suggestions on a dock that can support this? Right now I will settle for anything!

If anyone has a similar setup and is getting 75hz, I'd appreciate any help. I have SCOURED the internet and forums and just can't find a conclusive answer on this. I think the DP to USB-C cable will do it, but just don't know.
 

joevt

Contributor
Jun 21, 2012
6,843
4,136
USB-C docks that include USB 3.x usually have half the bandwidth for display output. Use a Thunderbolt dock or a USB-C dock that only supports USB 2.0.

USB-C to HDMI 2.0 should be able to do 3440x1440@75Hz. You may need to add the timing using something like SwitchResX. It may be that the HDMI input won't accept the signal though.

The monitor has a DisplayPort input, so you should use a USB-C to DisplayPort cable instead. One of the reviews says only the DisplayPort input supports 75 Hz.
https://www.samsung.com/us/computin...d/34-sj55w-ultra-wqhd-monitor-ls34j550wqnxza/
 

Zubba

macrumors member
Aug 20, 2007
63
13
Try Display preferences >"option" click "Scaled" > check show low resolution modes to have the Hz control option become available to select 75hz.
 

cruzin

macrumors newbie
Original poster
Jan 24, 2008
17
1
USB-C docks that include USB 3.x usually have half the bandwidth for display output. Use a Thunderbolt dock or a USB-C dock that only supports USB 2.0.

USB-C to HDMI 2.0 should be able to do 3440x1440@75Hz. You may need to add the timing using something like SwitchResX. It may be that the HDMI input won't accept the signal though.

The monitor has a DisplayPort input, so you should use a USB-C to DisplayPort cable instead. One of the reviews says only the DisplayPort input supports 75 Hz.
https://www.samsung.com/us/computin...d/34-sj55w-ultra-wqhd-monitor-ls34j550wqnxza/
Thank you for the information on the dock! I will look into that.

I did not try a USB-C to HDMI 2.0 yet. I believe you are right that a USB-C to HDMI 2.0 will get the 75Hz, at least it should as Samsung states the HDMI 2 port should produce that. I think my dock was just hindering it.

I did actually get my USB-C to DP cable today and I am happy to report it gave me exactly what I needed! I am now able to get max resolution and refresh rate without any scaling, 3440x1440 @ 75HZ. So, if anyone else is in the same boat, I can confirm the DP cable works. If interested, this is the one I picked up:

 

cruzin

macrumors newbie
Original poster
Jan 24, 2008
17
1
Try Display preferences >"option" click "Scaled" > check show low resolution modes to have the Hz control option become available to select 75hz.
Thanks for the tip on that! I didn't know I could hold the option key and get more scaling options. I did try this before using the DP cable mentioned above, but was still stuck at 60Hz. I did however see some other resolution options, so thanks!
 
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