LG UltraFine 5K & Mac Pro (Late 2013): 5K resolution showing in display preferences - is it 30Hz?

Discussion in 'Mac Accessories' started by yaosiang, Feb 26, 2017.

  1. yaosiang macrumors newbie

    Joined:
    Jul 3, 2010
    #1
    Hello,

    My local Apple Store has LG UltraFine 5K monitor hooked to a Mac Pro (Late 2013) via TB3 to TB2 adapter running at 5120 x 2880 resolution.

    Based on my understanding from this forum, it is impossible to run 5K resolution via single TB2 output due to limited bandwidth of DisplayPort 1.2. Usually, 2 x TB2 outputs are required to drive a display at 5K resolution (such as the Dell UP2715K). According to https://support.apple.com/en-gb/HT207448, the Mac Pro (Late 2013) only supports maximum of 4K resolution at 60Hz.

    So could someone please explain why am I seeing 5120 x 2880 in display preferences? Is it possible that the Mac Pro is able to support 5120 x 2880 at 30Hz on the LG UltraFine 5K monitor?

    Cropped screenshot:
    [​IMG]


    Full size screenshots taken from the Mac Pro in Apple Store:

    First test:
    5120 x 2880 (File size: 28.1MB)
    https://dl.dropbox.com/s/m3eo5swfczw6uuz/Screen Shot 2017-02-25 at 18.51.22.png

    Second test:
    Default for display / 2560 x 1440 (File size: 21.1MB), please note screenshot size is 5120 x 2880 pixels
    https://dl.dropbox.com/s/6ipaeh4k9ykl462/Screen Shot 2017-02-25 at 18.50.50.png

    Third test:
    3840 x 2160 (File size: 56.2MB), please note screenshot size is 7680 x 4320 pixels
    https://dl.dropbox.com/s/e35aoer2xupc27g/Screen Shot 2017-02-25 at 18.43.54.png

    Also, how do I check the refresh rate for LG UltraFine 5K? The monitor itself does not have any buttons!
     
  2. toke lahti, Feb 27, 2017
    Last edited: Feb 27, 2017

    toke lahti macrumors 68000

    Joined:
    Apr 23, 2007
    Location:
    Helsinki, Finland
    #2
    If I'd had to guess, it might be the easiest way: 30Hz.
    Why else would they hide the refresh rate?

    I'm pretty amazed that there's so little discussion about this.
    Have die-hard mac hardware fans died?
    Or moved to other boards?

    Maybe posting this to macpro section?
     
  3. MCAsan macrumors 601

    MCAsan

    Joined:
    Jul 9, 2012
    Location:
    Atlanta
    #3
    As I remember there are documented hacks for getting 5K monitor to work on Mac Pro. You have to connect one TB cable to each of the two system busses.
     
  4. toke lahti macrumors 68000

    Joined:
    Apr 23, 2007
    Location:
    Helsinki, Finland
    #4
    UltraFine has only ONE tb-port...
     
  5. MCAsan macrumors 601

    MCAsan

    Joined:
    Jul 9, 2012
    Location:
    Atlanta
    #5
    My bad. I was thinking of how folks has connected Mac Pro to 5K monitors using dual TB2 connections doing MST.
     
  6. yaosiang thread starter macrumors newbie

    Joined:
    Jul 3, 2010
    #6
    Short version:
    Although Mac OS X is reporting the monitor to be running at 5120 x 2880, according to SwitchResX the actual output to the display (tested on 2015 rMBP) is 4096 x 2304 at 60Hz.

    Long version:
    I went back to Apple Store to test the LG UltraFine 5K monitor with a Mid 2015 MacBook Pro 15" with Radeon R9 M370X dGPU. The results are exactly the same as the tests I did on Mac Pro (Late 2013), except the colour output was 8-bit on the rMBP as opposed to 10-bit on the Mac Pro. The resolution was 5120 x 2880 under Display Preferences and System Report. The image size of screenshots are also 5K resolution.

    Cropped screenshot from rMBP:
    [​IMG]

    However, interestingly SwitchResX is showing that the resolution output to the monitor is 4096 x 2304 at 60Hz scaled to 5120 x 2880. I guess that confirmed the theory that a single TB2 link can only support 4K max and we cannot rely on System Report to show the actual output resolution from the GPU.

    [​IMG]
    I did not have the chance to test if I could create a custom resolution in SwitchResX to drive the display at 5120 x 2880 30Hz. Anyone would like to guess if that will work?
     

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