4k@60Hz

Discussion in 'MacBook' started by mscq, Apr 11, 2015.

  1. mscq macrumors newbie

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    Apr 11, 2015
    #1
    Probably a subject beaten to death but:

    Ars Technica has reviewed this machine and using a third-party dongle managed to get the new Macbook to drive a 4k display at 30Hz through MST mode.

    Apple's own support page states that you can get 4k @30Hz through HDMI using their own USB-C Digital AV adapter, but you can also get 60Hz via SST.

    What can the machine actually do? I'm fine with just one port and slightly lower performance but I would like to hook it up to a 4k display when I'm at home so I can use it as a desktop. Any information? The available info out there seems really inconsistent and it'd be great to get some real world confirmation.
     
  2. iscajal, Apr 11, 2015
    Last edited: Apr 11, 2015

    iscajal macrumors member

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    Apr 10, 2015
    #2
    If the specs as given are right, the picture is pretty clear-cut.

    The rMB supports USB 3.1 Gen 1 at 5Gbit/s in hardware, which is too slow for UHD@60Hz. So no matter what actual protocol you run on, there's simply not enough bandwidth in hardware to push the amount of pixels required for that.
     
  3. mscq thread starter macrumors newbie

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    Apr 11, 2015
    #3
    Weird. Maybe it's a typo on Apple's part if they are claiming 60Hz capability over SST? Or perhaps it is still possible over Displayport?

    Either way, Ars seems to say it's already choppy at 30Hz so 60 might not even solve smoothness issues.
     
  4. iscajal macrumors member

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    Apr 10, 2015
    #4
    Odd. But I guess we'll know once someone tests it. :)

    UHD@60hz requires upwards 12Gbit/s of bandwidth. Maybe that's separate from their USB-C stack, or maybe the linked document is wrong. *shrugs*
     
  5. ctyrider macrumors 6502a

    ctyrider

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    Jul 15, 2012
    #5
    USB3 / 5Gb/s bandwidth has nothing to do with rMB inability to support 4K/60Hz. USB-C supports DisplayPort 1.2 in AltMode. DP 1.2 signal is multiplexed over 4x USB-C lanes, and not carried as USB data. Therefore USB3 data bandwidth is irrelevant here.

    What's relevant is HD5300 GPU not having enough horsepower to drive 4K at 60Hz. It can do 4K at 30Hz, but even that is a crappy experience according to Anandtrch testing.
     
  6. iscajal macrumors member

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    Apr 10, 2015
    #6
    Thank you for elaborating, I didn't know about DP piggybacking over that. :)
     
  7. mscq thread starter macrumors newbie

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    Apr 11, 2015
    #7
    I just got off Apple's online store chat. Basically, they said that 60Hz is achievable using a USB-C to DisplayPort adapter but that they don't make one so you have to resort to 3rd parties. I know Google and Monoprice have USB-C to DP adapters.

    Maybe someone will make a charging/DP/usb-A multi dongle soon.

    As for ctyRider, I've read that Intel states their chip is capable of driving 4k/60 but using active cooling. It'd be really interesting to have someone with the actual devices to test this out.
     
  8. iscajal macrumors member

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    Apr 10, 2015
    #8
    I'll be happy if it can push the pixels for a 2560x1600 without crashing and burning. :)
     
  9. ctyrider macrumors 6502a

    ctyrider

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    Jul 15, 2012
    #9
    It's correct that 4K at 60Hz is achievable over USB-C with DP cable. But not on 12" MacBook. See ArsTechnica review of rMB - they connected it to Dell 4K display using Google USB-C to DP cable. It only comes up at 30Hz, and they weren't impressed with the performance.

    Basically, I wouldn't bother trying to run 4K display on this generation of rMB.
     
  10. mscq thread starter macrumors newbie

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    Apr 11, 2015
    #10
    Good catch. I had misread and didn't notice Ars had used a Displayport adapter. I guess Apple is wrong in stating it could do 60. Here's hoping the next gen will be able to handle it with ease. I wonder if it'll take a year before they refresh it. Looks like I might have to hold onto my 2011 Air for a little bit longer.
     
  11. iscajal macrumors member

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    Apr 10, 2015
    #11
    If I read that correctly, looks like the GPU supports SST, but not MST - most 4K panels are still MST (two tiled panels merged into one in hardware/software).
     
  12. chleuasme macrumors 6502

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    Apr 17, 2012
    #12
  13. ctyrider, Apr 11, 2015
    Last edited: Apr 11, 2015

    ctyrider macrumors 6502a

    ctyrider

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    Jul 15, 2012
    #13
    It's interesting though.. Apple's own Using 4K Displays support page states the following:

    Dell P2415Q display used in ArsTechnica test is most certainly an SST display.. But the review says "we had to put our Dell P2415Q into MST mode to make it happen"..

    I am starting to wonder if Ars 30Hz sync and poor performance is due to lack of P2415Q support in special build of 10.10.2 that the reviewer unit likely had. And if may see better results with 10.10.3, with display running 60Hz/SST. The plot thickens..
     
  14. mscq thread starter macrumors newbie

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    Apr 11, 2015
    #14
    That's what I was interested in. Apple's own support doc and someone on their site chat had confirmed that 4k60 was possible but Ars seemed to say not so.

    I would really like to see someone test it on a P2415Q with DisplayPort under 10.10.3
     
  15. SlickVik macrumors member

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    Sep 12, 2003
    #15
    That same Apple support doc also states Mac Mini 2014 supports 4K @ 60hz using SST which is not the case - I updated to 10.10.3 and hooked up the P2415Q using DisplayPort and the maximum resolution it supports is 2560 x 1440.
     

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