Will the use of a Hub (like Hub+) provide better image

Discussion in 'MacBook' started by Sander25, Jun 17, 2015.

  1. Sander25 macrumors newbie

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    Jun 4, 2015
    #1
    Can anyone confirm that using a Displayport or Mini Displayport connection to an external monitor provides a better image quality than with HDMI? Using HDMI, the rMB assumes it is a TV and the image quality on external monitor is horrible. Pixelated and washed out text etc. Get a headache using it. Tried to force RGB mode but no success.

    Can anyone confirm that use of MDP or DP provides real 2560x1440 resolution (like a Thunderbolt display) ?

    Thanks...!
     
  2. cfedu macrumors 65816

    cfedu

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    #2
    DP should be able to deliver 2560 x 1440 on a display that has that resolution and a DP input
     
  3. fatefulwhisper macrumors regular

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    #3
    Depends on what type of monitor you have. I've seen on this forum that some users have specific DELL monitors that can output 2560x1440 under HDMI. I have a 27" DELL monitor (UH2713M) that I already bought, and it also does only 1080p via HDMI, and 1440p via DVI or DP. Since there isn't any "hub" that allows you to do mini-DP to DP as of right now, what I ended up doing was using Apple's USB-C AV adapter, I bought a $3 HDMI to DVI cable from ebay and that worked perfectly... I have full 2560x1440 via DVI for now.
     
  4. cfedu macrumors 65816

    cfedu

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    #4
    A HDMI to DVI adapter can't to 2560x1440. DVI only supports 1200P, a dual link DVI can support 1600P/1440P but I have never heard of a HDMI to DL DVI cable/adapter.

    http://store.apple.com/ca/product/MJVU2AM/A/apple-hdmi-to-dvi-adapter?fnode=51&fs=f=duallinkdvi-hdmi&fh=36d5%2B3034%2B3058

    I know that the above adapter would not work at 1440P


      • Supports single-link DVI devices up to 1920x1200 resolution.
     
  5. Mr. Buzzcut macrumors 65816

    Mr. Buzzcut

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    #5
    He is using the Apple AV adapter. Since the signals are the same (just a different plug) the capability should be dictated by the AV adapter. What you posted about DVI is accurate at 60Hz. Here is what Apple says:

    "This adapter allows you to mirror your MacBook display to your HDMI-enabled TV or display in up to 1080p at 60Hz or UHD (3840x2160) at 30Hz. It also outputs video content like films and captured video. Simply connect the adapter to the USB-C port on your MacBook and then to your TV or projector via an HDMI cable (sold separately)."

    http://store.apple.com/ca/product/MJ1K2AM/A/usb-c-digital-av-multiport-adapter?fnode=51
     
  6. cfedu macrumors 65816

    cfedu

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    #6

    He's using a 3$ HDMI to DVI adapter


    Not saying that it's impossible, but from my understanding you can not do more than 1200P with DVI.

    If he is using an active HDMI to DL DVI adapter, then it would work. I do not think such an adapter exists and if it does, it would be more than 3$ The active mDP to DL DVI adapter from Apple is 120$.
     
  7. fatefulwhisper, Jun 17, 2015
    Last edited: Jun 17, 2015

    fatefulwhisper macrumors regular

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    #7
    Just to be clear, yes, I'm getting full 1440p @ 60Hz.

    I'm using Apple's $80 AV Multiport adapter AND the HDMI to DVI cable (which is just a passthrough) like this one: http://www.ebay.com/itm/HDMI-Male-t...t=LH_DefaultDomain_0&var=&hash=item1e9e25970b

    It's Apple's AV Multiport adapter that is doing the heavy lifting in terms of resolution. The cable is simply just a pass-through (or adapter), if that makes any sense.

    The monitor I have is the DELL U2713HM, which is capable of 1440p on both DVI (dual link) and DisplayPort. HDMI is only 1080p.
     
  8. fatefulwhisper, Jun 17, 2015
    Last edited: Jun 17, 2015

    fatefulwhisper macrumors regular

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    #8
    I can understand that it's probably hard to believe that an $80 adapter + $3 HDMI->DVI cable works, but I am uploading photos as proof that it works. Feel free to ask me any questions about how this setup works, but it should be pretty self-explanatory (I hope). I've got absolutely no reason to lie that I can get 1440p; what could I possibly gain by lying about that?
     

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  9. zhenya macrumors 603

    zhenya

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    #9
    What happens if you connect to the hdmi port directly instead of converting to dvi? The earlier comments are correct - single-link dvi has a maximum resolution of 1200p, so it's not that we think you are lying, it's that we see that you are having issues, and that conversion is likely at the heart of it. I've seen cables like the one you have cause all sorts of issues, so that's definitely where I would start.

    Never mind - I see your comment in the last post that hdmi is limited to 1080p...
     
  10. fatefulwhisper macrumors regular

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    #10
    I'm using dual-link dvi... I'm not having any issues w/ conversion.
     
  11. fatefulwhisper, Jun 17, 2015
    Last edited: Jun 17, 2015

    fatefulwhisper macrumors regular

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    #11
    Not sure why people are assuming I'm using single-link dvi. I'm uploading an image that shows a diagram of what DVI cable ends look like. For reference, I bought a cable that uses the 4th one down (Dual-link). You can see it pretty clearly from the ebay picture link too... Also, if you don't like ebay, you can buy it from amazon too: http://www.amazon.com/Gefen-HDMI-Ca...qid=1434603489&sr=8-4&keywords=hdmi+dvi+cable

    There's others that cost a bit more, but work the same:
    http://www.amazon.com/s/ref=nb_sb_n...k+cable&rh=i:aps,k:hdmi+dvi-d+dual+link+cable
     

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  12. zhenya macrumors 603

    zhenya

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    #12
    I know you are using what appears to be a dual-link cable. My point is that from experience, I've not generally seen these kind of conversion cables operate quite as specified. If you have a poor quality picture, some kind of conversion is happening - it HAS to be. Most likely your signal is being converted to 1200p at the monitor side, then scaled poorly by the monitor. See post #16 here. http://forum.notebookreview.com/threads/hdmi-to-dvi-d-2560x1600-adapter.717288/page-2
     
  13. zhenya macrumors 603

    zhenya

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    #13
    Further, if you look at the hdmi Wikipedia page and the section on dvi compatibility it mentions repeatedly that it is single-link compatible. I suspect those extra pins for dual link are not actually wired to anything. If you look at the pin outs, that would make sense, as hdmi carries the picture signal on 6 pins, as does single-link dvi. Dual link dvi splits that to 12 pins, which would require your adapter cable to split the 6pin hdmi signal into 12 pins. Not happening on a passive cable.
     
  14. cfedu, Jun 17, 2015
    Last edited: Jun 17, 2015

    cfedu macrumors 65816

    cfedu

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    #14

    Never called you a liar, just found it hard to believe. DVI is pin for pin the same as HDMI and that is why only passive adapter is required. HDMI to DL DVI required some active adapting.

    From my understanding it could not be possible. I have tried in the past to do the same thing with my Macbook air and a dell 3007. I used a mDP to HDMI to DVI and mDP to DVI. The only solution was to buy the the 120$ apple adapter.

    If you google HDMI to dL DVI adapter, all you will find are unsuccessful attempt to get older monitors to above 1200P. I think this is a great find as I don't think many would think it would work. There must be some active conversion happening in the Mac or the Apple Adapter.

    Thanks for explaining
     
  15. fatefulwhisper macrumors regular

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    #15
    I'm not arguing that you're wrong by the way; I guess I'm not 100% certain that the passive cable is dual or single, so I won't refute you on that on. I will say that I'm definitely not getting audio, of course. However, I'm definitely seeing full, native 1440p resolution. I know what upscaling looks like, if that's what you're referring to, and this is definitely not upscaled.

    I'm not a hardware expert by any means, all I can say is that it works for me. If you read the specs for Apple's USB-C AV Adapter carefully, the HDMI max output is 4k @ 30Hz. I'm able to achieve 1440p which is much less than that, and at 60Hz. My guess is that all the "conversion" is happening on Apple's AV adapter, and the cable is simply passing it through. From the HDMI wikipedia page: 'No signal conversion is required when an adapter or asymmetric cable is used, so there is no loss of video quality'
     
  16. fatefulwhisper, Jun 18, 2015
    Last edited: Jun 18, 2015

    fatefulwhisper macrumors regular

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    #16
    Ok. Never used that monitor before, but I encourage you to try my solution w/ the Apple AV adapter + HDMI->DVI cable and tell me that it does not work (unless of course, your DVI input can't go higher than 1200p, then ignore). You can always return the adapter to the apple store within 14 days and get a full refund. As for the cable, it's only $3, but you can probably find one for less than $1 on ebay. If you can't wait for shipping, try to find it at your local computer store where you can return it for a full refund in case it doesn't work.

    The max resolution for Apple's HDMI->DVI adapter is 1200p as specified on their website, so that makes sense you weren't able to go higher. I have no idea how their adapter works, but the cables don't seem to work the same way; they are bi-directional too. Apple's AV Multiport adapter's max resolution is 4k via HDMI.
     
  17. fatefulwhisper macrumors regular

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    #17
    I'd also like to add that some users on this forum have been able to use the Dell U2715HM (which is a newer version of the monitor I'm using) with success to get 1440p via HDMI, so that's a much better solution if you're in the market to getting a new monitor; no conversion cables or adapters necessary; just Apple's own AV adapter, and an HDMI->HDMI cable.
     
  18. zhenya macrumors 603

    zhenya

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    #18
    No disagreement there - HDMI 1.4 is capable of bandwidth adequate for 4k@30hz, but that's not really relevant to what you are doing here. Read my post about the pinouts again - hdmi to single-link DVI works because it is a straight 6-pin to 6-pin passthrough, although it will be limited to 1920x1200p resolution by the DVI connection in the display you are connecting to as per the DVI standard. Dual-link DVI gains its extra bandwidth by doubling the number of pins carrying the RGB signal, from 6 to 12. With 6 pins, single-link DVI is limited to 3.96Gbps of bandwidth (after overhead). Dual-link DVI is capable of 7.92Gbps by doubling the total number of pins to 12 (3.96x2). While HDMI 1.4 is capable of 10.2Gbps over 6 pins. In order for your adapter to function as you think it is, the DVI portion of the cable would either have to split the 6-pin HDMI signal into 12 pins somehow (while still being low on bandwidth compared to the maximum potentially carried by the HDMI output source) or force more than the 3.96Gbps onto those 6 single-link pins. It's not possible without some sort of active conversion, which is why it isn't working for you.

    Again, the Wikipedia article goes out of its way several times to mention HDMI compatibility with single-link DVI only.

    https://en.wikipedia.org/wiki/HDMI
     
  19. fatefulwhisper, Jun 18, 2015
    Last edited: Jun 18, 2015

    fatefulwhisper macrumors regular

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    #19
    Ok, not arguing the technical specifications. Again, I'm not very hardware savvy so I can't explain how/why it works. If you can tell me some sort of test or command I can try on my macbook to tell me that I'm actually running at 1200p, I'm all ears... I'd be skeptical too, if I was looking at all the specifications as well.

    The only way I can prove it is by running this command on terminal:

    Code:
    $ system_profiler SPDisplaysDataType |grep Resolution
    Resolution: 2560 x 1440 @ 60 Hz
    
    If you know of any other test I can do, please let me know. If you're skeptical, then so am I. But honestly speaking, this whole argument is kind of moot once USB-C hubs/adapters (that can power the macbook and have mDP) become more ubiquitous. Because Apple didn't come out w/ one first, I'm forced to use this solution for the time being, but it's only temporary. I still have a mDP to DP cable sitting on my desk from my previous (MBA) laptop. Once they make a USB-C to mDP adapter, I'm no longer going to be using DVI anyway.
     

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  20. zhenya macrumors 603

    zhenya

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    #20
    Sorry - in your specific case all I can do is speculate that there is something happening to the signal after it is output from the MacBook. It's clear both from the specifications, Internet reports from other people, and your own issues, that output of HDMI to dual-link DVI is not possible.

    Re-reading some of your earlier posts, what you need is a usb-c to displayport adapter like this https://store.google.com/product/usb_type_c_to_displayport_cable. That will work fine. The problem, of course, is that you can't charge with that cable, but in short order, hubs will be available that should integrate usb ports and displayport output. At the moment you are stuck in an edge case where you have a monitor that doesn't support its own resolution over the provided HDMI connection, and don't have a way to feed it the necessary dual-link DVI signal.
     
  21. fatefulwhisper macrumors regular

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    #21
    Yup, that pretty much sums it up. And yes, I've already purchased and tried that cable (about 7 weeks ago), and it works perfectly; I get audio + video (@1440p); however, I cannot power the laptop at the same time.
     

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