Getting a MBP to Display 60 Hz 4K

[dvm258]

I am having trouble getting my 2018 MacBook Pro to output 4k at 60 hz to my new external display. I am only able to get a 30 hz picture.

According to the technical specs for my computer, it should support 60 hz at 4K:

https://support.apple.com/kb/SP775?viewlocale=en_US&locale=en_US

Simultaneously supports full native resolution on the built-in display at millions of colors and:

• One display with 5120-by-2880 resolution at 60Hz at over a billion colors
• Up to two displays with 4096-by-2304 resolution at 60Hz at millions of colors
• Up to two displays with 3840-by-2160 resolution at 60Hz at over a billion colors

However, according to this Apple Support page for the multiport adapter I am using (model A2119), only 2020 13-inch models can output at 60 hz with it. https://support.apple.com/en-us/HT207806

• 3840 x 2160 at 60Hz with these devices:
  • 16-inch MacBook Pro introduced in 2019
  • 15-inch MacBook Pro introduced in 2017 or later
  • 13-inch MacBook Pro with four Thunderbolt 3 ports introduced in 2020
  • MacBook Air introduced in 2020
  • Retina iMac introduced in 2017 or later
  • iMac Pro
  • iPad Pro

What gives? Is this some kind of limitation of the adapter? If so, why is it a limitation that only applies to certain MacBook Pro models? If I got another adapter, or connected directly to USB-c via Displayport, will I still be able to get a 60 hz picture?

The whole situation with the adapter supposedly supporting 60hz, and my computer also supporting it, but NOT that specific combination, is perplexing to me. Though admittedly it's very Apple.

 

[avkills]

I would try getting a Thunderbolt > DP cable that is rated for that res.

 

[davegoody]

On my previous Mac, which had MDP ports, in order to display 60Hz 4K I needed an ACTIVE MDP to HDMI adapter. For my current 2019 iMac which has USB-C / TB3 ports, I purchased a cable that supported 60Hz 4K and it just worked. Not all cables are the same.

 

[Amethyst1]

What gives? Is this some kind of limitation of the adapter

You need a Mac with DisplayPort 1.4 in order to get 4K at 60 Hz from this particular adapter. Your MBP's Intel graphics only support DisplayPort 1.2, limiting you to 4K at 30 Hz using this adapter.

 

[joevt]

You need a Mac with DisplayPort 1.4 in order to get 4K at 60 Hz from this particular adapter. Your MBP's Intel graphics only support DisplayPort 1.2, limiting you to 4K at 30 Hz using this adapter.

Yes, this. The MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports) just has an Intel GPU which only supports DisplayPort 1.2 (it has no DisplayPort 1.4, DSC, or 4:2:0).

The Apple USB-C Digital AV Multiport Adapter is like a USB-C Hub. USB-C has four high speed lines. The hub uses two of them for USB 3.0 (one for transmit and another for receive), leaving only two lines for DisplayPort lanes.

Two lanes of DisplayPort 1.2 can only do 4K 30Hz (8bpc RGB HDMI, 10bpc RGB not HDMI, 10bpc 4:2:2 HDMI). DisplayPort 1.2 doesn't support DSC or 4:2:0 so it cannot do 4K 60Hz using those methods. You need four lanes of DisplayPort 1.2 to do 4K 60Hz 10bpc RGB. Therefore you need a Thunderbolt dock, or a USB-C hub that does USB at only USB 2.0 speed, or an adapter that doesn't include USB 3.x.

DisplayPort 1.4 has 50% more bandwidth than DisplayPort 1.2, so it can do 4K 60Hz 8bpc RGB with just two lanes but it can't do 8bpc RGB HDMI 2.0 timing, or 10bpc RGB (required for HDR). To do 4K 60Hz 10bpc with two lanes of DisplayPort 1.4 requires DSC or 4:2:2 or 4:2:0. Apple's adapter supports DisplayPort 1.4 and DSC on the input (DSC works in Catalina but may be gone in Big Sur?)

 

[posguy99]

However, according to this Apple Support page for the multiport adapter I am using (model A2119), only 2020 13-inch models can output at 60 hz with it. https://support.apple.com/en-us/HT207806

Lose the adapter. There is never a reason to use HDMI for a computer monitor unless you have absolutely no alternative.

 

[dvm258]

Yes, this. The MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports) just has an Intel GPU which only supports DisplayPort 1.2 (it has no DisplayPort 1.4, DSC, or 4:2:0).

The Apple USB-C Digital AV Multiport Adapter is like a USB-C Hub. USB-C has four high speed lines. The hub uses two of them for USB 3.0 (one for transmit and another for receive), leaving only two lines for DisplayPort lanes.

Two lanes of DisplayPort 1.2 can only do 4K 30Hz (8bpc RGB HDMI, 10bpc RGB not HDMI, 10bpc 4:2:2 HDMI). DisplayPort 1.2 doesn't support DSC or 4:2:0 so it cannot do 4K 60Hz using those methods. You need four lanes of DisplayPort 1.2 to do 4K 60Hz 10bpc RGB. Therefore you need a Thunderbolt dock, or a USB-C hub that does USB at only USB 2.0 speed, or an adapter that doesn't include USB 3.x.

DisplayPort 1.4 has 50% more bandwidth than DisplayPort 1.2, so it can do 4K 60Hz 8bpc RGB with just two lanes but it can't do 8bpc RGB HDMI 2.0 timing, or 10bpc RGB (required for HDR). To do 4K 60Hz 10bpc with two lanes of DisplayPort 1.4 requires DSC or 4:2:2 or 4:2:0. Apple's adapter supports DisplayPort 1.4 and DSC on the input (DSC works in Catalina but may be gone in Big Sur?)

Thanks for the explanation! I currently have a DisplayPort to USB-C/Thunderbolt 3 cable in the mail to me I can plug directly into my MacBook Pro with no adapter. If I'm following correctly, I believe that will work?

 

[Amethyst1]

If I'm following correctly, I believe that will work?

Yes.

 

[joevt]

Thanks for the explanation! I currently have a DisplayPort to USB-C/Thunderbolt 3 cable in the mail to me I can plug directly into my MacBook Pro with no adapter. If I'm following correctly, I believe that will work?

You didn't say what display you have. You did imply that it has a DisplayPort input (I think I missed that detail). Definitely use that. DisplayPort 1.2 has more bandwidth (720MHz 8bpc) than HDMI 2.0 (600MHz 8bpc) so you don't have to worry about using 8bpc or 4:2:2. DisplayPort 1.2 will do 10bpc RGB just fine at 4K 60Hz (as long as the display is not using HDMI 2.0 timing 594MHz - it will probably use something like CVT-RB timing 533MHz which is low enough to get under the DisplayPort 1.2 10bpc max of 576MHz).

 

[tzxsean]

Yes, this. The MacBook Pro (13-inch, 2018, Four Thunderbolt 3 ports) just has an Intel GPU which only supports DisplayPort 1.2 (it has no DisplayPort 1.4, DSC, or 4:2:0).

The Apple USB-C Digital AV Multiport Adapter is like a USB-C Hub. USB-C has four high speed lines. The hub uses two of them for USB 3.0 (one for transmit and another for receive), leaving only two lines for DisplayPort lanes.

Two lanes of DisplayPort 1.2 can only do 4K 30Hz (8bpc RGB HDMI, 10bpc RGB not HDMI, 10bpc 4:2:2 HDMI). DisplayPort 1.2 doesn't support DSC or 4:2:0 so it cannot do 4K 60Hz using those methods. You need four lanes of DisplayPort 1.2 to do 4K 60Hz 10bpc RGB. Therefore you need a Thunderbolt dock, or a USB-C hub that does USB at only USB 2.0 speed, or an adapter that doesn't include USB 3.x.

DisplayPort 1.4 has 50% more bandwidth than DisplayPort 1.2, so it can do 4K 60Hz 8bpc RGB with just two lanes but it can't do 8bpc RGB HDMI 2.0 timing, or 10bpc RGB (required for HDR). To do 4K 60Hz 10bpc with two lanes of DisplayPort 1.4 requires DSC or 4:2:2 or 4:2:0. Apple's adapter supports DisplayPort 1.4 and DSC on the input (DSC works in Catalina but may be gone in Big Sur?)

Hey sorry to reply to old thread,

Would a Type C to Type C cable (with USB 4.0 capability + 100W PD) be able to support 4k @ 60Hz while enabling high bandwidth for USB 3.0 devices as well? or I really need to get a Type C to DisplayPort cable?

Current laptop: 2019 13" MBP
Current monitor: Dell S2722QC

 

[joevt]

Would a Type C to Type C cable (with USB 4.0 capability + 100W PD) be able to support 4k @ 60Hz while enabling high bandwidth for USB 3.0 devices as well? or I really need to get a Type C to DisplayPort cable?

Current laptop: 2019 13" MBP
Current monitor: Dell S2722QC

MacBook Pro 13 inch 2019 has 8th Generation "Coffee Lake" CPU with iGPU limited to DisplayPort 1.2 HBR2 bandwidth with no DSC support. Therefore you can't get 4K60 and USB 3.x on the same cable unless you use a Thunderbolt dock or hub. In that case, the Thunderbolt cable has DisplayPort and USB tunnelled using Thunderbolt. Thunderbolt has 40Gbps bandwidth so it can transmit two HBR2 x4 connections (up to 17.28 Gbps each) (4K60 requires at most 16 Gbps) while still having enough bandwidth for USB 3.x.

You can get USB-C docks (from Cable Matters) that provide only USB 2.0 so that the DisplayPort connection can have max bandwidth. It will be limited to one DisplayPort connection (up to 17.28 Gbps for HBR2) plus one USB connection up to 480 Mb/s (which is less than 60 MB/s).

Actually, since the Dell S2722QC has a USB-C port, it is basically a USB-C dock. It's a special kind of USB-C dock that has a switch called "USB-C prioritization"). As explained in the user guide (which you can download), this USB-C prioritization switch "allows you to specify the priority to transfer the data with high resolution (High Resolution) or high speed (High Data Speed) when using the USB Type-C port. If the current platform is DP 1.4 (HBR3), use High Data Speed to access full video performance with high data speed. If the current platform is DP 1.2 (HBR2) or below, select High Resolution for accessing full video performance with data and network speed drop."

High Resolution means four lanes of DisplayPort + USB 2.0.
High Data Speed means two lanes of DisplayPort + USB 3.0.

Since your Mac only supports DisplayPort 1.2 HBR2 link rate, you need four lanes to achieve 4K60 10bpc RGB.
If you had a Mac that supported DisplayPort 1.4 HBR3 link rate, you could use two lanes of DisplayPort to achieve 4K60 8bpc and USB 3.0. If you need 10bpc, then you would need to use 4:2:0 chroma sub sampling or a lower refresh rate.

With the limitation of USB-C even with HBR3 link rate, I would prefer using DisplayPort input with seperate USB 3.0 connection. But if you're just going to connect a mouse and keyboard to the display, then the USB-C connection with USB-C prioritization set to "High Resolution" may be preferable.

 

[tzxsean]

MacBook Pro 13 inch 2019 has 8th Generation "Coffee Lake" CPU with iGPU limited to DisplayPort 1.2 HBR2 bandwidth with no DSC support. Therefore you can't get 4K60 and USB 3.x on the same cable unless you use a Thunderbolt dock or hub. In that case, the Thunderbolt cable has DisplayPort and USB tunnelled using Thunderbolt. Thunderbolt has 40Gbps bandwidth so it can transmit two HBR2 x4 connections (up to 17.28 Gbps each) (4K60 requires at most 16 Gbps) while still having enough bandwidth for USB 3.x.

You can get USB-C docks (from Cable Matters) that provide only USB 2.0 so that the DisplayPort connection can have max bandwidth. It will be limited to one DisplayPort connection (up to 17.28 Gbps for HBR2) plus one USB connection up to 480 Mb/s (which is less than 60 MB/s).

Actually, since the Dell S2722QC has a USB-C port, it is basically a USB-C dock. It's a special kind of USB-C dock that has a switch called "USB-C prioritization"). As explained in the user guide (which you can download), this USB-C prioritization switch "allows you to specify the priority to transfer the data with high resolution (High Resolution) or high speed (High Data Speed) when using the USB Type-C port. If the current platform is DP 1.4 (HBR3), use High Data Speed to access full video performance with high data speed. If the current platform is DP 1.2 (HBR2) or below, select High Resolution for accessing full video performance with data and network speed drop."

High Resolution means four lanes of DisplayPort + USB 2.0.
High Data Speed means two lanes of DisplayPort + USB 3.0.

Since your Mac only supports DisplayPort 1.2 HBR2 link rate, you need four lanes to achieve 4K60 10bpc RGB.
If you had a Mac that supported DisplayPort 1.4 HBR3 link rate, you could use two lanes of DisplayPort to achieve 4K60 8bpc and USB 3.0. If you need 10bpc, then you would need to use 4:2:0 chroma sub sampling or a lower refresh rate.

With the limitation of USB-C even with HBR3 link rate, I would prefer using DisplayPort input with seperate USB 3.0 connection. But if you're just going to connect a mouse and keyboard to the display, then the USB-C connection with USB-C prioritization set to "High Resolution" may be preferable.

Thanks for the detailed explanation.

In essence, if I'm only connecting mouse and keyboard to the monitor, I can just opt for High Resolution monitor settings (achievable by normal Type C to Type C cable).

Please let me know if my understanding is incorrect.

Thanks again!

 

[joevt]

In essence, if I'm only connecting mouse and keyboard to the monitor, I can just opt for High Resolution monitor settings (achievable by normal Type C to Type C cable).

Yes. You can connect storage devices also, but they will be limited to 60 MB/s which is slightly slower than a 1 Gbps network connection.