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JoseDB

macrumors newbie
Nov 29, 2021
4
3
What Sabrent USBc to HDMI 2.1 device do you mean? Is it some adapter, or a cable? I found this one:


I didn't order a Sabrent, but did order this one:

and then figured Id try this cable in it:

If you have one device that can kind of do it all, I'd be interested to know what it is.
That’s the one.
Full specs here https://www.sabrent.com/product/DA-...r-8k-60hz-4k-120hz-with-dsc-function-da-uch8/

No caveats about Macs be hamstrung etc and Sabrent are a pretty reputable brand (I have some of their other devices like USB-C 5Gbps Ethernet adapter).

The fact it expressly talks about DSC gives me hope.
 

ZombiePhysicist

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May 22, 2014
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I havent tried it. I didnt see anything there about a middle dispalyport conversion, but certainly is interesting. However, wonder if this is somehow better/different than just using a straight HDMI 2.1 port on my Mac Pro video card. It may be a necessary conversion "just because" the drivers on Mac are so not tailored to 8k yet. Might be worth a try.
 

JoseDB

macrumors newbie
Nov 29, 2021
4
3
I'm working on the basis that as Apple's 6K60 display works via DP 1.4 with DSC (Ref https://www.apple.com/pro-display-xdr/pdf/Pro_Display_White_Paper_Feb_2020.pdf) and an 8K60 signal fits in the same bandwidth, so maybe as the transport method is definitely supported by newish Mac's, then just bumping the resolution up that is sent over that supported transport isn't a huge ask. That being compared to native HDMI which Apple have no vested interest in supporting anything other than basic connectivity for business presentations it seems.

Note the adaptor says it requires "DisplayPort Alternate Mode". That plus the fact that HDMI Alt Mode never really got implemented by anyone and only supports up to HDMI v1.4b, so could not carry 8K60. So it has to do DP Alt Mode 1.4/DSC and then convert to HDMI 2.1 in the adaptor rather than HDMI Alt Mode 1.4b all the way through.

I've got a QE75QN900A in the lounge so I think I'll order the adaptor as it's cheap enough to take a risk on. If it works then I can select a TV for my office setup.
 
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Arvine

macrumors member
Dec 15, 2017
39
25
I wonder, do you think if the tv had a DisplayPort 1.4 port, would the 8k image come through? And if so, doesn’t that mean the real issue is finding some cable/adapter that can push the right timings through. Although I’m confused why a straight hdmi 2.1 cable with 2.1 ports on both sides wouldn’t work. ?
There is a guy here on the forum that said he got 8K@30hz over Displayport 1.4, hooking up the Dell 32" 8K monitor. So that means a TV with native Displayport could work in theory. I dont remember what hardware he had. There are very few TVs with Displayport, and they dont yet have 8K as far as I know. Only 4K. As explained before, I tried with a Displayport to HDMI 2.1 adapter and that didnt work with the AMD 6800.

There seams to be an issue with HDMI 2.1 on macOS or some of the graphics drivers. I would guess HDMI 2.1 is not yet supported. Also unclear if DSC is supported.

All in all, I dont see a solution for the moment to get 8K on a a large 8K TV using MacOS.
 
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JoseDB

macrumors newbie
Nov 29, 2021
4
3
Yep, 8K30 over DP 1.4 is known to work with MacOS.

Stacking adaptors rarely works. It may have been the combo didn't support DSC (a likely scenario IMO) which would definitely not have helped.

If I can 8K30 with 2xHiDPI I'll live with it. 8K60 would be nice though :)
 
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Arvine

macrumors member
Dec 15, 2017
39
25
So I just ordered an 85" 8k display, so now I'm really motivated to make this work!

In searching around I came on to this post:

This is a year old post. What I guess is that he also got a scaled down 8K to 4K signal to the TV, just like I get. The Mac itself reports 8K using e.g. SwitchResX) but the image is really just a 4K image with 8K text size. It doesnt look good.

It still makes sense to try the Cable Matters adapter. I tried Club 3D DP 1.4 to HDMI 2.1 CAC 1085. It does owkr, but as I described over. The MAD sends only a 4K signal even if the desktop is 8K. I suspect that the AMD driver or MacOS recognises that there is a HDMI display connected via DP 1.4, and therefore doesnt accept even 8k@30hz.

I consider trying the Cable Matter DP 1.4 to HDMI 2.1 adapter. Maybe it works differently that the Club 3D one.
 
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Arvine

macrumors member
Dec 15, 2017
39
25
AnandTech has a writeup about the Realtek RTD2173 chip used in that Sabrent adapter.

The Realtek chip uses DSC 1.2 to enable 8K@60Hz from DP1.4.
I think the Club 3D CAC 1085 active adapter is using the Realtek chip. I have tried this, I'm not getting 8K using the adapter from the Mac with AMD 6800. Only 4K signal although the desktop is 8K.
 

Arvine

macrumors member
Dec 15, 2017
39
25
Yep, 8K30 over DP 1.4 is known to work with MacOS.

Yes I read that someone got 8K@30hz on the Dell 32 inch 8K monitor using only a single DP cable. I.e. no HDMI 2.1 involved nor DSC. Curious what version of MacOS and what graphics chip was used.
 
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Arvine

macrumors member
Dec 15, 2017
39
25
AnandTech has a writeup about the Realtek RTD2173 chip used in that Sabrent adapter.

The Realtek chip uses DSC 1.2 to enable 8K@60Hz from DP1.4.
They also discuss DP 1.4 / HDMI 2.1 adapters at this thread: Mac mini: 4k @ 120hz?
 

Arvine

macrumors member
Dec 15, 2017
39
25
"MacOS incorrectly limiting pixel clock to 600mhz on Display Port 1.4 to HDMI 2.1 adapters, preventing 4k120"

Here is the post about a possible limitation with MacOS.
 
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ZombiePhysicist

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May 22, 2014
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"MacOS incorrectly limiting pixel clock to 600mhz on Display Port 1.4 to HDMI 2.1 adapters, preventing 4k120"

Here is the post about a possible limitation with MacOS.

interesting. I know generally stacking adapters messes things up, but here, there is a tiny chance it could help. The reporting of the 60o hz clock makes Mac OS work wrong, I wonder if one of the links fails to report that correctly somehow, would it “trick” the connection to work? It will likely fail but worth a shot to try it.
 
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ZombiePhysicist

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Original poster
May 22, 2014
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That's me.

I'm currently using Catalina (10.15.7) and using the Radeon Vega Frontier Edition (16GB HBM).
So this card:

It has 3 DisplayPort 1.4 and one hdmi 2.0 ports if I read it correctly.

can you tell us:

1 what port you’re using on the card,
2 what cables you’re using to connect to the display,
3 and what port on the display you’re connecting to?

thanks so much.
 

joevt

Contributor
Jun 21, 2012
6,689
4,085
So this card:

It has 3 DisplayPort 1.4 and one hdmi 2.0 ports if I read it correctly.

can you tell us:

1 what port you’re using on the card,
2 what cables you’re using to connect to the display,
3 and what port on the display you’re connecting to?

thanks so much.
There's not a lot of options. The answers are probably:
1: DisplayPort 1.4 output
2: DisplayPort 1.4 cable
3: DisplayPort 1.4 input

The Vega doesn't support DSC. The Dell UP3218K doesn't support DSC input.
 

ZombiePhysicist

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May 22, 2014
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There's not a lot of options. The answers are probably:
1: DisplayPort 1.4 output
2: DisplayPort 1.4 cable
3: DisplayPort 1.4 input

The Vega doesn't support DSC. The Dell UP3218K doesn't support DSC input.

Thanks that helps. It looks like macOS is pretty cool with a pure DisplayPort setup, and a ****show with HDMI2.1. :/

Isnt there some mode, even via HDMI2.0 that gives you 8k? Is it like 8k@30hz maybe with some kind of compression or lowered subsampling? I know DSC doesnt work with HDMI2.0 but maybe there is some lowered settings that get you to at least 8k@30 over the supported HDMI2.0?

Yes, but only if you give up on chroma subsampling 4:4:4. 4:2:0 should be able to do 4k120 at the cost of a worse image quality.

I may be wrong, but I think 4k@120 takes up roughly the same bandwidth as 8k@30.
 
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joevt

Contributor
Jun 21, 2012
6,689
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4:2:0 8bpc is basically 12bpp (4:2:0 is 12 components per 8 pixels which normally has 24 components)
With the bandwidth of HDMI 2.0, that's enough to get 4K120 or 8K30. You just need an OS driver, GPU, and display that will support it.
 

ZombiePhysicist

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May 22, 2014
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Pressure

macrumors 603
May 30, 2006
5,076
1,407
Denmark
So this card:

It has 3 DisplayPort 1.4 and one hdmi 2.0 ports if I read it correctly.

can you tell us:

1 what port you’re using on the card,
2 what cables you’re using to connect to the display,
3 and what port on the display you’re connecting to?

thanks so much.
It's a pure DP1.4 setup, as @joevt mentions above. It doesn't matter what DP1.4 input or output I pick on the graphic card or monitor. Single cable DP 1.4 will display 8K@30Hz.
BTW I think you ran scripts to get you setup to work? This might be helpful:

It's working fine now at 8K@60Hz using both DP 1.4 cables and enabling HiDPI with a script.
 
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Pressure

macrumors 603
May 30, 2006
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Is it treating the display as a single display, or is it acting like two portrait displays, with a menu on only one of them?
It's treating it as two 3840x4320 displays (1920x2160 HiDPI) so the top menu is only on half the screen but I use auto-hide on it.

It baffles me that Apple just doesn't care more about monitor support. It seems like an easy fix.

The alternative is 8K@30Hz with a single cable.
 
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Amethyst1

macrumors G3
Oct 28, 2015
9,366
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It baffles me that Apple just doesn't care more about monitor support. It seems like an easy fix.
They definitely know the UP3218K exists because they’ve added a pointless override file for it (I apologise if this is old news to you). I guess they want people to get the XDR instead.
 

ZombiePhysicist

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May 22, 2014
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XDR is overpriced crap. But you may well be right. It’s perplexing how resistant they are to 8k for a while now.
 
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