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Flow91

macrumors newbie
Original poster
Dec 10, 2015
23
6
Hi,

I'm thinking about buying an LG OLED tv (CX or C9) that runs on 4k and 120 hz. I'd also like to hook up a MacOS system, but until now they wouldn't be able to make use of the display's possibilities. Now as the M1 Mac mini has been presented I wonder if it runs 4k at 120 hz smoothly.

I know that the Mac only supports HDMI 2.0, but there are adapters for transforming DisplayPort 1.4 to HDMI 2.1. What do you think, will it run? Or would an older Intel Mac with an eGPU a better solution?

Have you made good experiences with adapters for transforming DisplayPort to HDMI 2.1 signals?
 
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saulinpa

macrumors 65816
Jun 15, 2008
1,117
555
I'm thinking 120 Hz won't be supported natively but maybe something like SwitchResX will be able to tweak it.

Apple states that the M1 supports the 6K monitor so should have similar performance. 4K@120 is 26gb/s vs 6K@60 which is 31gb/s.
 

bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
I have a CX so I'll let you know what happens, but I'm not expecting "smooth" 4K @ 120Hz.

Bandwidth-wise, it should be enough. Realistically, I don't think Apple is going to give support to the M1. Maybe the M1X or M2 will be able to do that.

Also, I can't fathom using the CX as a computer monitor, to be honest. Auto Brightness Limiter (ABL) is very aggressive on white screens. That and there's the risk of image retention.
 
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Flow91

macrumors newbie
Original poster
Dec 10, 2015
23
6
Thank you very much for your replies! So Bill-P, you are planning to buy an M1 Mac? If yes and you try it on your CX, it would be great if you could let me know what happens and how it runs the screen.
 

yoak

macrumors 68000
Oct 4, 2004
1,597
142
Oslo, Norway
I have a C8, and would love to use it as viewing monitor at time to check my footage before sending it off to clients. One reason I'm tempted by the new mini, almost ordered, but will wait for some reviews. Not in that much of a hurry after they are starting to close everything down again
EDITI know C8 is only 2.0b
 

bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
Yeah, I have an M1 coming. I already have a Windows computer for work, plus I still have 1 or 2 older Intel Macs in case I miss them.

Just trying to see if M1 will replace my 16" MacBook Pro. It seems like at least it won't be a significant performance downgrade.

Will let you know how it works with CX. My main work monitor is LG 34WK95U. That one supports single DisplayPort 1.4 or dual DisplayPort 1.2 streams. I'm hoping M1 will be able to work with that, but the more extreme test would be to see if DisplayPort 1.4 to HDMI 2.1 will allow it to work with CX. I'm guessing... no, but it doesn't hurt to try.
 

LonestarOne

macrumors 6502a
Sep 13, 2019
722
967
McKinney, TX
Just read the specs.

“One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0.”

120 Hz > 60 Hz. So, no.
 
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joevt

Contributor
Jun 21, 2012
4,090
2,125
Just read the specs.

“One display with up to 6K resolution at 60Hz connected via Thunderbolt and one display with up to 4K resolution at 60Hz connected via HDMI 2.0.”

120 Hz > 60 Hz. So, no.
Refresh rate is not a limiter for GPUs. Pixel clock is.

HDMI 2.0 is limited to 600 MHz pixel clock (8 bpc). HDMI 2.0 4K 60Hz is 594 MHz. More than 8 bpc requires chroma sub sampling.

Normally, DisplayPort 1.4 is limited to 864 MHz for 10bpc and 1080 MHz for 8bpc (actual numbers are less because of overhead). DSC can effectively triple that to allow 8K 60Hz (2376 MHz).

HDMI 2.1 is limited to 1422 MHz 10bpc without DSC (DSC can be used by HDMI 2.1 to triple that).

5K 60 Hz is ~933 MHz
4K 120Hz is 1188 MHz (HDMI)
6K 60Hz is 1286 MHz (uses DSC)
8K 60Hz is 2376 MHz (HDMI)
8K 120Hz is 4752 MHz (HDMI) (4258 MHz using CVT-RB2 timing)

The Club-3d DisplayPort 1.4 to HDMI 2.1 4K 120Hz adapter uses DSC.
 

Flow91

macrumors newbie
Original poster
Dec 10, 2015
23
6
Thanks for your detailed explanation!

So if I understand that correctly, there is a chance that it might run by using the Club-3d CAC-1085 adapter? I'm sorry for asking, but what is DSC? I couldn't find an explanation on that.
 

joevt

Contributor
Jun 21, 2012
4,090
2,125
Thanks for your detailed explanation!

So if I understand that correctly, there is a chance that it might run by using the Club-3d CAC-1085 adapter? I'm sorry for asking, but what is DSC? I couldn't find an explanation on that.
Yes, there's a chance the CAC-1085 will work for a HDMI 2.1 TV connected to a M1 Mac mini.

DSC - Display Stream Compression. Used in DisplayPort 1.4 and HDMI 2.0. It's a visually lossless compression algorithm for displays (approximately 3:1 compression ratio). It is different than a compression algorithm that you would use for video which would have a much greater compression ratio.

 
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Weasel128

macrumors newbie
Nov 20, 2020
2
0
Hello! Did someone test the connection to a LG CX48? Looking forward to an solution so I can connect my MacBook m1 to 4K 120hz!
 

bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
Well, just tried my M1 MacBook Pro with CX 55". No dice. Limited to 4K 60Hz still.

Maybe I can try a different adapter? But as far as I can see, it may be because DisplayPort 1.4 implementation in M1 is incomplete. My LG 34WK95U also doesn't work in DisplayPort 1.4 mode... (but it works fine with DisplayPort 1.2)
 

joevt

Contributor
Jun 21, 2012
4,090
2,125
Well, just tried my M1 MacBook Pro with CX 55". No dice. Limited to 4K 60Hz still.

Maybe I can try a different adapter? But as far as I can see, it may be because DisplayPort 1.4 implementation in M1 is incomplete. My LG 34WK95U also doesn't work in DisplayPort 1.4 mode... (but it works fine with DisplayPort 1.2)
That would be messed up if HBR3 weren't supported.

Try SwitchResX? Don't know if it works on M1.

Option click "Scaled" in Displays preferences panel to see more options?

What adapter are you using?
 

bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
This one:

Tried SwitchResX, and it doesn't seem to work right (if at all?). "Scaled" doesn't show anything special. I don't know if HBR3 is supported. Likely it's just HBR2.

If HBR3 was supported, I'd think the LG 34WK95U should work with DisplayPort 1.4. Someone else also has the same monitor and couldn't get DP1.4 with his M1 Mac either.
 

Ninja Dom

macrumors 6502a
Feb 12, 2007
625
123
A person on another forum used THIS SPECIFIC cable and got 1080p @ 120HZ on his M1 Air.

Cable Matters USB C to DisplayPort Cable (USB-C to DisplayPort 1.4 Cable/USB C to DP Cable) support 8K@60Hz, 4K@60Hz, 2K@144Hz in Black 1.8m - Thunderbolt 3 Port Compatible for MacBook Pro, Dell XPS


I’m hoping that it’ll also do 1440p @ 120Hz on the M1 Mac Mini too. I’ve got a 165Hz 1440p monitor.

8456D9F5-0022-4994-B387-B3F2E2BB549C.png
 
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joevt

Contributor
Jun 21, 2012
4,090
2,125
This one:

Tried SwitchResX, and it doesn't seem to work right (if at all?). "Scaled" doesn't show anything special. I don't know if HBR3 is supported. Likely it's just HBR2.

If HBR3 was supported, I'd think the LG 34WK95U should work with DisplayPort 1.4. Someone else also has the same monitor and couldn't get DP1.4 with his M1 Mac either.
Ok. At least the adapter provides a picture. That's a starting point.

I haven't seen anyone get much info from the log stream command yet, but I guess we can try this:
Code:
log stream --style compact --info --debug --predicate 'message matches ".*[^0-9][0-9]{3,4} *x *[0-9]{3,4}[^0-9].*"'
Then disconnect the display, press command-K to clear the terminal window, reconnect the display. When the image appears, select all and copy to a new text file.

A person on another forum used THIS SPECIFIC cable and got 1080p @ 120HZ on his M1 Air.

Cable Matters USB C to DisplayPort Cable (USB-C to DisplayPort 1.4 Cable/USB C to DP Cable) support 8K@60Hz, 4K@60Hz, 2K@144Hz in Black 1.8m - Thunderbolt 3 Port Compatible for MacBook Pro, Dell XPS


I’m hoping that it’ll also do 1440p @ 120Hz on the M1 Mac Mini too. I’ve got a 165Hz 1440p monitor.
1080p120 is only half the bandwidth of 4K60 and therefore only requires a DisplayPort 1.2 cable (HBR2).

For HBR3 testing we need a resolution/refresh rate greater than 1080p240, 1440p120, or 4K60
such as 1440p144 or 4K120 or 5K60 or 8K30.
 
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dmccloud

macrumors 68000
Sep 7, 2009
1,935
789
Anchorage, AK
I know that on the DTK, an Insignia USB-C to DisplayPort cable will easily run 1080p at 144Hz. I do not have access to a DTK connected to a 1440p or 4k monitor to test just how far the refresh rate can be pushed, so I can't speak to how well either the DTK or M1 machines could handle higher framerates at those resolutions.
 
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bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
I can't find my Thunderbolt 3 > DisplayPort 1.4 adapter anywhere. Tried looking up and down the house. Ordered a new one Amazon, but it won't come until Monday or Tuesday. Sorry for the delay, @joevt.

In the mean time, @matthoffner, can you please run the script above for joevt and see what the output is? I'm curious as well.

Also, yeah, I was only able to get 1440p @ 120Hz working with LG CX. 4K could only do 60Hz.
 

matthoffner

macrumors newbie
Mar 4, 2014
20
16
I can't find my Thunderbolt 3 > DisplayPort 1.4 adapter anywhere. Tried looking up and down the house. Ordered a new one Amazon, but it won't come until Monday or Tuesday. Sorry for the delay, @joevt.

In the mean time, @matthoffner, can you please run the script above for joevt and see what the output is? I'm curious as well.

Also, yeah, I was only able to get 1440p @ 120Hz working with LG CX. 4K could only do 60Hz.

Attached from running with hdmi cable and with dp to hdmi 2.1 cable.
 

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Ninja Dom

macrumors 6502a
Feb 12, 2007
625
123
When I get my M1 Mac Mini I’m gonna run 1440p @ 120Hz using the HDMI cable as it frees up a USB-C port.

That’ll be okay, right?
 

Weasel128

macrumors newbie
Nov 20, 2020
2
0
I can't find my Thunderbolt 3 > DisplayPort 1.4 adapter anywhere. Tried looking up and down the house. Ordered a new one Amazon, but it won't come until Monday or Tuesday. Sorry for the delay, @joevt.

In the mean time, @matthoffner, can you please run the script above for joevt and see what the output is? I'm curious as well.

Also, yeah, I was only able to get 1440p @ 120Hz working with LG CX. 4K could only do 60Hz.
What adapters did you use to connect it to the lg cx?
 

bill-p

macrumors 68030
Jul 23, 2011
2,710
1,209
What adapters did you use to connect it to the lg cx?

USB-C > DisplayPort 1.4 (Amazon sells a bunch of these), and then the other adapter I already linked above.

To be honest, I'd actually prefer 4K @ 60Hz here. 120Hz makes images a slight bit cleaner (and amazingly, the M1 can keep up with it with maximum fluidity), but overall, 4K is sharper and clearer than 1440p for texts. And I mostly read static texts.

One thing, though: the CX really sucks with maximum brightness. Auto Brightness Limiter is very aggressive, so brightness jumps up if it's a darker scene, and it scales down significantly when most of the screen is plain white.

That's not to mention brightness has to be adjusted manually via the remote control, and it's buried underneath multiple levels of menu. So I don't think the CX should be used like a computer monitor at all. But maybe that's just me.

In comparison, I have the LG 34WK95U as well. It's meant to be a computer monitor. Brightness adjustment can be achieved very quickly via the control knob, or I can just rely on auto brightness (the display adjusts itself according to ambient, just like the MacBook's screen). CX has no auto brightness.

Last but not least, color calibration is a nightmare on CX. If you already know how to do it, then that's great, but you need to program the TV. By default, the color profile it comes with is not accurate at all. You can switch to one of the TV modes, but that introduces significant lag. In comparison, the LG 34WK95U is 98% DCI-P3, and it's almost a 99% match against my MacBook's screen, versus the iPhone, versus the iPad Pro.

I've seen many Youtube videos of people trying to use the CX 48" as a computer monitor, and absolutely none of them talks about the aggressive ABL, no brightness control, and poor color profile. I do enjoy the CX as a TV, but I'll never want to use it as a computer monitor.
 
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