DSC and alt-tab bug on XG27AQMR and other displays

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nrb
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Joined: 26 Sep 2023, 09:44

DSC and alt-tab bug on XG27AQMR and other displays

Post by nrb » 06 Dec 2023, 18:10

Hello,
As far as I understand refresh rates > 240hz at 1440p on displays such as the Asus XG27AQMR
are attainable with DSC. Apparently because of a bug in the Nvidia driver, there seems to be an
issue with alt-tabbing causing a black-screen for a few seconds. Has this bug already been fixed?
Also, is it possible to run the display at its fullest potential without DSC, and are there any issues on AMD cards?

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r0ach
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by r0ach » 07 Dec 2023, 06:53

nrb wrote:
06 Dec 2023, 18:10
Hello,
As far as I understand refresh rates > 240hz at 1440p on displays such as the Asus XG27AQMR
are attainable with DSC. Apparently because of a bug in the Nvidia driver, there seems to be an
issue with alt-tabbing causing a black-screen for a few seconds. Has this bug already been fixed?
Also, is it possible to run the display at its fullest potential without DSC, and are there any issues on AMD cards?
I have an XG27AQMR coming in tomorrow and run a 7800xt. Also, I find Nvidia drivers totally unusable now latency-wise which is why I switched. Maybe they react differently on newer cards, but new Nvidia drivers on a 1070 GTX were abysmal. With AMD it seems I don't even have to cherry pick drivers and can just take the newest one and then remove all the bloat from it via AMD driver slimmer and get decent results.

nrb
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Joined: 26 Sep 2023, 09:44

Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by nrb » 07 Dec 2023, 08:05

r0ach wrote:
07 Dec 2023, 06:53
I have an XG27AQMR coming in tomorrow and run a 7800xt. Also, I find Nvidia drivers totally unusable now latency-wise which is why I switched. Maybe they react differently on newer cards, but new Nvidia drivers on a 1070 GTX were abysmal. With AMD it seems I don't even have to cherry pick drivers and can just take the newest one and then remove all the bloat from it via AMD driver slimmer and get decent results.
Please report if you have any alt-tab issue, if DSC is required after all, etc.
That would be very helpful to me in making upcoming purchase decisions.

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r0ach
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by r0ach » 07 Dec 2023, 09:47

edit: review below
Last edited by r0ach on 09 Dec 2023, 16:36, edited 1 time in total.

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r0ach
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by r0ach » 09 Dec 2023, 16:18

After using the monitor:

- If you're one of those people who doesn't like how the cursor feels with freesync turned on, DSC is similar/worse. Just sort of abnormal or stiffer cursor movement.

- 300hz works with DSC off but it's YCBCR 422

- 300hz with DSC on is 10bit RGB (probably with dithering aka not something I even want)

- 240hz mode is 8bit RGB but doesn't feel as good as a normal 240hz native monitor (insert whatever theory about non-native refresh here). The Koorui 1440p 240hz IPS panel feels like it controls a lot better (albeit with pretty annoying eyestrain effects) at 240hz.

- With DSC on I think I noticed it changing games to bordered window mode (not borderless) when I alt-tabbed

- Only spent one day with the monitor but think eye strain was probably higher on 300hz 10 bit mode (dithering?) than 240hz 8 bit. I’ve never been bothered by 6+2bit TN panel dithering so not sure why 8+2 would be worse.

TLDR: I don't like DSC monitors and prefer just plain 240hz 1440p better
Last edited by r0ach on 21 Dec 2023, 17:04, edited 2 times in total.

MalcolmPurdy
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by MalcolmPurdy » 18 Dec 2023, 02:20

r0ach wrote:
09 Dec 2023, 16:18
After using the monitor:

- If you're one of those people who doesn't like how the cursor feels with freesync turned on, DSC is similar/worse. Just sort of abnormal or stiffer cursor movement.

- 300hz works with DSC off but it's YCBCR 422 (I run AMD with minimal install for latency reasons so I don't have control over what color format it's feeding Windows but not enough bandwidth for regular RGB so this is what it gives you)

- 300hz with DSC on is 10bit RGB (probably with dithering aka not something I even want)

- 240hz mode is 8bit RGB but doesn't feel as good as a normal 240hz native monitor (insert whatever theory about non-native refresh here). The Koorui 1440p 240hz IPS panel feels like it controls a lot better (albeit with pretty annoying eyestrain effects) at 240hz.

- With DSC on I think I noticed it changing games to bordered window mode (not borderless) when I alt-tabbed

- Only spent one day with the monitor but think eye strain was probably higher on 300hz 10 bit mode (dithering?) than 240hz 8 bit. I’ve never been bothered by 6+2bit TN panel dithering so not sure why 8+2 would be worse.

TLDR: I don't like DSC monitors and prefer just plain 240hz 1440p better
Thanks for the review, I will keep it in my mind. I appreciate your effort.

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r0ach
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by r0ach » 21 Dec 2023, 17:15

MalcolmPurdy wrote:
18 Dec 2023, 02:20
Thanks for the review, I will keep it in my mind. I appreciate your effort.
If you were wondering about other panels, I think LG’s new 1440p 240hz that uses a BOE panel instead of their own has DSC forced on with no way to turn it off while running at 240hz 10 bit by default. If people were curious if they notice a difference in DSC being on or off, at least the Asus model allows you to toggle it in the menu. It’s possible DSC turns off on the LG if you force it to 8 bit instead, but I have no idea.

Detrizor
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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by Detrizor » 22 Dec 2023, 10:29

In case you're still interested, I'm running G42P5 monitor (4k 138 hz), if it connected to Nvidia GPU (3080 ti) I have his terrible black screen problem when alt-tabing from game (but not when returning to it), so this bug hasn't been fixed. If I connect monitor to AMD GPU (7900 XTX) then there is no problems with alt-tabing at all, it's instant. Funny thing that this bug with DSC on Nvidia has been known already a year ago, if not more, and still isn't fixed. But it is broadly believed that AMD drivers are "buggy", yeah.

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Re: DSC and alt-tab bug on XG27AQMR and other displays

Post by Chief Blur Buster » 23 Dec 2023, 04:08

Putting permalink for visiting manufacturer reps to read:

DSC Rabbit Hole and Bugs in early DSC implementations

Properly done DSC should be literally lagless (<0.1ms!) but we're not there yet. Often the video port transceiver chips (that don't have native DSC directly at the port) just lazily doff it to some downstream chip, or other sheningians/workarounds. Hopefully newer video port transceivers get the DSC act together more consistently!

(Yes, *some* of the manufacturers lurks these forums, to monitor(pun) for issues)
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