Why the heck I can't tell a difference between ULMB2 on vs off at 540Hz ???

[fresha]

I got me a PG248QP and overclocked it to 540Hz then turned on ULMB2 and for some reason the image brightness is the only thing that changes, the image looks literally the same lol... I tried tracking a moving image against static elements and its the same, can't tell a difference!

Is it maybe because I am strobing at 540Hz and because unstrobed 540Hz just looks so clear already, that maybe the human eye can't see a difference, or is the difference noticeable but maybe I have some third variable?

I have tried:

1. match Hz to FPS

2. playing around with pulse width

3. doing various tests like this one https://www.testufo.com/map#pps=960&pur ... llscreen=1 and the image just looks like the same....

4. NVCP settings is obviously gsync turned off and monitor set to fixed refresh rate (nvidia removed ULMB option in control panel so I just keep it on in OSD)

I have not tried

1. reinstalling my graphics drivers

2. Any other ULMB2 monitors

3. DP cable that came with the monitor (don't think its DP cable issue as my current one does 540Hz no issues...)

Could it maybe be a hardware issue that the monitor shows ULMB2 is on and brightness dims a bit and changes with adjusting pulsewidth YET their is no strobing going on? (Anyone heard of something like this?)

Its either that or strobing 540Hz is useless since 540Hz is already pretty clear by itself

[patryk92 · Accepted solution]

I've been playing around with my PG27AQN and for some reason I can't see much difference between 360Hz ULMB 2 ON and OFF either. If I go down to 240 or 144Hz I can clearly see the difference. So here's my opinion:
The root cause is DSC. The compression rate increases at higher refresh rates and this makes ULMB 2 look worse.
Turn DSC off and tell me if you can now see the difference between ULMB 2 ON/OFF. If so, I'm right.

Oh, and by the way, I would recommend this test as the difference and fine-tuning is much easier:
https://www.testufo.com/crosstalk#pps=2560&photo=alien-invasion.png&area=full&pursuit=0&fullscreen=1

[fresha]

Dude you might be right!

I turned off DSC and max Hz was 360 for this monitor and now I can finally tell a clear difference

Will do some more blurbuster tests to 100% confirm but it seems your right!

So at the momment, its either 1440p 240hz ulmb2 or 1080p 360hz ulmb2, cant go higher without dsc right?

AMD has a DP 2.1 on their 7000 cards now just need these dyac/ulmb monitors to get DP 2.1 ports

[patryk92]

There are some other issues with AMD. As far as I know, there is no way to turn off VRR, so you can't even use ULMB 2 with an AMD graphics card. DP 2.1 is what we absolutely need in our monitors.
Yes, that's right, 1080p 360 Hz is the maximum you can get without any DSC stuff as that's the limit of DP 1.4.

Hey Asus, how much does it cost to send back my $1.3k monitor so you can add a DP 2.1 port to it? (I'm not kidding)

[patryk92]

I have an update and may have found the real solution!

The color space affects the ability to display ULMB 2 correctly, this again has something to do with compression. When I use the standard RGB color space, ULMB 2 appears washed out at 360Hz. However, everything looks fine in the YCbCr 4:4:4 color space.

I would be very interested to know if you also notice an improvement on your PG248QP at full refresh rate and the YCbCr 4:4:4 color space. If so, I would say that when using DSC, choosing the YCbCr 4:4:4 color space is always best.

Best regards