[Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

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miszt
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[Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

Post by miszt » 15 Mar 2020, 21:16

Hello guys. I'm curious whether there is a big difference between 120hz ulmb and 144hz ulmb.
I'm deciding between two different monitors, which is Asus VG258QR (165hz TN; support 144hz elmb) and Asus VG249Q(144hz ips;supports 120hz elmb).
If there's no siginificant difference between ulmb between 120hz and 144hz, then I'll just go for the 144 ips panel.

Here's the reason for this.
As the blurbuster's law says that
1. As long as fps follows up the refresh rate (I have ryzen3600 and RTX2070super, enough to keep stable 120hz at most of games so it's OK)
2. As long as average gtg doesn't go over the MPRT (120hz mprt 8.33ms, 144hz mprt 6.94ms)
>> Motion blur won't be a problem for both 120hz and 144hz.
Since IPS gaming monitors nowadays have average GTG under 8.33ms, I think ips panel would show a great performance.

If 120hz ulmb and 144hz ulmb doesn't have a big difference, I would just go for IPS since it has better colors and can be used for other tasks.

So...anybody who used ulmb at both refreshrates? Would be a great help to me :)

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Chief Blur Buster
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Re: 120hz ulmb vs 144hz ulmb. Is there a big difference?

Post by Chief Blur Buster » 21 Mar 2020, 20:52

Deends, but usually very tiny difference.

With perfect zero strobe crosstalk, 120fps@120Hz looks almost identical to 144fps@144Hz strobed.

Usually, higher Hz strobing looks worse because the closer your strobed Hz becomes to max Hz, the more strobe crosstalk appears. Refresh rate headroom below Hz is good for strobe quality. 120Hz strobing on a 240Hz monitor is typically better than 120Hz strobing on a 144Hz monitor or 144Hz strobing on a 144Hz monitor.

That said, the world's best strobed 144Hz is better than the world's worst strobed 120Hz. But even reducing the 144Hz setting to 120Hz on that monitor, also improves strobed quality at that Hz.
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miszt
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Re: 120hz ulmb vs 144hz ulmb. Is there a big difference?

Post by miszt » 22 Mar 2020, 11:23

Thanks for your reply, chief! It'a great help.

However, I'm curious about the phrase that
"Refresh rate headroom below Hz is good for strobe quality. 120Hz strobing on a 240Hz monitor is typically better than 120Hz strobing on a 144Hz monitor or 144Hz strobing on a 144Hz monitor."

Is there any theorical explanation about why this happens??

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[Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

Post by Chief Blur Buster » 23 Mar 2020, 01:46

miszt wrote:
22 Mar 2020, 11:23
Thanks for your reply, chief! It'a great help.

However, I'm curious about the phrase that
"Refresh rate headroom below Hz is good for strobe quality. 120Hz strobing on a 240Hz monitor is typically better than 120Hz strobing on a 144Hz monitor or 144Hz strobing on a 144Hz monitor."

Is there any theorical explanation about why this happens??
It's not theory. It's real science.

Strobe crosstalk.

Image

To improve this, you have to hide more LCD GtG in total darkness between strobe backlight flashes.

You need a bigger ratio of refresh time versus GtG time, to reduce strobe crosstalk.

In other words, cramming GtG into the VBI. (VBI = the Vertical Blanking Interval = the pause between refresh cycles).

View www.blurbusters.com/scanout and www.blurbusters.com/redphosphor and click Play on the high speed videos.

LCDs don't refresh all pixels at the same time. The LCD GtG lags after a pixel begins to refresh. And only one pixel row is refreshed at a time. So in high speed videos, you've got a Star Wars style "fade wipe" effect going from top edge to bottom edge where the new refresh cycle replaces the old refresh cycle.

The art of cramming the GtG into the VBI, is to finish LCD pixel transitions at the bottom edge of the screen BEFORE beginning to refresh the next re

NON-STROBED: This is what a slow LCD screen looks like when refreshing, in super-slow-motion, via 960fps high speed video
phpBB [video]


NON-STROBED: This is what a fast LCD screen looks like when refreshing, in super-slow-motion, via 960fps high speed video
phpBB [video]


STROBED: Now when strobing, one only wants the monitor to flash the backlight when the screen is between sweeps:
phpBB [video]


This is easiest with faster GtG and longer VBIs. Longer VBIs are easier with low refresh rates on high refresh rate panels.

This is much easier at lower refresh rates. At 120Hz refresh rate on a 240Hz panel, it is possible to set things up so that it still scanout the refresh cycle in 1/240sec (complete your refresh sweep in 1/240sec), creating 4.2ms pause between refresh cycles. That 4.2ms pause is enough to hide LCD GtG in the total darkness between strobe backlight flashes, before flashing (for about ~1ms) before begininng a new refresh cycle. So full-velocity refresh cycles at lower refresh rates, is what's done.

(That's why Large Vertical Totals used to be popular on older BenQ monitors -- they forced higher-velocity refresh cycles combined with longer pauses between refresh cycles. If you've read stuff like "VT1350", that meant that a screen was spending only 1080/1350ths of a refresh cycle scanning out, with the remainder of the time being a pause between refresh cycles. The larger the VT, the longer the pause between refresh cycles).

So, that's why refresh rate headroom is wonderful for reducing strobe crosstalk. You can max the scanout velocity at the max Hz (e.g. 1/240sec for 240Hz monitors) despite running at a lower refresh rate such as 100Hz. This can either be done at the signal level (Quick Frame Transport / Large Vertical Total) or at the TCON/scaler level (scan-converting an incoming lower horizontal scanrate to a higher horizontal scan rate in number of pixel rows per second).

I milk this intentionally as part of the Blur Busters Approved programme, that's why the XG270 has one of the best IPS strobing at 100Hz and 120Hz refresh rates.
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senny22
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Re: [Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

Post by senny22 » 23 Mar 2020, 04:33

Chief Blur Buster wrote:
23 Mar 2020, 01:46
So, that's why refresh rate headroom is wonderful for reducing strobe crosstalk. You can max the scanout velocity at the max Hz (e.g. 1/240sec for 240Hz monitors) despite running at a lower refresh rate such as 100Hz. This can either be done at the signal level (Quick Frame Transport / Large Vertical Total) or at the TCON/scaler level (scan-converting an incoming lower horizontal scanrate to a higher horizontal scan rate in number of pixel rows per second).
If I want to use a 240hz monitor to strobe at 120hz, do I need to create a custom resolution to benefit from the refresh headroom? (or is it at all beneficial to do so?)

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Re: [Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

Post by Chief Blur Buster » 23 Mar 2020, 16:52

senny22 wrote:
23 Mar 2020, 04:33
If I want to use a 240hz monitor to strobe at 120hz, do I need to create a custom resolution to benefit from the refresh headroom? (or is it at all beneficial to do so?)
For 240Hz ULMB and 240Hz PureXP+, not needed. Those are already doing it automatically and internally.

Some strobed displays, including the Blur Busters Approved ViewSonic XG270, already have internal scan-rate conversion to do max-velocity scanout. These fixed-horizontal-scanrate panels are easier to do higher quality without any advanced user intervention.

Turning on motion blur reduction becomes just an ON/OFF toggle on these displays. Just switch refresh rate to 100Hz or 120Hz.

A custom large VT may be useful for other benefits such as Quick Frame Transport (high scanrate on the cable itself, not just on the panel), assuming the panel is compatible. But may have nasty interactions with panel-based scanrate conversion (in the TCON/scaler).
Head of Blur Busters - BlurBusters.com | TestUFO.com | Follow @BlurBusters on Twitter

       To support Blur Busters:
       • Official List of Best Gaming Monitors
       • List of G-SYNC Monitors
       • List of FreeSync Monitors
       • List of Ultrawide Monitors

senny22
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Joined: 03 May 2019, 17:40

Re: [Strobe Crosstalk] 120hz ulmb vs 144hz vs 240hz. Is there a big difference?

Post by senny22 » 24 Mar 2020, 02:53

Chief Blur Buster wrote:
23 Mar 2020, 16:52
senny22 wrote:
23 Mar 2020, 04:33
If I want to use a 240hz monitor to strobe at 120hz, do I need to create a custom resolution to benefit from the refresh headroom? (or is it at all beneficial to do so?)
For 240Hz ULMB and 240Hz PureXP+, not needed. Those are already doing it automatically and internally.

Some strobed displays, including the Blur Busters Approved ViewSonic XG270, already have internal scan-rate conversion to do max-velocity scanout. These fixed-horizontal-scanrate panels are easier to do higher quality without any advanced user intervention.

Turning on motion blur reduction becomes just an ON/OFF toggle on these displays. Just switch refresh rate to 100Hz or 120Hz.

A custom large VT may be useful for other benefits such as Quick Frame Transport (high scanrate on the cable itself, not just on the panel), assuming the panel is compatible. But may have nasty interactions with panel-based scanrate conversion (in the TCON/scaler).
Cheers, I don't have ULMB / PureXP though as I have the Acer Nitro XF252QX. Any idea about this monitor? If I should use a custom resolution, what settings should I change in CRU?

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