LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction, Freesync

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Chief Blur Buster
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by Chief Blur Buster » 30 Jan 2018, 13:34

VT1302 at 240Hz works? That's the first time I've seen Large VT's be used at 240Hz.

Maybe LG intentionally used Large Vertical Totals in their EDID. That's a first!

Large VT in EDID?
Did you configure 640MHz, or was this automatically done by the monitor? That means it was embedded in its EDID (the plug and play feature where monitor tells the computer what video signal timings it supports). What does ToastyX say for LG's default 144Hz and 120Hz? I'd love to know if they embedded Large Vertical Totals in EDID -- that would be a QFD trick (Quick Frame Delivery) that can reduce the input lag of FreeSync further as well as VSYNC OFF. Could you screenshot the ToastyX screens for 144Hz and 120Hz EDID?

Large VT at max Hz means overclocking headroom
Have you tried overclocking? Large VT capability at max Hz means overclocking headroom, too!
This suggests potentially a (1300/1080)x overclocking factor available -- over 280Hz refresh rate at Reduced Blanking. Have you tried 250Hz?

Reducing strobe crosstalk more: VT1300 at 240Hz means VT2600 at 120Hz
With these numbers, you might be able to achieve ~VT2600 at 120Hz -- almost 5 millisecond VBI idle pausing between very fast-scanned-out 120Hz refresh cycles (math: (1/120sec * ((2600-1080)/2600))). That's a big window for hiding LCD GtG pixel transitions in darkness between refresh cycles between strobe flashes, to reduce strobe crosstalk. This will only work if the panel scanout is synchronous with cable scanout, which is not always true on all LCDs, but is increasingly common on FreeSync-compatible LCDs. The bigger VT, the better for strobe crosstalk.

Reducing Lag: Large VT is also a method of reducing input lag for VRR and VSYNC ON
HDMI 2.1 officializes this as "Quick Frame Delivery" but Large VTs is essentially the same thing, too. It can also reduce input lag of VRR and VSYNC ON. Basically it's max-dotclock delivery of the refresh cycle, followed by a longer VBI. Meaning, for a 120Hz QFD mode (via Large VT) in a 1/120sec (8.3ms) refresh cycle (assuming VT2600 with Front Porch padding), the refresh cycle shows up in the first 3ms, instead of taking the full 8.3ms to scanout. This can reduce VSYNC ON and VRR latency a bit (there is no effect on VSYNC OFF lag due to its scanout-following nature).

Try Appendix A pf http://www.blurbusters.com/crosstalk on both the 600MHz and the 640MHz dotclocks -- but try the 640MHz first.
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k2viper
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by k2viper » 30 Jan 2018, 15:36

Chief Blur Buster wrote:VT1302 at 240Hz works? That's the first time I've seen Large VT's be used at 240Hz.

Maybe LG intentionally used Large Vertical Totals in their EDID. That's a first!

Large VT in EDID?
Did you configure 640MHz, or was this automatically done by the monitor? That means it was embedded in its EDID (the plug and play feature where monitor tells the computer what video signal timings it supports). What does ToastyX say for LG's default 144Hz and 120Hz? I'd love to know if they embedded Large Vertical Totals in EDID -- that would be a QFD trick (Quick Frame Delivery) that can reduce the input lag of FreeSync further as well as VSYNC OFF. Could you screenshot the ToastyX screens for 144Hz and 120Hz EDID?
All I did when creating custom res (via Nvidia panel) - raised VT for 1302. 1310 isnt working already, since @ default it results in >640 pixeclock.

ToastyX for 144 and 240 default (not my currently running custom with VT 1302)
Image Image
Chief Blur Buster wrote:Large VT at max Hz means overclocking headroom
Have you tried overclocking? Large VT capability at max Hz means overclocking headroom, too!
This suggests potentially a (1300/1080)x overclocking factor available -- over 280Hz refresh rate at Reduced Blanking. Have you tried 250Hz?
Not yet, since I'm really interested only in modes which I can use strobing. I'll try it later when I'll have time.
Just played some Overwatch matches and monitor is awesome, had my s76 accuracy even at 52-55% intead of usual 45%, but I'm not sure that was fully courtesy of new screen :)
EXTRA STEP: If monitor does not have an adjustable strobe phase / area setting, try this additional step:
NOTE: This only applies to other brands than BenQ/Zowie (has a manually adjustable phase) and other brands of strobe backlights than ULMB/LightBoost (has a fixed pre-adjusted strobe phase)
Try keeping Vertical Total the same, but swap the Back Porch and Front Porch numbers. Test a motion test again, to see if the strobe crosstalk zone has shifted upwards/downwards (closer to being pushed off the top/bottom edge of screen). Try using a small “Sync” number, but use a larger value in either the Vertical “Front Porch” or Vertical “Back Porch”.
This step seems not working, I dont see any difference in crosstalk when swapping back and front porch numbers.
Maybe I'll experiment with it later, or other users buy this monitor, since it looks attractive at its price and performance.

ps. Its advertised with "low input lag" mode (dynamic sync), but there's no such item in OSD.

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by Falkentyne » 30 Jan 2018, 15:58

Can you do me a favor?
Can you check to see if it does blur reduction at 60hz, and if it SINGLE Strobes or DOUBLE strobes?
single strobe is obvious--there will be massive flicker but smooth image.
double strobe=double image, no flicker.

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by Chief Blur Buster » 30 Jan 2018, 16:25

k2viper wrote:This step seems not working, I dont see any difference in crosstalk when swapping back and front porch numbers. Maybe I'll experiment with it later, or other users buy this monitor, since it looks attractive at its price and performance.
Did you test this at 120Hz? You need very huge shifts (e.g. easier to see if moving 1000 between the two, not just 100 or 200) for noticeable vertical crosstalk-band shifts. So you want to try the ~VT2600 trick at 120Hz, then if it works, shift more than 1000 between Front Porch and Back Porch, to see if there's a significant crosstalk shift upwards/downwards. It's very monitor-dependant, depending on where in the refresh cycle, they trigger the strobe backlight.

The bigger the VT, the fainter the double-image strobe crosstalk effect should be, if the LCD is doing synchronous-scanout. Do you see any change between VT1180 versus ~VT2600 for 120Hz?
k2viper wrote:ps. Its advertised with "low input lag" mode (dynamic sync), but there's no such item in OSD.
It's possible it is always enabled. Or the menu item disappears in either strobed mode or VRR mode.
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k2viper
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by k2viper » 31 Jan 2018, 01:56

Falkentyne wrote:Can you do me a favor?
Can you check to see if it does blur reduction at 60hz, and if it SINGLE Strobes or DOUBLE strobes?
single strobe is obvious--there will be massive flicker but smooth image.
double strobe=double image, no flicker.
In 60Hz mode, 1ms blur reduction (strobing) feature in OSD is just greyed out. MBR is working for 120, 144 and 240hz.

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k2viper
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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by k2viper » 31 Jan 2018, 02:00

Chief Blur Buster wrote: The bigger the VT, the fainter the double-image strobe crosstalk effect should be, if the LCD is doing synchronous-scanout. Do you see any change between VT1180 versus ~VT2600 for 120Hz?
Havent tried tweaks for 120hz yet, maybe in next days.
Chief Blur Buster wrote:It's possible it is always enabled. Or the menu item disappears in either strobed mode or VRR mode.
VRR mode always off (since i have Nvidia card), but toggling off strobing doesnt show Dynamic action sync item. Well, lets count it always enabled.

BTW, monitor supports (and has in package contents) HDMI, is it possible that HDMI connection could be any better then Displayport? I connected DP as it was recommended in user manual. My 1070 nvidia has both DP and HDMI outputs.

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by Falkentyne » 31 Jan 2018, 03:32

Thank you.
What is up with all these monitor manufacturers that refuse to enable 60hz strobing these days?
Especially with all these 60hz console ports....seriously...

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by k2viper » 31 Jan 2018, 03:42

Benq strobe utility shouldnt work on this LG? Never used it before.

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by k2viper » 31 Jan 2018, 11:20

Tried 250 and 260hz with standard VT. Modes work, showed desktop, but display continuously show "Out of range" error message. So modes are unusable :)

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Re: LG 27GK750F-B - 240Hz, 27" 1ms Blur reduction

Post by Chief Blur Buster » 31 Jan 2018, 11:40

k2viper wrote:Tried 250 and 260hz with standard VT. Modes work, showed desktop, but display continuously show "Out of range" error message. So modes are unusable :)
260Hz works? Neat. Mind if you briefly try 280Hz with Reduced Blanking?

But, boo, gotta dislike "Out of Range" errors for successfully working overclocks.
Wonder if the Factory menu has a method of disabling these "Out of Range" errors.
Or if they can be dismissed by a menu button.

I wonder what the highest true Hz the LG can achieve for reduced porches (or even reduced resolution).
And I wonder if they work without frame skipping!

280/240 = 1.16 = 16% difference. My math calculations indicate 280 Hz would reduce lag randomization (MIN/MAX) by ~15% compared to 240Hz. (16% of 1/240sec = 0.6ms reduction of lag variability during VSYNC OFF). And also reduce maximum VRR input lag and VSYNC ON input lag by an average of 0.3ms (screen center is half refresh cycle) with 0.6ms lag reduction for screen bottom. And assuming GtG wasn't limiting factor yet, reduce sample-hold motion blur of full framerate material by up to ~15%.

Tiny numbers to be sure, but slightly bigger percentage difference than IPS 144Hz versus IPS 165Hz, as motion blur is sometimes more noticed by percentage differences than by the absolute Hz number. I wonder if other 240Hz monitors are equally overclockable.
k2viper wrote:Benq strobe utility shouldnt work on this LG? Never used it before.
No, it is not supported. But some of the tricks can be partially achievable in other (harder) ways -- strobe crosstalk shifting via Porch tricks.,
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

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