Optimal VT tweak for BenQ XL2420Z?

Ask about motion blur reduction in gaming monitors. Includes ULMB (Ultra Low Motion Blur), NVIDIA LightBoost, ASUS ELMB, BenQ/Zowie DyAc, Turbo240, ToastyX Strobelight, etc.
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SUOrange55
Posts: 30
Joined: 16 May 2014, 10:31

Optimal VT tweak for BenQ XL2420Z?

Post by SUOrange55 » 10 Sep 2015, 14:03

Hi,

I'm a bit confused by which VT tweak to use. Will VT 1502 @ 125hz (with the pixel patcher) eliminate almost all of the crosstalk at the 100+ refresh rates? Thanks.

Falkentyne
Posts: 2793
Joined: 26 Mar 2014, 07:23

Re: Optimal VT tweak for BenQ XL2420Z?

Post by Falkentyne » 10 Sep 2015, 15:56

Just a few things: (and this really should be in the Benq section; this section is for Lightboost and ULMB (ULMB is the sequel to Lightboost, for Gsync monitors)

1) The higher the refresh rate, the more crosstalk you will have on the screen. That's simply because there's less time for pixels to complete transitions, which after all makes sense; 60hz has a 16.7 millisecond response time and 144 hz has a 6.9ms response time. The average vertical blanking period (Chief please correct me if I'm wrong) is around 0.5 millisecionds; a VT tweak helps increase this to around 2 ms, although I'm probably incorrect with the numbers. Obviously the vertical blanking period only matters when backlight strobing is in use; it's irrelevant for normal sample and hold, since there's no strobing and thus no crosstalk.

I think you can easily see that there will be DOUBLE the amount of crosstalk at 120 hz refresh rate (8.3ms) than at 60 hz (16.7 ms). (if you enable "Single Strobe" in the service menu and test 60hz and 120hz (without a VT tweak) then you will see that for yourself.

2) while 60hz goes out of range at even VT 1350, 61hz works with VT 1502. If you tested this with a custom resolution, you would notice there is absolutely NO strobe crosstalk on the screen anywhere (if the strobe duty is low enough). Increasing the strobe duty will bring the top areas strobe pulse crosstalk downwards (this also will move the bottom downwards as well, no one knows why this behavior exists, however).

3) The maximum VT the Benq monitor will accept is 1502. This is a scaler limitation and it seems to be firmware related. This may not be unique to the Z series; it seems like the non blur reduction T series (that had lightboost only) reacted the same way. What seems to be happening is that the SCALER's resolution that it processes seems to be based on the vertical total value, instead of the physical screen resolution data. So the entire reason our vertical total tweaks work seem to be an untended "bug" rather than a feature. Of course you can call them a "feature" too.

Let's take a custom resolution.
But do you have Version 4 firmware? You will need V4 firmware in order to test this.

Assuming you do, unlock the factory menu:
1) power off the monitor, then hold Enter+Menu (button 3 and 4) for 5 seconds.
2) Press power on (don't hold down power though) while holding the two buttons then release the buttons.
The eye care and input prompt will be bypassed, the OSD timeout will be set to 'Infinite' and button #5 enters the factory menu.

The factory menu will show the SCALER resolution. This MAY be different than the OSD "information." The OSD information tab reports the physical resolution signal sent by the video card (E.g. 1920x1080 will always be reported as 1920x1080, and custom display scaled resolutions (e.g. 1024x768) will be reported as 1024x768. The OSD will report the "backlight strobe pulse widths" as the refresh rate instead of the real refresh rate, so ANY resolution with a vertical total tweak will report 60hz (60hz pulse widths are being used for the strobed backlight).

First let's do something interesting.
Make a 120hz custom resolution without a VT Tweak.
We will use the default settings that 120hz usually takes for automatic timings.

If you already have a toastyX config, you can just "export" it and then import it again later when we're all done.
Let's remove the old vt tweak and get with the defaults.

In ToastyX CRU, enter these values:
Active : 1920, 1080
Front: 48, 3
Sync: 32, 5
Back porch: automatic fill in
sync width: automatic fill in
Horizontal Total : 2080
Vertical Total : 1144
Refresh : 120hz
Horizontal khz: automatic fill In
Pixel clock: automatic fill in

Save exit and restart the driver (restart64.exe)
Enter the factory menu.

Notice the scaler resolution is reported as 1920x1080@120hz. Ok no problems.

Now watch this.
Change the Vertical total from 1144 to 1125.

Save and restart the driver.
enter the factory menu.

See what just happened?
The scaler is reporting : 1400x1050 @ 120hz !
Now go to the OSD System->Information. That shows 1920x1080@120hz.
The scaler does NOT.

Apparently, the vertical total influences the scaler resolution.
The scaler is what controls the aspect settings and screen sizes of the display mode settings, although the actual physical size of the screen "emulated" positions (like 17", etc) seem to be fixed.

The scaler is also what handles the strobe crosstalk calculations. The crosstalk position on the physical screen depends on what vertical size the scaler is working with. The horizontal does not seem to be important. No one knows why the horizontal DECREASES this much with just 29 decrease in VT! The vertical seems right on point... 29 decrease in VT = 30 point decrease in scaler vertical resolution.

So now let's go back and see what's going on with our magical scaler!
Delete the resolution you made or just import the old VT 1502 one back in and restart the driver.

Go to 120hz VT 1502.
Enter factory menu.

.............what is this?!?!
The scaler is reporting 1280x1440 !!!!

Yes........the scaler thinks it's working with a 1440 vertical resolution !!
And the math actually adds up completely.

Default VT at 120hz is 1144.
Our custom VT is 1502.
This is a 25% increase in VT.
The panel is a 1080p panel (1920x1080).
The scaler reports 1280x1440.
sure enough this is a 25% increase in vertical resolution!

But we have a PHYSICAL panel size of 1080 lines (horizontal lines, counted vertically (height). (1920 width, 1080 height).

This is starting to make sense isn't it?

The scaler is working with a panel size of 1440 pixels in its memory space. The crosstalk in blur reduction is based on the scaler resolution. Therefore, on the actual physical panel, the crosstalk is actually pushed downwards off screen! The top crosstalk remains at the same position as before, which is pretty obvious here--the panel starts scanning at the same spot, regardless of the resolution (the scanning spot can be changed by increasing the "Strobe phase", although increasing the strobe duty also affects this.

So this is why our vertical total tweaks work.

The VT limit of 1502 is either a scaler limitation or a resolution limitation in the firmware. There are references in the raw firmware dump to 1440p resolutions even though the monitor is not "capable" of that natively. There is a 2560x1440 resolution listed (16:9) and a 2560x1600 resolution listed (16:10).

Now knowing how our vertical total tweaks affect the scaler allow us to do some other crazy stuff.

Enter these timings on your monitor (ITS BEST if you are using Displayport; DVI is YMMV but make sure you have the pixel clock patcher).

Active:
horizontal: 2560
Vertical: 1440

front porch 48, 3
Sync width 32, 5
Horizontal total: 2656
Vertical total: 1500
Refresh rate: 100 hz.
Pixel clock (398.40 MHz)

Save and restart the driver.
Select 2560x1440@100hz in the video card control panel.

What happens?

What does the SCALER resolution report as?
What does the OSD information report?
How is the crosstalk in comparison to 1920x1080@120hz VT 1500?

(Note: 2560x1600 is impossible. The scaler will not accept a VT higher than 1502, but the lowest possible VT for 2560x1600 is 1609....)

SUOrange55
Posts: 30
Joined: 16 May 2014, 10:31

Re: Optimal VT tweak for BenQ XL2420Z?

Post by SUOrange55 » 10 Sep 2015, 16:22

Thank you for the reply.

I'm using V2 firmware at the moment and the Nvidia Driver Panel - do I need to do anything other than setting the refresh rate / VT in Nvidia?

Falkentyne
Posts: 2793
Joined: 26 Mar 2014, 07:23

Re: Optimal VT tweak for BenQ XL2420Z?

Post by Falkentyne » 10 Sep 2015, 17:28

I have an AMD card so I don't know how the Nvidia control panel works.
If the OSD reports 1920x1080 @ 60hz refresh rate with your VT tweak (at 100hz or 120hz, it should still report 60hz) then the VT Tweak worked. If it reports 100 or 120hz, then it didn't work.

If you do upgrade to V4 firmware, my long post will make a lot more sense.
BTW you can still try the stuff I posted. It works on V2 also; you just don't have the factory menu to report the scaler resolution.
Also keep single strobe ENABLED on V2 firmware. Having it disabled causes a few issues when switching resolutions or modes (this was fixed on V4).

SUOrange55
Posts: 30
Joined: 16 May 2014, 10:31

Re: Optimal VT tweak for BenQ XL2420Z?

Post by SUOrange55 » 12 Sep 2015, 08:00

Having some issues after trying to apply the VT tweaks -- my desktop/Windows image is all screwed up (full screen games look fine). Tried re-installing my drivers / resetting monitor to no luck. Anyone ever have this happen?

Image

Falkentyne
Posts: 2793
Joined: 26 Mar 2014, 07:23

Re: Optimal VT tweak for BenQ XL2420Z?

Post by Falkentyne » 12 Sep 2015, 09:42

What exactly is the problem?
the white and blue color? The black line going through the image like something drawn in paint? or something else?

SUOrange55
Posts: 30
Joined: 16 May 2014, 10:31

Re: Optimal VT tweak for BenQ XL2420Z?

Post by SUOrange55 » 12 Sep 2015, 10:02

The colors are all screwed up. For example, some of my desktop icons have random black backgrounds and everything looks very pixelated and washed out.

Falkentyne
Posts: 2793
Joined: 26 Mar 2014, 07:23

Re: Optimal VT tweak for BenQ XL2420Z?

Post by Falkentyne » 12 Sep 2015, 11:16

Really not sure what's going on.
The only artifact with a VT tweak is a horizontal faint scanlines effect; this is also seen in an almost identical fashion in Lightboost mode, because a VT tweak (effectively) does the same thing as Lightboost does via the LC panel timing: accelerating the scanout so that the pixels can complete transitions within the strobe blanking period.

Are you using an Nvidia card? (Strobelight will not work on this monitor to unlock Lightboost). If so you can try the INF override+CRU trick + 3d vision drivers to enable Lightboost mode. If you can do that, look to see if you get the same issue on the screen.

But before that, what timings are you using for your vertical total tweak? You may be using too tight timings.

The correct timings for both 100hz and 120hz should be:

Horizontal/Vertical active:
1920 / 1080

Front Porch: 48,3
Sync width: 32,5
Horizontal Total: 2080
Vertical total: 1500-1502.

At 100hz, Pixel clock should be 330.00 MHz with 1500 VT and 330.44 MHz with 1502 VT.
At 120hz, the pixel clock should be 374.40 with VT 1500.

(Note: the default Vertical total for 100hz is 1133 and the default vertical total for 120hz is 1144)

SUOrange55
Posts: 30
Joined: 16 May 2014, 10:31

Re: Optimal VT tweak for BenQ XL2420Z?

Post by SUOrange55 » 12 Sep 2015, 14:02

I'm not using any VT tweaks at the moment. What happened was that I set VT 1502 in NVCP and then tried to enable Blue Reduction via the OSD, screen went black every time that the monitor went into BR mode. Then my desktop went mad. It looks like 16 bit colors or something.

Falkentyne
Posts: 2793
Joined: 26 Mar 2014, 07:23

Re: Optimal VT tweak for BenQ XL2420Z?

Post by Falkentyne » 12 Sep 2015, 16:41

The default strobe phase for blur reduction is 100.
This is set this way after a full hardware or factory reset. I "think" the Internet café setting in the service menu also causes a factory reset when the power button is turned off.
Using a VT Tweak limits the maximum strobe phase allowed, because the persistence values are changed and (far more complicated), the vertical resolution that the scaler works with for the strobe phase is "increased" past the physical panel size. With a VT 1500 tweak, the maximum strobe phase is 059 at 120hz and 050 at 100hz. Going past this will turn off the backlight if MBR is enabled.

You need to go into the service menu and set the strobe phase to 000. Then enable blur reduction.
There really should be a sticky for these commands.

Power off, hold button #4 for five seconds, press power on while holding down button #4, then release.
This unlocks the service menu.

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