Vega wrote:The question would be is BenQ really going to release a native 240 Hz strobing monitor with massive cross-talk? Or how are they running it above the magic 182 Hz number?
First, let me simplify things --
The good news is that XL2540 and XL2546 has an adjustable strobe timing/phase support, and supports large Vertical Totals via Custom Resolution Utility. The XL2540 already has strobing support (like XL2546) but it's hidden in a Service Menu. The original XL2540 also strobes at all refresh rates, including 240Hz.
1. There's almost no strobe crosstalk at lower refresh rates
(120Hz and less) when using large Vertical Totals (via ToastyX)
2. Single strobing is supported at all refresh rates in sub-1Hz-increments
3. It's an analog continum
of gradually worsening strobe crosstalk, the higher the refresh rate you go.
4. Therefore, it's a user choice. You use the highest refresh rate that you can tolerate the strobe crosstalk on.
De-facto, the Blur Busters Community has declared 182Hz as a compromise for good strobing on the XL2540 -- after proper calibration of Strobe Phase ("Area"), the strobe crosstalk is roughly similar to current ULMB monitors running at their maximum refresh rates. For some refresh rates, the bottommost 1/10th sliver of screen and topmost 1/10th sliver of screen may be worse than ULMB -- while center of screen has almost zero strobe crosstalk (i.e. sometimes better than ULMB). It really depends on refresh rate and Vertical Total tweaking. Some people will prefer lower (even less strobe crosstalk), and some people will prefer higher (more strobe crosstalk).
Example: You tested a "X" Hertz and it looks good. You think you can tolerate maybe 2% more strobe crosstalk? Try bumping Hz upwards by say "X + 1Hz" or "X + 5Hz". Then you keep trying until the strobe crosstalk begins to look slightly too visible. Then you back off a bit. And stick to your preferred Hz. Above ~180-200Hz(ish) the crosstalk will rapidly get worse and fiddlier as your ability to use Vertical Totals slowly diminish (VT becomes smaller and smaller till it's a reduced blanking interval) -- you're forced to use reduced totals at the maximum refresh rate (i.e. display cannot scan-out faster than 1/240sec at 240Hz). You're pretty much increasing scanout speed as much as possible via the huge Vertical Total trick -- basically configuring your scanout to scan 1/240sec, no matter what refresh rate you're targetting. The higher your refresh rate, the less time between the 1/240sec scanouts, which is incrementally less-and-less room for the ~1ms LCD GtG (to mostly complete) -- and we know "1ms GtG" hype isn't really "1ms-perfect-complete" for all color combos. You're see increasing intensity of strobe crosstalk a percent (or few) for every 1Hz step upwards that you test....as you test 190Hz,191Hz,192Hz,193Hz....in the ever-marching testing towards 240Hz. There's a sweet spot compormise, and the Community here decided (give or take) that best compromise is occuring at (approximately) 180Hz(ish) for what looks roughly ULMB-quality strobing.
The larger the Vertical Total, the more the strobe crosstalk disappears. (For example, every 0.1ms added to Vertical Total can fade the strobe crosstalk by another 10%). Until you bang hard against the dotclock limit of your monitor. >VT2000+ is supported at 120Hz (which means it scans out a 120Hz refresh cycle in approximately 1/240sec -- creating a healthy 4ms pause between refresh cycles to let 1ms GtG finish), and >VT1500+ is supported at 182Hz, which are excellent. If you don't mind say, 10% more strobe crosstalk, you can go to 190Hz or 195Hz, for example -- and so fourth. It's a continuum of strobe crosstalk intensity, as XL2540 supports refresh rate in roughly sub-1Hz increments. You simply choose a refresh rate and then maximize the Vertical Total, and adjust the strobe timing (via "Area" setting in Service Menu) so that the flash is earlier/later -- minimizing the double-image effect at either top or bottom edge. If you adjust strobe timing (Area setting) while watching a full-screen TestUFO.com/photo -- you'll notice the horizontal "strobe crosstalk zone" (LCD GtG zone) move upwards and downwards. And the smaller the Vertical Total, the more the horizontal "strobe crosstalk zone" (LCD GtG zone) disappears off the bottom edge of the screen before wrapping-around to the top edge of the screen.
The higher the refresh rate, the taller the height of the strobe crosstalk zone becomes. So it's great user choice that BENQ let the user be able to choose how much strobe crosstalk they can tolerate -- the more the user tolerates it, the higher the refresh rate. There's almost near-zero strobe crosstalk at 1080p@120Hz (better than LightBoost) when strobe timing is properly manually adjusted in Service Menu (remember: BENQ is one of the few manufacturers with a user-adjustable strobe flash timing adjustment in Service Menu), and the strobe crosstalk gradually worsens the more you increase refresh (in 1Hz steps) towards the maximum. At 240Hz, you're stuck with Reduced Blanking (That means Vertical Totals that are barely bigger than vertical resolution -- this is bad for strobe crosstalk), but the more you lower the refresh rate, the bigger your Vertical Total becomes, the less strobe crosstalk occurs, in an analog continuum of user choice. That's the great thing...
Yes, it's kinda complex to adjust, but at least the user choice is there.
BENQ XL2720Z users have been doing this for years now, with Strobe Phase ("Area") / Strobe Length support. Fortunately, adjustments still remain in the XL2540 for optimizations. Obviously, you will get lots of strobe crosstalk out-of-box, and you have to use ToastyX and Large Vertical Totals to make strobe crosstalk magically disappear.
The XL2546 makes it much easier to enable and access strobing. It might even support even larger Vertical Totals than XL2540 (untested), which may reduce strobe crosstalk on XL2546 over XL2540.
If you don't have an hour to adjust strobe phase, don't bother getting the "DIY Vertical Total" method of reducing strobe crosstalk -- it has a learning curve involved in order to manually adjust to make things look as good as ULMB at the highest refresh rate possible (~160-200Hz(ish) depending on user threshold of tolerance for strobe crosstalk). NVIDIA ULMB makes it easy by automatically doing everything for you, but you're limited to certain refresh rates.
The most problematic monitors were the Version 1 of the XL2720Z which had an unadjustable strobe timing that created an ugly fixed (non-adjustable) strobe crosstalk zone (LCD GtG zone). A stationary double-image zone
as a horizontal band that stayed stationary about 2/3rds down from the top edge of the screen.
That's what happens if you flash a strobe backlight (Blur Reduction) while the LCD GtG Zone is still on the screen. Not good for an image-quality aim, although it might slightly reduce lag at the crosshairs (This might have been what BENQ was originally tying to do, as input lag is lower just above the crosstalk zone, than below the crosstalk zone -- I'm imagining BENQ probably put a lag sensor in the middle of the screen, and adjusted strobe timing until minimum lag -- creating this visually-flawed XL2720Z setting).
Many users complained, and BENQ released a firmware update
(Version 2) letting the user adjust strobe flash timing so that this artifact can be fixed. Adjusting while watching a TestUFO test, causes the crosstalk-zone (LCD GtG Zone) to move upwards/downwards, as the flash timing is changed. You adjust until you push this zone off the bottom edge of the screen. Unfortunately, when Vertical Totals get tight, the crosstalk will reappear at top edge long before most of the crosstalk is pushed below bottom edge of screen. Now, the bigger you can make Vertical Total, the more you can push the crosstalk zone off the bottom edge of the screen without affecting the top edge of the screen.
(ULMB, while it does things far more automatically out-of-box -- has the same top-and-bottom-edge crosstalk problem too, and NVIDIA makes compromises by choosing specific fixed settings, usually in combination with a Y-axis-compensated LCD overdrive table that uses more aggressive overdrive at the bottom edge of the screen... That's a topic for another day)
At this time, BENQ has kept strobe timing adjustable on all XL Z-Series (Version 2 and later) and their Zowie variants, on XL2420G, on XL2735, on XL2540 (complex adjustments via Service Menu), and XL2546. It's possible to manually tweak timing/phase until it looks as good as ULMB (and better, if using a lower refresh rate and massive vertical totals!). It's a lot more work, but very rewarding when you're rewarded with a better-than-ULMB after 1 hour of manual tweaking.
Since then, BENQ now lets users adjust most of their newer 144Hz-240Hz monitors to preference -- priority to lag versus priority to minimizing strobe crosstalk. Not all users realize that they can fix strobe crosstalk on their BENQ monitors via the service menu, and via Large Vertical Totals in CRU. Some users have bought a BENQ, saw terrible strobe crosstalk, and returned the monitor -- without realizing that spending an hour adjusting this can make it look practically as good as ULMB (As long as you "back off" the refresh rate by approximately 25%-ish).
The only BENQ strobed monitors (post-LightBoost) with unadjustable strobe crosstalk XL2720Z (Version 1) and XL2730Z (all versions). All the other BENQ/Zowie can all successfully strobe in 1Hz increments. Including all 240Hz BENQ monitors, have strobing that becomes very good when combining BOTH (A) proper Vertical Total adjustments and (B) Adjusting "Area" setting, and (C) Choosing a refresh rate where strobe crosstalk doesn't bother you.
Anyway... XL2540/XL2546 has totally adjustable strobe crosstalk, which is a Great Thing. They actually let you CHOOSE which refresh rate you begin to hate strobe crosstalk at. (Usually that's >180Hz for most people, at least on the earlier XL2540).
Understand better?...Yep, Blur Busters will probably need to create an easy "How To Reduce Strobe Crosstalk on BENQ Monitors" instruction page. There's already sort of instructions at http://www.blurbusters.com/strobe-utility -- but it doesn't work on XL2540s, but the same TestUFO "Alien Invasion" test can be used while adjusting the BENQ Service Menu "Area" setting -- while experimenting with new large Vertical Total modes in ToastyX CRU. (To speed things up, there's already a 182Hz ToastyX CRU screenshot in one of these threads)