BenQ XL2420Z

Responsiveness

Input lag

We used SMTT 2.0 and a sensitive camera to compare the XL2420Z’s latency with a range of other monitors of known latencies. ‘Instant mode’ was on throughout this and indeed all of our other testing. This minimises image post-processing to reduce latency, with no noticeable impact on image quality. We compared results at 100Hz and 144Hz, with and without the ‘Blur Reduction’ (BR) mode activated. At each combination of refresh rate and BR mode 30 photographs were taken and an average input lag worked out. We recorded 1.5ms of input lag at 144Hz without any measurable difference with BR mode activated. This rose slightly to 2.5ms at 100Hz, again with no measurable effect when activating BR mode. The monitor therefore produced good and consistently low input lag in all of the operating modes tested which is good to see.

Pixel responsiveness

We used a tool called PixPerAn (Pixel Persistence Analyser) and a sensitive camera to assess the pixel response performance of the monitor. PixPerAn was set to the highest movement speed (tempo) with the monitor set to various refresh rates. Each refresh rate was tested at each of the 3 AMA (Advanced Motion Acceleration) settings. The images below are photographs captured with AMA ‘Off’ at 60Hz, 100Hz, 120Hz and 144Hz, respectively.

60Hz AMA 'Off'

100Hz AMA 'Off'

120Hz AMA 'Off'

144Hz AMA 'Off'

At 60Hz you can see a fairly bold primary trail and a faint secondary trail with AMA set to ‘Off’. At 100Hz both trails become weaker, with similar results seen at 120Hz and 144Hz as well. The images below show the results with AMA set to ‘High’ at 60Hz, 100Hz, 120Hz and 144Hz, respectively.

60Hz AMA 'High'

100Hz AMA 'High'

120Hz AMA 'High'

144Hz AMA 'High'

At all refresh rates, with AMA set to ‘High’, the conventional trailing has been replaced by brighter and darker trails – a phenomenon referred to as ‘inverse ghosting’ or ‘overshoot’. In the images this appears perhaps strongest at 60Hz and weakest at 144Hz but is common to all. It is quite difficult to directly compare these particular photos to those taken on the XL2411T (which is itself similar to the new 144Hz XL2420T and 20TE) because a different camera was used. It would seem that very little has changed with the ‘AMA High’ setting compared to other XL series models and the intensity of inverse ghosting in this test is very much the same. It’s not something that many users actually notice and even fewer are bothered by it, but there is no denying that it’s there. The images below show the results with AMA set to ‘Premium’ at the usual respective refresh rates.

60Hz AMA 'Premium'

100Hz AMA 'Premium'

120Hz AMA 'Premium'

144Hz AMA 'Premium'

You can see that the inverse ghosting has intensified. It becomes a lot more noticeable and widespread in practice whilst you gain no reduction in motion blur at all using this setting. We’d personally like to see BenQ use their current ‘AMA High’ setting as ‘AMA Premium’ and slightly lower the acceleration of ‘AMA High’ to provide a useful setting to users who are particularly sensitive to inverse ghosting. Wishful thinking aside, we used ‘AMA High’ for our testing because it provided the best performance out of the 3 settings.

But what about refresh rate? Why did this not seem to have much effect in the trailing captured on these images? PixPerAn involves taking static photographs to capture pixel transitions at that given snapshot in time. What they don’t take into account is the pixel transitions occurring over time, for example in one second. When you set the monitor to a higher refresh rate it actually gives you more visual information every second. At 120Hz, for example, it’s giving the user twice as much visual feedback every second as at 60Hz. At 144Hz it’s giving the user even more. The car used in the PixPerAn test actually crosses the screen twice as quickly at 120Hz as at 60Hz (and at appropriate speeds proportional to the other refresh rates) at the same tempo setting.

When you’re playing a game at 120Hz you obviously don’t expect everything to move twice as quickly (that would be a bit strange and cheat-like if nothing else). However; the monitor can still update the visual information on the screen twice as often. And that is exactly what it does. We explore the impact that this has in quite some detail in our dedicated responsiveness article, which is well worth a read when you have the time. There are a couple of important take-home messages about the effect of an increased refresh rate which are mentioned in detail in the article.

1) The majority of motion blur on a modern monitor is caused by eye movement rather than pixel response times. Provided frame rate also increases; an increased refresh rate decreases eye movement by giving the eyes more visual information to work with, hence reducing motion blur.

2) When a monitor provides more visual information to the user every second (i.e. by supporting and outputting increased frame rate action) the user feels more ‘connected’ to the game. The monitor responds more frequently to user inputs, including mouse movements. This gives a certain feeling that no 60Hz LCD can replicate regardless of how low its signal delay is.

In the following section we subjectively assess the responsiveness of the monitor at 144Hz in a range of game of movie titles. We see how everything fits together in practice and shapes the responsiveness of the monitor in the ‘real world’.

Responsiveness in games and movies

At high frame rates 144Hz provided an excellent connected feeling on Battlefield 4. The interaction with the game world had a glassy smoothness to it that you simply don’t get on a 60Hz monitor. The level of motion blur was very low without any observable trailing from the pixel responses being too slow. There was a degree of motion blur caused by eye movement – an important concept explored previously – but this was significantly reduced compared to even the fastest 60Hz displays. This made spotting enemies whilst moving quickly a lot easier. There were some hints of overdrive artifacts in places but these were faint, short-lived and difficult to notice when actually playing the game. At lower frame rates the advantages in motion blur reduction vanish and although the monitor still has very low latency (and the ‘input lag penalty’ to using VSync is reduced) you don’t get the same level of connectedness. So overall the monitor provided the snappy pixel responsiveness and extremely low latency to put the 144Hz refresh rate to good use, provided you can pump out well over 60fps to really benefit from it.

The 144Hz refresh rate doesn’t really have the same impact on racing games such as Dirt 3 as it does on First Person Shooters. It does greatly reduce motion blur, though, meaning the world remains sharper as you race past it. This is particularly nice during Gymkhana as it makes the experience less dizzying. For hardcore racers it’s also nice to have the image on the screen update itself in response to your input more often. There were again some instances of fairly faint and short-lived inverse ghosting. Nothing that we noticed passively and not something that will spoil the experience for most users.

Because movies run at a fixed frame rate of around 24 fps, and you don’t interact with them, the 144Hz refresh rate doesn’t have the same impact as it does on games. Unlike on a 60Hz monitor, though, the 24fps of movies divides evenly into 144Hz – each frame is displayed 6 times. This removes most of the ‘juddering’ that can be observed on a 60Hz monitor. The same effect can be observed by setting the monitor to 120Hz or setting a ‘custom resolution’ using multiples of 24. There is still no mistaking that the content is running at around 24 fps, though, and the overall fluidity of the motion simply doesn’t compare to high frame rate game content.

Blur Reduction

What is it?

Referred to as ‘Motion Blur Reduction’ on BenQ’s online material and simply ‘Blur Reduction’ on the monitor itself, this is a strobe backlight mode designed to reduce perceived motion blur on the monitor. We have explored the notion of ‘strobe backlights’ in our responsiveness article – which is well worth a read if you want a deeper understanding of the science behind this technology. On a basic level the backlight of the XL2420Z pulses (strobes) ‘on’ and ‘off’ at a frequency corresponding to the refresh rate of the display. A greater amount of time is spent ‘off’ than ‘on’; much like an old CRT monitor. This limits the amount of time that your eyes spend smoothly tracking motion on the screen, something which an increased refresh rate alone will do to some extent but not to the same degree as a strobe backlight. As we mentioned earlier, this is important because the movement of your own eyes is actually the most significant contributing factor to perceived motion blur on a modern monitor.

A note about strobe crosstalk

Before talking about our own personal experiences with the ‘Blur Reduction’ feature, we’d like to take a little bit of time to address an issue that has quite unnecessarily put a lot of users off the this monitor. This relates to so-called ‘strobe crosstalk’ whereby certain areas of the image suffer from a ghosting effect due to the strobe behaviour of the backlight. The same effect can be observed on other strobe backlight implementations such as ‘Nvidia LightBoost’. This issue can be illustrated very nicely using the Alien Invasion UFO Test. The photograph below was taken on the BenQ running its ‘Blur Reduction’ mode at 120Hz. Google’s Chrome browser was used with the test running full screen. This issue is not specific to only the 120Hz refresh rate, but this specific test is designed to work well at 120Hz.

In this image you can see a bold black band which is most noticeable a little way below the centre of the screen but not-existent towards the top of the screen. We also captured this behaviour in Battlefield 4. The snapshots below show how things look to the camera when strafing past a dirt bike. In the top image the wheel of the bike is near the top of the screen, so you don’t have that bold crosstalk. In the bottom image the same bike is strafed past in the same way with the wheel towards the bottom of the screen at the region most affected by strobe crosstalk – quite a clear difference in this example. The monitor is set to 144Hz.

BenQ states that they are quite happy with how things are set up on their XL-Z series monitors regarding the ‘Motion Blur Reduction’ feature. They are not going to alter this behaviour but have provided firmware which will allow the strobe backlight behaviour to be modified by third party utilities. One such utility is the Blur Busters Strobe Utility. This allows you to adjust the ‘Persistence’, a slider which alters the length of the ‘on’ and ‘off’ phases. A longer ‘on’ phase creates a brighter image at the expense of increased levels of motion blur. You can also adjust the ‘Crosstalk’ by using the appropriate slider. This will alter where on the screen that aforementioned bold strobe crosstalk stripe appears but will never eliminate it completely.

Most units currently being sold feature the original firmware which can’t actually be adjusted using this sort of utility. It will likely take several months from when this review is published for updated firmware units to be sold by the usual retailers. If you are the kind of person who likes to tweak things yourself or do have an issue with how ‘Blur Reduction’ is implemented in the factory then you can send your unit to BenQ to have the firmware upgraded. You will have to cover the shipping costs but won’t have to worry about upgrading the firmware yourself – which can potentially go wrong. Some users will find ‘strobe crosstalk’ to be an issue, just like some don’t like the inverse ghosting. But many users should find things absolutely fine as they are and will really enjoy the benefits that the ‘blur reduction’ mode brings to games.

The experience at 144Hz

Although we’ve already explained why looking at what a camera sees in a static photograph is not a good reflection of what the human eye sees, it’s still interesting to look at the PixPerAn test once again with the ‘Blur Reduction’ mode activated. The photograph below was taken with this mode active at 144Hz and PixPerAn set up in the same way as before.

PixPerAn with Blur Reduction

During this transition the inverse ghosting appears fainter than it was without the strobe backlight mode activated. The inverse ghosting was certainly still there when gaming and not all transitions appeared to have this ‘muted’ in quite the same way as PixPerAn indicates. Even so, it’s nice to see it potentially dampened a bit with the strobe mode activated for users who are sensitive to this. It’s important to stress that most users will find that when they’re actually gaming rather than looking out for inverse ghosting it really ceases to be an issue. Many won’t notice it and very few will be at all bothered by it – especially given the overall fluidity of the experience.

Speaking of fluidity; using the ‘Blur Reduction’ feature at frame rates matching the refresh rate does nothing to upset the connected feel between man (or woman) and machine. In fact if anything it improves this further. The reduction in motion blur is something that many gamers will find quite dramatic. On Battlefield 4 you could clearly see the enemy at any pace of action. When turning rapidly the image ‘stabilised’ as good as instantly, giving the game a really sharp and snappy feel. After getting in a nimble vehicle things got really impressive. You could turn in an ATV (All-Terrain Vehicle) as quickly as you wanted without the environment turning into an enemy-masking blur. This level of sharpness also made spotting enemies particularly easy when quickly manoeuvring jets and helicopters – in fact it almost felt like cheating.

The seamless experience really did require a frame rate matching the refresh rate, however. As the frame rate dropped even slightly below this there was a sharp stuttering and definite disconnected feel to the whole thing. This same stuttering occurred with ‘Blur Reduction’ disabled, but it is masked by motion blur and simply isn’t as noticeable or dramatic in its effect on the visual fluidity. On Dirt 3 the strobe backlight mode also gave a superbly low level of motion blur. This was particularly noticeable on the Gymkhana mode, where the track and obstacles maintained surprisingly good clarity even during rapid spins.

The experience at 100Hz

Running this monitor in 100Hz during normal ‘sample and hold’ operation, with the strobe backlight disabled, generally leaves users wanting more in the way of responsiveness. It certainly feels like there is an awful lot of potential left unused. Without applying ICC profiles, though, 100Hz actually lifts the richness of the image a fair bit. You can’t pick out subtle variations in closely matched shades in the same way you would on an IPS (or PLS, or AHVA) monitor with their excellent shade consistency – it doesn’t magically enhance viewing angle performance in any way. But things do look relatively rich and full, which is important to many gamers.

If you then whack on the ‘Blur Reduction’ mode you maintain this richer appearance with pleasingly low levels of motion blur. When running the monitor in this mode there was noticeable sharp stuttering when the frame rate dropped below 100fps needed to match the 100Hz refresh rate. The 100fps target is of course easier to hit and maintain if you don’t have a supremely powerful system and don’t want to sacrifice eye candy. This was certainly the case with our single overclocked GTX 780, for example. But what is the experience like at 100Hz with blur reduction on? In short; surprisingly good. On Battlefield 4 there was a very good connected feeling. The monitor wasn’t updating itself as frequently as at 144Hz, but we felt that the overall feel was still very good. The level of motion blur was impressively low. Whilst technically not as low as running at 144Hz with the strobe backlight feature enabled, it was still extremely low. Significantly lower than running the monitor normally (sample and hold style) at 144Hz with a 144fps frame rate, in fact. Getting in an agile vehicle and turning rapidly still had that glassy smooth ‘wow’ factor – and strafing runs in aircraft still felt cheat-like.

Dirt 3 really reaped much of the benefits that were enjoyed when running the strobe mode at 144Hz. Even the rapid spins of gymkhana felt smooth and sharp rather than becoming dizzying and blurry. As a game that doesn’t get on with ICC profiles the extra colour richness was also welcome. Overall we found 100Hz with ‘Blur Reduction’ something of a sweet spot for gaming with this monitor on our system. It was the setting that impressed us the most, really.

A few quick points to end on. Running the strobe backlight mode at 120Hz is some way between the 100Hz and 144Hz strobe experience in terms of both non-profiled colour performance and responsiveness. And there is no benefit nor obvious responsiveness drawback to watching movies with ‘Blur Reduction’ enabled. As noted in the calibration section there is a degree of flickering due to the nature of the strobe backlight – and this is proportional to the refresh rate as the flickering is synchronised with this. Whilst it’s technically possible to run the monitor at 60Hz with the strobe function enabled (with games consoles connected, for example) it does create flickering that will be obvious and possibly uncomfortable for many users.

Conclusion

As with any monitor there are good points and there are bad points with the BenQ XL2420Z. On the outside this model is indistinguishable from the older XL2420T(E) and carries the same housing, ports and S-Switch accessory. There were no real surprises when it came to core performance, either. The out of the box image was truly an eyesore, with the ‘eye-care’ logo mocking the user in an ironic way as you turn the monitor on. It was possible to improve things so they were much more acceptable by tweaking various options in the OSD, but there was still a bit of a washed out and in places bleached look no matter what you did there. Interestingly colours became far richer and the image more appealing at progressively lower refresh rates. The monitor did respond well to calibration, though, making for a much more pleasant viewing experience once the ICC profiles were applied. It’s always a shame to have to rely on this level of correction rather than making simple OSD tweaks, especially since the average home user doesn’t own a colorimeter and our profiles won’t be optimal for every unit.

Contrast performance was also a bit mixed. Static contrast was actually very good and there was no peripheral loss of detail from ‘IPS glow’ or similar phenomenon on this TN panel. There was definite ‘gamma enhancement’ going on which revealed extra unintended detail in dark areas. This made some scenes look somewhat flooded but is designed to give a competitive edge when gaming. This actually reflects the native behaviour of the panel and is something we’ve seen on other monitors sharing the same panel, even without the ‘Black eQualizer’ feature. Once calibrated using an ICC profile this effect was actually reduced fairly significantly – and despite the clearly significant corrections made in the profiles, measured contrast didn’t suffer in a negative way at all.

Where this monitor really shone was its responsiveness. The input lag was exceptionally low and the pixel responsiveness very high, allowing it to make very good use of its 144Hz refresh rate. The fluidity and connectedness this provided when gaming was every bit as good as the monitor’s predecessor. Like the earlier models there were signs of inverse ghosting, but this isn’t something most users will find problematic or even notice at all when gaming. This monitor’s real party trick, though, is its ‘Blur Reduction’ feature – which did exactly what it said on the tin. During even the fastest movements on games like Battlefield 4 and Dirt 3 the environment remained clear and sharp. We didn’t find the strobe behaviour of the monitor to be at all problematic despite the scaremongering that’s been going on elsewhere about a certain ‘strobe crosstalk’ issue. Strobe crosstalk exists somewhere on the screen no matter what you do and it’s not something that should bother the majority of users. Don’t let it put you off buying the monitor. If you do have an issue with it once you’ve tried it for yourself there is always the possibility of getting the firmware modified by BenQ so that third party tools can be used to modify the strobe behaviour. This will also allow you to find your own sweet spot between screen brightness and motion blur reduction if you aren’t happy with the factory defaults.

Another real plus for the monitor, again related to the ‘Blur Reduction’ feature, is that the overall image characteristics remain relatively unchanged. If you find some settings you like (be it using an ICC profile or otherwise) with the feature disabled you don’t have to then use a separate configuration when it’s enabled. Things appear dimmer but some users will actually really appreciate that – and your eyes are quite good at adjusting to this change so you may not even notice it after a bit of gameplay. We also thoroughly enjoyed using this operating mode at 100Hz, finding this something of a sweet spot between fluidity (100fps is easier to maintain than 144fps) and image quality on our system. Gaining significantly decreased motion blur compared to native 144Hz operation and richer colours without using ICC profiles is nothing to be sniffed at.

Overall we feel there are plenty of things that could have been done better on this monitor, but plenty of things that could have been done worse. This monitor is designed for gaming – BenQ make no secret of that. The bottom line is that we really enjoyed gaming on this monitor. With ICC profiles employed the image was also quite pleasing on the eyes, even on the desktop where such issues are often more noticeable. If you’re still in a quandary given the mixed reports you may have read on this monitor just remember that everybody is different. We’ve used a heck of a lot of monitors and have engaged with countless users across the gaming spectrum and know that for many this monitor will make for some truly enjoyable gaming.