6 Motion Blur Reduction (MBR)8 Settling behavior8.2 Matrix measurements
|AUO M240HW01 V8|
|MST 8556T (MSTAR)|
|LED (white, edge)|
|MP3398 (Monolithic Power)|
Comparison with other LCDs
The BenQ XL2411Z is more or less identical to the BenQ XL2411T except that it offers a feature called Motion Blur Reduction, BenQ”s alternative to 2D LightBoost. Note that the Z-series monitors still support NVIDIA”s 3D LightBoost, but the Strobelight Utility, which was used to enable 2D LightBoost and also worked with AMD graphics cards, does not work anymore with the Z-series monitors. LightBoost can be still used for 2D, of course, but needs to be enabled with NVIDIA 3D VISION hard- and software.
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LightBoost is only supported for 100 Hz and 120 Hz refresh frequencies, whereas Motion Blur Reduction can be used for frequencies up to 144 Hz.
Regarding image quality, the XL2411Z is also similar if not identical to the XL2420Z. The XL2420Z has just a fancier design, comes with a remote control (not wireless though), and provides more input options (DisplayPort, 2nd HDMI, USB).
Service menu BenQ XL2411Z
Have the monitor connected to a valid signal source. The service menu can be entered by keeping the 2nd button from the left (“down” button) pushed while powering on the monitor. Pushing the 4th button from the left (“menu” button) will then toggle the service menu on and off. In order to access the OSD menu, make the service menu disappear and then push any other but the “menu” button so that the icons above the buttons appear. Then you can push the “menu” button to enter the OSD menu. The “menu” button will react normal again after the next power-on.
As a first in computer monitor”s industry, BenQ offers firmware upgrades for its Z-series monitors. When these monitors were first released they came with a firmware that had a sub-optimal Motion Blur Reduction implementation. This brought BenQ to offer customers to send in such monitors for an upgrade or, as an alternative, allow enthusiasts to do the upgrade themselves (which, however, requires additional programming hardware). See BlurBuster”s firmware upgrade instructions for a step-by-step upgrade how-to. Unfortunately, BenQ does not keep the firmware download page up to date. Currently (mid 2015), monitors are shipped with firmware version 4 which is said to implemented a better overdrive when Motion Blur Reduction is active. As far as the flicker-free mode is concerned, there is no difference between firmware version 2 and 4 though. The results shown below have all been measured with version 2.
Note that, although the XL2411Z as almost identical to the XL2411T, upgrading a BenQ XL2411T with the Z-version firmware would not work (see below, Accessing the backlight signals).
Motion Blur Reduction (MBR)
Motion Blur Reduction (MBR for short) is BenQ”s alternative to 2D LightBoost. Like LightBoost, MBR pulses the backlight once per refresh interval. In contrast to LightBoost, it does so without adopting a special LC panel update timing and without using different overdrive parameters for the different pixel lines, both of which should affect settling behavior negatively. That is, LightBoost has the higher potential to get things right.
MBR features at a glance
On the other hand, BenQ offers more options regarding MBR, at least with firmware version v2. Besides letting the user activate MBR at frequencies other than 100 Hz and 120 Hz and without requiring specific NVIDIA graphics hardware, it is also possible to tweak the backlight pulse parameters, like the pulse width and the pulse phase with respect to VSync in great detail. This is possible either via the service menu (parameters strobe duty and strobe phase), or with BlurBuster”s Strobe Utility, or via direct DDC/CI programming (Display Data Channel/Command Interface). Tweaking the pulse parameters is especially useful if the LC panel update is accelerated by tweaking the monitor timing.
Backlight pulse width
|LightBoost 100 Hz||1.88||3|
|LightBoost 120 Hz||1.4||2.25|
|MBR 60 Hz||0.17||5|
|MBR 100 Hz||0.1||3|
|MBR 120 Hz||0.08||2.5|
|MBR 144 Hz||0.07||2.1|
As soon as strobed backlight is used, be it for LightBoost or for MBR, the backlight LED current is increased by a factor of about 1.8 in order to compensate, at least partly, for the time the LEDs are turned off between the pulses.
The pulse width can be controlled either in 10 steps (LightBoost) or in 30 steps (MBR), linearly within the range given in the table. In MBR mode, also the pulse phase can be modified, in steps of approximately a 100th of the refresh cycle time, where a value of 0 makes the backlight pulse onset roughly coincide with the update of the first pixel line. The maximal value is 100 which suggests that the pulse onset can be arbitrarily chosen anywhere within the refresh cycle. Unfortunately, this is not the case as the pulse phase is limited to a value that makes the pulse offset (not onset!) coincide with a time shortly before the first pixel line is updated. In other words, the update of the first pixel line occurs either before or after the backlight pulse, but cannot occur during the pulse.
Monitor timing (tweaking it)
As mentioned above, the monitor timing can be tweaked in order to speed up the update process of the LC panel. This is done by virtually making the vertical synchronization phase longer while preserving the vertical refresh rate, as described in the guide to the aforementioned BlurBuster”s Strobe Utility. For 120 Hz, the maximal possible total number of vertical lines is 1350, for 100 Hz it is 1500 (empirical findings). These timing modes push the limits regarding pixel clock frequency and it might be worthwhile reducing the total number of pixel columns from 2080 to 2020 in order to lower the line and pixel clock frequencies. Depending on the graphics card it might be necessary to use different sync polarities and within-sync timing values (back porch, front porch, sync duration) in order to make the monitor accept the unconventional timing. It is not fully clear yet, whether at all or in how far the image quality depends on the sync timings. It should be noted though, that whenever the monitor timing deviates too much from any standard timing – which is clearly the case for the timings mentioned here –, the monitor adopts the 60 Hz backlight pulse widths. This is somewhat problematic as it allows to choose pulse durations which could shorten the lifetime of the LEDs. At 120 Hz, for example, the pulse width can be set to 5 ms, which is the intended maximum for 60 Hz though and, thus, pushes the average LED current at 120 Hz way beyond the limit considered safe by the manufacturer. Moreover, the tweaked monitor timings might not work at all (i.e., black screen) if the value for the pulse phase is too high. So, know what you are doing! If, by some mishap, the monitor stays black and does not revert back to a working mode by itself anymore, the only way to disable MBR mode might be to power off the monitor, disconnect it from the power line and possibly even from the computer, let it rest for a while until fully discharged (trying to switch it on in the disconnected state helps with discharging), and then reconnect it again.
By the way, the within-sync timing does not seem to have any effect whatsoever on how long the software blocks when executing the OpenGL SwapBuffers();glFinish() function sequence or when the LC panel is updated (latency). This is the case, at least, with the tested NVidia driver and hardware but, technically, it does not have to be this way. So the behavior might be different with other driver versions or, for example, with AMD graphics cards.
MBR and AMA
AMA is BenQ”s implementation of overdrive and care should be taken when changing the AMA setting before or while in MBR mode. The thing is that the internal overdrive parameters according to AMA=”High” or AMA=”Premium” are changed during the activation of MBR, so there are actually hidden AMA settings “MBR/High” and “MBR/Premium”. However, when changing the AMA setting while already in MBR mode, the MBR-specific overdrive parameters (i.e., according to “MBR/High” or “MBR/Premium”) are overwritten by the parameters normally used in non-MBR mode (i.e., according to “High” or “Premium”). In other words, the order in which to set AMA and to enable MBR mode matters, except for AMA=off which always results in overdrive being shut off.