Cooler Master GM34-CW

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Cooler Master is a brand you might be familiar with in the PC market. They are a computer hardware manufacturer based in Taiwan who have been around since 1992 and are most well known for making PC cases, power supplies and cooling solutions. They are now set to end the PC monitor market, just like manufacturers such as Gigabyte did last year. We are always pleased to see new players appear in this market with new and interesting screen options. Cooler Master’s first venture in to the monitor market is with two displays aimed at gaming – the 34″ ultrawide GM34-CW which we are reviewing here, and the 27″ GM27-CF which we finished reviewing recently.

The GM34-CW is 34″ in size with an ultrawide 21:9 aspect ratio. It features a curved 1500R VA technology panel and has a 3440 x 1440 resolution with a focus on gaming performance and speed. There is a quoted 1ms MPRT spec along with a 144Hz refresh rate. The screen supports adaptive-sync and so supports variable refresh rates (VRR) from both AMD and NVIDIA systems and also includes a blur reduction mode. It also has a wide colour gamut backlight thanks to the use of Quantum Dot coating.

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Specifications and Features

The following table gives detailed information about the specs of the screen as advertised:

The GM34-CW offers a good range of modern connectivity with 2x DisplayPort 1.4, 1x HDMI 1.4 and 1 x HDMI 2.0 offered for video connections. These are located on the back of the screen along with a headphone output. Unlike many screens there are no USB ports on this model. For PC connectivity the DisplayPort is the most common option, with HDMI being available then for connecting external games consoles or Blu-ray players potentially. The screen has an external power supply and the screen also comes packaged with the power cable and brick that you need.

Below is a summary of the features and connections of the screen.

Design and Ergonomics

The GM34-CW comes in a black and dark grey design, with matte plastics used for the bezel and rear enclosure. There is a 3-side borderless design with a thin 2mm black plastic edge to the screen along the sides and top, and then an additional 7.5mm black panel border before the image starts (total edge = 9.5mm). Along the bottom edge is a thicker 16mm bezel and then an additional 3mm black panel border.

The back of the screen is encased in a matte black plastic for a fairly simple and smooth design. The stand connects in to the middle with a quick release mechanism and is a sturdy metal design. It has a dark silver aluminium arm and foot, which is again in the shape of the Cooler Master logo. You have to screw the stand together in a couple of places before it is attached to the screen but that’s simple enough. The back of the screen also features a simple LED lighting feature which glows purple when turned on. You can also set this to flicker in the OSD menu or turn it off altogether, but there are no other colours or settings available.

The stand is pretty strong and sturdy with its metal design. There is a reasonably thin overall profile to the screen, and you can see the screen curvature in the image below.

Above: side view of the screen. Click for larger version

The stand offers a fairly decent range of ergonomic adjustments with tilt, height and swivel provided. Tilt is smooth but quite stiff to move, especially tilting it backwards. Like the 27″ GM27-CF it doesn’t tilt backwards very much so depending on your viewing position the screen itself it can feel a bit upright. We would have liked a bit more flexibility to tilt it backwards. Height adjustment is smooth but also quite stiff. At the lowest setting the bottom edge of the screen is ~40mm from the top of the desk, and at maximum extension it is ~140mm, giving a total 100mm adjustment range as advertised. Side to side swivel is smooth although very stiff, so you often end up moving the whole screen at once. You have to hold the base in place really to swivel the screen side to side. There’s no rotation function offered on this screen as it’s impractical on a curved format display of this size. There is very little wobble to the screen when you move it around which is good, so overall it feels sturdy.

A summary of the ergonomic adjustments are shown below:

The materials were of a reasonable standard and the build quality felt ok. There was no audible noise from the screen, even when conducting specific tests which can often identify buzzing issues. The whole screen remained cool even during prolonged use.

The OSD is controlled entirely through 4 pressable buttons on the bottom right edge of the screen. There is also a power on/off button located next to them. The menu is split in to 9 sections down the left hand side, with available options then shown in the middle and right hand columns. There’s plenty of settings to play around with in the menu which gives a good amount of configuration control. Navigation was mostly ok although a bit sluggish sometimes. We did also find ourselves accidentally switching the screen off a few times instead of exiting out of a section  which was annoying.

Panel and Backlighting

Backlight dimming at calibrated brightness setting (no PWM)

Above: backlight operation showing constant Direct Current voltage instead of PWM. Measured at calibrated brightness level

Brightness and Contrast

This section tests the full range of luminance (the brightness of the screen) possible from the backlight, while changing the monitors brightness setting in the OSD menu. This allows us to measure the maximum and minimum adjustment ranges, as well as identify the recommended setting to reach a target of 120 cd/m2 for comfortable day to day use in normal lighting conditions. Some users have specific requirements for a very bright display, while others like a much darker display for night time viewing or in low ambient light conditions. At each brightness level we also measure the contrast ratio produced by the screen when comparing a small white sample vs. a black sample (not unrealistic full screen white vs. full screen black tests). The contrast ratio should remain stable across the adjustment range so we also check that.

Graphics card settings were left at default with no ICC profile or calibration active. Tests were made using an X-rite i1 Display Pro Plus colorimeter. It should be noted that we used the BasICColor calibration software here to record these measurements, and so luminance at default settings may vary a little from the LaCie Blue Eye Pro report you will see in other sections of the review.

At the full brightness setting in the OSD the maximum luminance reached a high 484 cd/m2 which was a fair bit higher even than the 400 cd/m2 max brightness spec from the manufacturer. There was a decent 423 cd/m2 adjustment range in total, so at the minimum setting you could reach down to a luminance of 62 cd/m2. This should afford you a low luminance option for working in darkened room conditions with low ambient light. A setting of ~13 in the OSD menu is suggested to return you a luminance as close to 120 cd/m2 as possible at default settings.

We have plotted the luminance trend on the graph above. The screen behaves as it should in this regard, with a reduction in the luminance output of the screen controlled by the reduction in the OSD brightness setting. The average contrast ratio of the screen was measured at 3025:1 which was excellent thanks to the VA technology panel.

Testing Methodology

An important thing to consider for most users is how a screen will perform out of the box and with some basic manual adjustments. Since most users won’t have access to hardware colorimeter tools, it is important to understand how the screen is going to perform in terms of colour accuracy for the average user.

We restored our graphics card to default settings and disabled any previously active ICC profiles and gamma corrections. The screen was tested at default factory settings using our new X-rite i1 Pro 2 Spectrophotometer combined with LaCie’s Blue Eye Pro software suite. An X-rite i1 Display Pro Plus colorimeter was also used to verify the black point and contrast ratio since the i1 Pro 2 spectrophotometer is less reliable at the darker end.

Targets for these tests are as follows:

  • CIE Diagram – confirms the colour space covered by the monitors backlighting in a 2D view, with the black triangle representing the displays gamut, and other reference colour spaces shown for comparison. Usually shown as a comparison against the common sRGB space
  • Colour space coverage volumes – we also measure using a piece of software called ChromaPure the colour space (gamut) volumes produced by the backlight in comparison to the sRGB, DCI-P3 and Rec.2020 colour spaces. sRGB is the most commonly used colour space so it is important to have a decent coverage from the screen here. If the colour space is >100% sRGB then the screen can produce a wider colour gamut, often reaching further in to the wider gamut DCI-P3 (commonly used for HDR) and Rec.2020 reference spaces.
  • Gamma – we aim for 2.2 which is the default for computer monitors
  • Colour temperature / white point – we aim for 6500k which is the temperature of daylight
  • Luminance – we aim for 120 cd/m2, which is the recommended luminance for LCD monitors in normal lighting conditions
  • Black depth – we aim for as low as possible to maximise shadow detail and to offer us the best contrast ratio
  • Contrast ratio (static) – we aim for as high as possible. Any dynamic contrast ratio controls are turned off here if present
  • dE average / maximum – we aim for as low as possible. If DeltaE >3, the color displayed is significantly different from the theoretical one, meaning that the difference will be perceptible to the viewer. If DeltaE <2, LaCie considers the calibration a success; there remains a slight difference, but it is barely undetectable. If DeltaE < 1, the color fidelity is excellent.

Default Performance and Setup

Default settings of the screen were as follows:

Out of the box the screen was set in the ‘warm’ colour temp preset mode and with a very bright 90% brightness which was uncomfortable to use for long periods. You will want to turn that down as with most screens. The colour temperature felt a bit warm out of the box and you could tell that the screen was using a wide gamut backlight, as the colours looks vivid and bright, especially greens and reds. We went ahead and measured the default state with the i1 Pro 2. The CIE diagram on the left of the image confirms that the monitors colour gamut (black triangle) extends a considerable way beyond the sRGB reference space (orange triangle), mostly in green and red shades. We measured using ChromaPure software a 137.5% sRGB gamut volume coverage which corresponds to 101.4% of the DCI-P3 reference and 72.7% of the Rec.2020 reference. This is a little over the specified 125% sRGB / 95% DCI-P3 even which was pleasing. There is no sRGB emulation mode available on this screen unfortunately, so no way to reduce the colour gamut if you wanted to specifically work with smaller standard gamut content. The wider gamut here with more vivid and saturated colours is nice for gaming which is the screen’s primary target usage, but keep in mind the limitation if you are wanting to do any colour critical work with sRGB content.

Default gamma was recorded at 2.2 average with a small 1% overall deviance from the target, although you can see the gamma is a bit high in darker tones and a bit low in lighter tones. White point was too warm by 11% being measured at 5789k, although the screen was set in the ‘warm’ mode out of the box and that should be easy to correct through some OSD changes.

Luminance at the default high 90% brightness level was recorded at 449 cd/m2 which is a far too high for prolonged general use, you will need to turn that down a lot. The black depth was 0.15 cd/m2 at this default brightness setting, giving us an excellent 3043:1 contrast ratio which is an obvious strength of this panel, and thanks to the use of VA technology. Colour accuracy measurements are comparing the produced wider gamut display colours against an sRGB reference which will always lead to differences. There was no sign of any colour banding when testing gradients which was good news, and only minor amounts of gradation in darker tones evident.

Optimal Settings Pre-Calibration

We also measured the screen after adjusting only the OSD controls, to obtain the optimal setup without a full calibration, and without the use of an ICC correction profile. This represents what could be achieved through just simple changes to the monitor itself, and also what you could expect when working with content outside of an ICC profile managed workflow. The early stages of our calibration software helped identity these optimal OSD settings.

For this section we switched to the ‘User’ colour temp mode, which would allow us access to the RGB controls and therefore the ability to correct the white point which was now more closely met. The brightness adjustment also allowed us to reach a much more comfortable level. The contrast ratio was still excellent here at 3076:1.

These optimal settings helped the screen look a lot better than out of the box, especially correcting the gamma and brightness. Further calibration and profiling below will help improve things even further in the next section. The dE measurements should be ignored as they are comparing the produced wide gamut colours against an sRGB reference.


We used the X-rite i1 Pro 2 Spectrophotometer combined with the LaCie Blue Eye Pro software package to achieve these results and reports. An X-rite i1 Display Pro Plus colorimeter was used to validate the black depth and contrast ratios due to lower end limitations of the i1 Pro device.

The OSD settings were adjusted as shown in the table above, as guided during the calibration process and measurements. These OSD changes allowed us to obtain an optimal hardware starting point and setup before software level changes would be made at the graphics card level. We left the  LaCie software to calibrate to “max” brightness which would just retain the luminance of whatever brightness we’d set the screen to, and would not in any way try and alter the luminance at the graphics card level, which can reduce contrast ratio. These adjustments before profiling the screen would help preserve tonal values and limit banding issues. After this we let the software carry out the LUT adjustments and create an ICC profile.

The default gamma curve had been only 1% out overall from a 2.2 average, although the profiling here had helped improve the curve across grey shades nicely. The white point was also now improved to 6478k which was great news, and corrected the 11% deviance we’d seen out of the box where it was too warm. The brightness control adjustment had reduced the luminance to a comfortable level now and contrast ratio remained excellent thanks to the VA panel. Colour accuracy of the resulting profile was very good, with dE average of 0.6 and maximum of 2.0. LaCie would consider colour fidelity to be very good overall. Gradients remained smooth with only minimal gradation in darker tones.

You can use our settings and try our calibrated ICC profile if you wish, which are available in our ICC profile database. Keep in mind that results will vary from one screen to another and from one computer / graphics card to another.

Setup Comparisons

The comparisons made in this section try to give you a better view of how each screen performs, particularly out of the box which is what is going to matter to most consumers. We have divided the table up by panel technology as well to make it easier to compare similar models. When comparing the default factory settings for each monitor it is important to take into account several measurement areas – gamma, white point and colour accuracy. There’s no point having a low dE colour accuracy figure if the gamma curve is way off for instance. A good factory calibration requires all 3 to be well set up. We have deliberately not included luminance in this comparison since this is normally far too high by default on every screen. However, that is very easily controlled through the brightness setting (on most screens) and should not impact the other areas being measured anyway. It is easy enough to obtain a suitable luminance for your working conditions and individual preferences, but a reliable factory setup in gamma, white point and colour accuracy is important and some (gamma especially) are not as easy to change accurately without a calibration tool.

From these comparisons we can also compare the calibrated colour accuracy, black depth and contrast ratio. After a calibration the gamma, white point and luminance should all be at their desired targets.

Default setup of the screen out of the box was moderate. It had a decent gamma curve at least which was good, and a high static contrast ratio thanks to the VA panel. There was also a wide colour gamut covering ~137% of the sRGB reference space so you had nice bright and vivid colours. The white point / colour temperature was a little too warm, although easy to correct through some basic OSD adjustments. There was unfortunately no sRGB emulation mode so you were stuck with the full wide gamut all the time, which might not be ideal if you wanted to do any colour critical work. Contrast remains very strong after calibration as well.

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Viewing Angles

Viewing angles of the screen were a bit weaker than we’d seen from other recent VA panels, although still offering something in the middle between the wide viewing angles of IPS technology, and the poor viewing angles of TN Film. There was a pinkish hue introduced from wider viewing angles from the side, and the image became quite washed out at the more extreme angles. Vertical viewing angles showed washout and gamma shift as you can see above. The 27″ GM27-CF had offered better, more stable viewing angles when we tested it recently. A lot of Samsung VA panels tested recently seemed to offer improved viewing angles compared with AU Optronics’ equivalent VA technology. Here on the GM34-CW they looked a bit more like AUO models such as the Asus ROG Swift PG35VQ for instance.

Users should also be aware that the panel exhibits the off-centre contrast shift which is inherent to the VA pixel structure. When viewing a very dark grey font for example on a black background, the font almost disappears when viewed head on, but gets lighter as you move slightly to the side. This is an extreme case of course as this is a very dark grey tone we are testing with. Lighter greys and other colours will appear a little darker from head on than they will from a side angle, but you may well find you lose some detail as a result. This can be particularly problematic in dark images and where grey tone is important. It is this issue that has led to many graphics professionals and colour enthusiasts choosing IPS panels instead, and the manufacturers have been quick to incorporate this alternative panel technology in their screens. We would like to make a point that for many people this won’t be an issue at all, and many may not even notice it. Remember, many people are perfectly happy with their TN Film panels and other VA based screens. Just something to be wary of if you are affected by this issue or are doing colour critical work.

On a black image from a side view there is very little glow from the panel, and the deep blacks and strong contrast ratio are still evident. You don’t get the same pale/white glow that IPS-type panels exhibit (example the Asus TUF Gaming VG27AQ with IPS-type panel) which is a big plus for this panel technology, especially if you want to use the screen for night time gaming or movies in a darker room. There are some uniformity problems on this sample when viewed in this way, which is something we’d seen on other recent VA panels too including the very expensive ROG Swift PG35VQ. You can see some areas of backlight glow and blotchiness on this kind of test particularly at the top. Again these results were pretty similar to the 27″ GM27-CF as well as recently tested Samsung C27RG50 and Samsung C49RG90 for instance which feature VA panels as well.

Panel Uniformity

We wanted to test here how uniform the brightness was across the screen, as well as identify any leakage from the backlight in dark lighting conditions. Measurements of the luminance were taken at 36 points across the panel on a pure white background. The measurements for luminance were taken using BasICColor’s calibration software package, combined with an X-rite i1 Display Pro colorimeter with a central point on the screen calibrated to 120 cd/m2. The below uniformity diagram shows the difference, as a percentage, between the measurement recorded at each point on the screen, as compared with the central reference point.

It is worth noting that panel uniformity can vary from one screen to another, and can depend on manufacturing lines, screen transport and other local factors. This is only a guide of the uniformity of the sample screen we have for review.

Uniformity of Luminance

Luminance uniformity of the screen was quite good overall on our sample, with 71% of the screen within a 10% deviance of the centrally calibrated area. The right and left hand edges were a little darker than the central areas of the screen where brightness dropped down to 93 cd/m2 in the most extreme example (-29%).

Backlight Leakage

We also tested the screen with an all black image and in a darkened room. A camera was used to capture the result. There was a little bit of leakage from the top and bottom edges, but it was very slight and not something you’d see in normal usage at all. You also had nice deep blacks thanks to the high contrast ratio VA panel.

Note: if you want to test your own screen for backlight bleed and uniformity problems at any point you need to ensure you have suitable testing conditions. Set the monitor to a sensible day to day brightness level, preferably as close to 120 cd/m2 as you can get it (our tests are once the screen is calibrated to this luminance). Don’t just take a photo at the default brightness which is almost always far too high and not a realistic usage condition. You need to take the photo from about 1.5 – 2m back to avoid capturing viewing angle characteristics, especially on IPS-type panels where off-angle glow can come in to play easily. Photos should be taken in a darkened room at a shutter speed which captures what you see reliably and doesn’t over-expose the image. A shutter speed of 1/8 second will probably be suitable for this.

General and Office Applications

One of the key selling points of ultra-wide screens like the this is it’s high resolution and large screen size. The 3440 x 1440 display offers a sharp but comfortable picture. Its pixel area is about 1.8 times larger than an Ultra-Wide Full HD 21:9 monitor, and about 2.4 times larger than a Full HD 16:9 monitor. It provides an efficient environment in using Microsoft Office programs showing 47 columns and 63 rows in excel. Thankfully the high resolution is of a very comfortable size on the 34″ panel, with a 0.2325mm pixel pitch is is very comparable to a 27″ 2560 x 1440 monitor (0.2331mm). This means you are basically getting a wider desktop to work with, with a similar font size to a 27″ model, and maintaining the same vertical resolution as well. If you’re coming from a lower resolution / larger pixel pitch you may still find the fonts look quite small to start with, but like the 27″ 1440p models out there you soon get used to it. Side by side multi-tasking on this screen is excellent and you really do have a nice wide area to work with. We liked the curved format of the display actually for day to day office work. It just felt a bit more comfortable than a flat screen on a model as wide as this, bringing the corners a bit nearer to you. You didn’t really notice the curve in normal use but we liked the feel. Probably down to user taste, so if in doubt try and see one in person.

The light AG coating of the VA technology panel is certainly welcome, and avoids any unwanted graininess to the image. The wide viewing angles provided by this panel technology on both horizontal and vertical planes, helps minimize on-screen colour shift when viewed from different angles. There is the typical VA off-centre contrast shift though which might crush dark grey details on darker content when viewed head on. So it’s not as well suited to colour critical work or photo editing as an IPS technology panel. But it is on the other hand much better than a TN Film panel.

The out of the box setup was fairly good for these uses with at least a reliable gamma setup. The colour temperature was a bit warm but easy to correct from the OSD menu and actually you may want it a bit warmer for office work anyway. Thanks to the VA panel there was a strong contrast ratio. One issue for general use is that the screen does not offer any sRGB emulation mode, it will only operate with the full gamut of the backlight (in this case 137.5% sRGB). This gives you more vivid and saturated colours which can look attractive for gaming and multimedia, but could present a problem if you’re working with standard sRGB gamut content. We would have liked to see an sRGB emulation mode available for those who are doing colour critical work or photo editing and working with this smaller colour space.

The brightness range of the screen was good, with the ability to offer a luminance between 484 and 62 cd/m2. This should afford you a decent enough range for darkened room conditions and low ambient light. A setting of around 13 in the OSD brightness control should return you a luminance close to 120 cd/m2 out of the box. The brightness regulation is controlled via a flicker free backlight, without the need for Pulse Width Modulation (PWM), and so those who suffer from eye fatigue or headaches associated with flickering backlights need not worry. There was no audible noise from the screen, even when conducting specific tests which can sometimes cause issues.

As shown above, the Cooler Master website talks about how the screen features a Quantum Dot coating and offers a wide colour gamut. It does indeed use Quantum Dot coating, and the colour space is actually even wider than they advertise (137.5% sRGB measured as opposed to 125%). They also talk about how the blue spectral peak is at 466.8 nW/nm wavelength which is supposed to be better for your eyes than a typical blue light wavelength of LED monitors of 450 nW/nm. We wanted to measure this for ourselves:

Spectral distribution graph showing calibrated mode at 6500k

At our calibrated 6500k colour temperature you can see a fairly typical spectral output for a Quantum Dot screen. However the blue wavelength seems to be at the normal 450 nW/nm level unfortunately.

Spectral distribution graph showing Low Blue Light set at 50

Spectral distribution graph showing Low Blue Light set at 100

There are some low blue light filter settings available in the OSD menu with 4 modes available at 25, 50, 75 and 100. The colour temperature gets warmer as you increase the setting, and the blue light output is reduced as you do so. At 50% the  white point was 5243k and felt pretty comfortable to use. At 75% it was 4775k and at 100% the colour temp is now 4455k and looks too warm really, unless you are perhaps doing a lot of text work.

Unusually for a modern display there are no USB ports provided on this screen. There are no other extras like motion sensors or card readers on this screen which are sometimes useful for office-type uses. There is a reasonable range of ergonomic adjustments from the stand with tilt, height and swivel offered. There is also VESA 75mm mounting capabilities for those who want to mount the screen instead.

Responsiveness and Gaming

The screen uses overdrive technology to boost pixel transitions across grey to grey changes as with nearly all modern displays. The part being used is a Samsung LSM270HP09 SVA (VA-type) technology panel with a custom backlight. Have a read about response time in our specs section if you need additional information about this measurement.

We use an ETC M526 oscilloscope for these measurements along with a custom photosensor device. Have a read of our response time measurement article for a full explanation of the testing methodology and reported data.

Response Times and Refresh Rate

There’s various things you need to consider when it comes to response times and gaming, particularly on a display with high refresh rate support. Gaming screens invariably give you a control for the overdrive impulse in the OSD menu which can help you tweak things, but response time performance and overshoot levels can vary depending on the active refresh rate. This behaviour is often different depending on whether the screen is a traditional G-sync screens (with hardware module) or whether it’s an adaptive-sync screen as well, and not all screens behave in the same way. We always try to test each variable in our reviews but the key considerations you need to make are:

  1. Performance at 60Hz – this is important if you want to use an external games console (or other device like a Blu-ray player etc) which typically run at 60Hz. Response time performance may well be different than at the higher refresh rates supported, and you may need a different overdrive setting for optimal experience.
  2. Performance during VRR (Variable Refresh Rate) – bearing in mind that the refresh rate will fluctuate anywhere from 1Hz up to the maximum supported by the screen (e.g. 1 – 144Hz on a 144Hz display). It’s important to understand if the response times and overshoot will vary as the refresh rate changes. There may be a need to switch between different overdrive settings in some cases, depending on your usually attained refresh rate output and graphics card capability. This can sometimes become fiddly if your refresh rates fluctuate a lot, especially between different games, so it’s always easier if you can leave a display on a single overdrive setting which is suited to the whole range. Some screens also feature “variable overdrive” which helps control the response times and overshoot depending on the active refresh rate. This is particularly apparent with traditional G-sync module screens.
  3. Performance at fixed refresh rates including maximum – this is important for those who have a powerful enough system to consistently output a frame rate to meet the max refresh rate capability of the screen. They may want to run at max refresh rate without VRR active, or even is VRR is active they may know they will be consistently at the upper end of the range. Many gaming screens show their optimal response time performance at the maximum refresh rate. Knowing the performance at high fixed refresh rates may also be applicable if you want to use any added blur reduction backlight which typically operate at a fixed refresh rate.
  4. Whether the response times can keep up with the frame rate – you will also want to consider whether the response times of the panel can consistently keep up with the frame rate. For instance a 144Hz screen sends a new frame to the display every 6.94ms, so the pixel response times need to ideally be consistently and reliably under this threshold. If they are too slow, it can lead to added blurring in practice and sometimes make the higher refresh rates unusable in real life. We consider this in our analysis.

We carried out some initial response time measurements and visual tests in each of the overdrive settings, and at a range of refresh rates. The overdrive control is available in the OSD menu via the ‘Response Time Override’ option. There are 4 levels available – Off, Normal, Fast and Fastest. Oddly they are in a weird order in the menu here.

Increasing Refresh Rate

We quickly established that using even the ‘Fast mode was optimal on this screen. It didn’t introduce any obvious halos or overshoot artefacts in motion tests and offered some improvements in motion clarity and blurring compared with the lower modes. The maximum ‘Fastest’ mode produced a bit of noticeable dark trailing in motion tests, and looked to be a little too aggressive. We tested the response times at a range of refresh rates from 60Hz up to the maximum native 144Hz. You can see that the screen actually uses variable overdrive here which is good news, a feature normally reserved for Native G-sync hardware screens and rarely used on adaptive-sync displays as it is quite hard to get working and configured. The response times therefore improved as the refresh rate was increased, helping them to keep up better with the higher frame rate demand which was good news. We had seen the same thing from the Cooler Master GM27-CF 27″ model, so it’s nice to see it included here as well.

The response times overall were very good for a VA panel, with 5.6ms G2G measured at 144Hz for instance if we ignore the usual problematic slow black > grey transitions that plague most VA panels and are shown along the top row of the tables above. While other transitions were sped up nicely to support the higher refresh rates, these black > dark grey transitions were still an issue as with most VA panels and leads to some black smearing on moving content, particularly on darker backgrounds. The higher refresh rates did improve the motion clarity significantly though compared with 60Hz, as these higher refresh rates have a direct impact on how the human eye perceives motion on LCD displays. There was a bit of measured overshoot recorded here too. Some more detailed measurements in a moment will provide a better indication of the level of VA black smearing and response time / overshoot behaviour.

Variable Refresh Rates (VRR)

The screen supports VESA Adaptive-sync and so can support variable refresh rates from compatible AMD FreeSync and NVIDIA G-sync systems. The VRR range supported is between 48 and 144Hz . The screen has not currently been certified by NVIDIA under the ‘G-sync Compatible’ scheme. The Cooler Master website lists the screen as being FreeSync 2 certified which is AMD’s older certification scheme, but means the screen has verified VRR performance, support for an HDR input signal and Low Framerate Compensation (LFC).

The support for G-sync and FreeSync will be very useful given the significant system demands of running a screen at 3440 x 1440 resolution and up to 144Hz refresh rate. It was of course very good to see it included here. You might also want to read our newly updated article about Variable Refresh Rates here for more information.

Detailed Response Times

To achieve the optimal performance from the GM34-CW we would recommend sticking with the ‘Fast’ response time setting. This looked a bit clearer and sharper than the lower modes, and didn’t introduce anything too noticeable in the way of overshoot or halos. It was great to see the use of variable overdrive for refresh rates up to 144Hz as well, helping to optimise performance and keep up with the increasing frame rates. This also meant you could stick with a single setting for all refresh rates and for VRR, making it much easier than many other adaptive-sync screens. The higher refresh rates supported by the screen really do help improve motion clarity and reduce perceived  blur, making the screen far better for gaming than 60Hz-only models.

Recommended Settings

Optimal Refresh Rate 144Hz
Optimal Overdrive Setting (for above) Fast
Optimal Overdrive Setting for 60Hz Fast
Optimal Overdrive Setting for VRR Fast

     Detailed Measurements at 144Hz, Overdrive = Fast

We carried out some further response time measurements at 144Hz. We measured an average 7.0ms G2G response time in this mode which was good overall for a VA panel, and that includes the couple of particularly slow black > dark grey transitions along the top row that are nearly always a problem for VA panels. Those few very slow transitions lead to some black smearing in practice, but actually here on the GM34-CW it was at a reasonably low level (rated 40%) as it only impacted the black to dark grey changes, not the black to light grey changes. We will compare this more with other VA screens in a moment. If we were to ignore those problem transitions then the average response time would be 5.4ms G2G which was impressive and very good for a VA technology screen. The best case even reached down to 1.5ms G2G which was excellent, albeit introducing some overshoot in doing so.

There were mostly low levels of overshoot measured at this Fast mode with a couple of instances where it was measured at a higher level, although there were few obvious overshoot artefacts in practice. You might see a bit of overshoot in some cases, but we felt this mode was still very useable. That bit of overshoot is the trade-off here for some pretty decent response times in general. In fact 73.3% of them were fast enough to keep up with the 144Hz refresh rate which was pleasing (76.7% with a 1ms leeway included), meaning there was not much additional response time smearing caused by their inability to keep up with the frame rate.

Refresh Rate Compliance

In this section we look at the response time behaviour across the range of supported refresh rates and consider whether they are sufficient to keep up with the frame rate demands of the screen. The grey line on the graph shows the refresh rate threshold, that being the average G2G response time that the panel needs to be able to achieve to keep up properly with the refresh rate and frame rate. For instance at a 60Hz refresh rate the response times need to be consistently and reliably under 16.67ms, while at 144Hz refresh rate the response times ideally need to be under 6.94ms to keep up with the frame rate demands. If they are not then this can lead to some additional smearing and blurring on moving content as the pixels can’t keep up. For these tests we will plot the average G2G figure at a range of measured refresh rates, while operating at the optimal overdrive control.

The table to the right then explains whether that overdrive control needs to be adjusted by the user depending on the refresh rate (not ideal), or whether variable overdrive is utilised to keep things simple. Ideally you’d want to be able to stick with a single mode for all refresh rates especially when you consider how these will vary during VRR. We also include a measurement of the % of the overall response time measurements that were within the refresh rate, as well as a slightly more lenient measurement of how many were within the refresh rate window within a 1ms leeway.

It’s a little tricky to plot these graphs for VA panels as if you consider the overall average response time it gets affected by the few particularly slow black > grey transitions that cause problems on this technology. To give a fairer picture here we have used the average G2G figure if those few problem transitions were ignored, but keep in mind that those are still there and cause some black smearing in moving content as on most VA panels. You can see that overall the compliance with the refresh rate was good on this panel. Variable overdrive helped ensure that response times were improved as the refresh rate increased, so that the panel could keep up with the higher frame rate demands. That’s rare to see used on an adaptive-sync screen so it was great to see it offered here. The overshoot did creep up a bit as the refresh rate increased, but never reached particularly noticeable levels we didn’t feel and was still good overall.

Motion Blur Reduction (MPRT mode)

The strobing blur reduction backlight option is available via the ‘MPRT’ (Motion Picture Response Time) setting which is available in the OSD. You would only want to enable MPRT mode for gaming as it introduces a deliberate strobing flicker to the screen which is not what you want for day to day office-type uses. For gaming these blur reduction backlights can normally help improve the perceived motion clarity and make gaming even better.

Example strobing at 144Hz, horizontal scale = 5ms

This MPRT mode is only available at fixed refresh rates of 100, 120 and 144Hz (not at 60Hz). Like nearly all other blur reduction modes except a few Asus ‘ELMB-sync’ models such as the Asus TUF Gaming VG279QM tested recently, this feature cannot be used at the same time as FreeSync/G-sync variable refresh rates, it’s one or the other. The strobing is in sync with the refresh rate of the display, so at 144Hz the screens backlight is turned on/off again every 6.94ms. With MPRT enabled some settings are unfortunately locked in the OSD. Brightness is locked which means you can’t customise the brightness of the display, you are locked at a luminance of each mode. If you change the brightness setting it just turns the blur reduction mode off.

The MPRT mode has 3 settings though for normal, fast and fastest. Each mode reduces the strobe “on” period slightly more than the last, which should help sharpen up the image in theory and improve motion clarity. It also directly impacts the brightness of the screen. In normal mode the brightness of the screen was 313 cd/m2. In fast mode it was 190 cd/m2 and in fastest mode it was 97 cd/m2. The middle ‘fast’ mode was probably the most comfortable mode brightness-wise to use. The ‘Fastest’ mode didn’t really offer any improvements in motion clarity either which is examined in more detail in a moment.

Maximum Blur Reduction Brightness – Display Comparison

We include this section here only for completeness. For ease of reference we have also provided a comparison table below of all the blur reduction enabled displays we’ve tested, showing their maximum luminance before blur reduction is turned on (normal mode) and their maximum luminance with the feature enabled. This will give you an idea of the maximum brightness you can expect from each model when using their blur reduction feature, if that is important to you. A lot of people want a brighter display for gaming and sometimes the relatively low maximum luminance from blur reduction modes is a limitation.

These comparisons are with the refresh rate as high as is available for the blur reduction feature to function. For most this is at 100 – 144Hz. You can often achieve a slightly brighter display if you use the feature at compatible lower refresh rates since the strobes are less frequent, but it’s not a significant amount. That can also introduce more visible flicker in some situations.

Note: Pulse Width setting at max where applicable.
*Note 2: The Acer XB270HU was later updated to include a 120Hz mode, which will produce a slightly darker maximum luminance

Blur Reduction Tests

Of course the main thing we want to test is what improvements the Blur Reduction mode offers when it comes to motion clarity and gaming. The following pursuit camera photos give you an indication of observed motion clarity as the human eye would see it at the top, middle and bottom areas of the screen.

Pursuit camera photos capturing perceived motion clarity in the central region at 144Hz refresh rates, MPRT mode = Fast

The Fast MPRT mode provided the best setting we felt, being a comfortable brightness for a start. Unfortunately on this screen you get a high level of strobe cross talking and ghosting on moving images. The UFO itself is sharper, but the trailing images are distracting and it makes it hard to really use this mode sadly. This is the same in the other modes too.

Gaming Comparisons

We have provided a comparison of the display against many other gaming screens we have reviewed in a similar size range and across a range of panel technologies. This table is now split by panel technology to make life a bit easier and for quicker comparison.

The GM27-CF had decent overall response times for a VA panel, being able to keep up with the high refresh rates well, and delivering good motion clarity. There was some usual VA black smearing which was a shame, although at a slightly lower level than many VA panels as you can see below (40% rating). This is something you generally have to live with on any VA monitor. The TN Film and IPS models are faster options for gaming and don’t suffer from those slow black > grey transitions. Although you do then give up things like the much higher contrast ratio that VA tech can offer.

VA Technology Display Comparison

To try and give a more direct comparison between the different VA models we’ve tested we have produced the following new comparison table below. Each screen is set to the optimal response time setting and refresh rate from our reviews.

The GM34-CW has a slightly lower level of black smearing at 40% than many other models here which was good news. It’s still evident on black to dark grey transitions, but paler transitions are faster than some other models. Overall this results in less noticeable black smearing in practice. The response times were very good too for a VA panel (ignoring the slow black > dark grey transitions here keep in mind) although some moderate overshoot was the trade-off to achieve that.

Additional Gaming Features

  • Aspect Ratio Control – the screen offers a range of aspect ratio controls from the menu including wide screen, 4:3, 1:1 pixel mapping and an ‘auto’ mode. This gives a good range of support for other non-native inputs.
  • Preset Modes – There aren’t really any preset modes on this screen apart from one called simply “game”. This has quite a few settings locked and unavailable though so you will probably be better sticking to the standard mode and calibrating it to your liking.
  • Additional features– there is a crosshair graphic option in the menu, but no other gamer-oriented features to note.


Read our detailed article about input lag and the various measurement techniques which are used to evaluate this aspect of a display. The screens tested are split into two measurements which are based on our overall display lag tests and half the average G2G response time, as measured by our oscilloscope. The response time element, part of the lag you can see, is split from the overall display lag and shown on the graph as the green bar. From there, the signal processing (red bar) can be provided as a good estimation of the lag you would feel from the display. We also classify each display as follows:

Lag Classification

  • Class 1) Less than 8.33ms – the equivalent to 1 frame lag of a display at 120Hz refresh rate – should be fine for gamers, even at high levels
  • Class 2) A lag of 8.33 – 16.66ms – the equivalent of one to two frames at a 120Hz refresh rate – moderate lag but should be fine for many gamers. Caution advised for serious gaming
  • Class 3) A lag of more than 16.66ms – the equivalent of more than 2 frames at a refresh rate of 120Hz – Some noticeable lag in daily usage, not suitable for high end gaming

The total lag measured was a decent 6.40ms. The pixel response times should account for around 2.70ms, and so we can say that there appears to be around 3.70ms of signal processing lag on this screen which is low. A solid result from this display and making it suitable for fast and competitive gaming.

Movies and Video

The following summarises the screens performance for videos and movie viewing:

CategoryDisplay Specs / MeasurementsComments
Size34″ ultrawideLarge for a desktop monitor currently
Aspect Ratio21:9A lot of content and devices might not be set up for this wide format, and so you may end up with black bars down the right and left hand sides, particularly for common 16:9 input sources
Resolution3440 x 1440Can support native 1080p content but not Ultra HD 4K natively
HDCPYes v2.2Suitable for encrypted content
Connectivity2x DisplayPort 1.4
1x HDMI 2.0
1x HDMI 1.4
Useful additional 2x HDMI input for external Blu-ray players or games consoles
CablesDisplayPort onlyNot provided with an HDMI cable in the box
ErgonomicsTilt, height. swivelGood set of adjustments suitable to positioning the screen in a variety of angles for different viewing positions. Tilt doesn’t move backwards very much and most movements are stiff
CoatingLight Anti-glareProvides clear, non-grainy image and avoids unwanted reflections of full glossy solutions
Brightness range62 – 484 cd/m2Good adjustment range offered including a high peak brightness. Flicker free backlight operation with no PWM
Contrast3057:1 after calibrationVery good VA contrast ratio which should be great for dark content and offering good shadow detail.
Preset modesMovieThere is a movie mode available which has a lot of locked settings, but may be useful if you want to set something a bit brighter for movie viewing for instance
Response times7.0ms G2G, low overshoot at 144Hz 9.5ms G2G at 60Hz with low overshootResponse times are mostly very good for a VA panel especially at the higher refresh rates. There is the typically slow black > grey VA technology transitions and some black smearing on moving content as a result, particularly darker content. This is at a lower level than many other VA panels though. At 60Hz the response times are slower but adequate, with low overshoot.
Viewing anglesGoodNot as wide as IPS, and fairly typical for a VA panel. Free from the pale “IPS-glow” on dark content when viewed from an angle that you see on IPS panels but do suffer from the black crush when viewed head on. May lose some detail in darker scenes as a result
Backlight bleedNo major bleedSome slight leakage along top and bottom but hard to see during normal use
AudioHeadphone output and 2x 3W speakersBasic integrated speakers on this model which might be ok for the occasional YouTube clip or mp3 and are reasonable quality. A headphone jack is also provided
Aspect Ratio ControlsWidescreen, 4:3, 1:1 and auto modesGood options to account for non-21:9 format inputs via the “auto” and “1:1” modes if needed. Useful given a lot of inputs are 16:9 format.
PiP / PbPBoth supportedVarious settings and modes available
HDRNothing meaningful

VESA DisplayHDR 400 certified

FreeSync 2 certified
The screen can accept an HDR input signal but lacks any form of backlight local dimming to actually improve the dynamic range in practice. Regular Windows use looks really washed out and poor with HDR enabled.

There is a reasonable peak brightness of around 484 cd/m2, a strong wide colour gamut covering about 101.4% DCI-P3, 10-bit colour depth support and also a nice strong static contrast ratio. So from a colour point of view there are some benefits for HDR content and multimedia along with the high contrast ratio of the VA panel. It’s just not “HDR” as there’s no improvements to the dynamic range available.


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As we said when we recently reviewed the smaller 27″ GM27-CF model, it’s always nice to welcome a new manufacturer to the monitor segment, especially one who has been around the wider PC market for a long time and are well known. Cooler Master had done a nice job with their first venture and the 27″ GM27-CF offered some solid performance for gaming, and we felt that the 34″ model performed very similarly overall. The main difference here of course is the larger screen size, curved ultrawide format and larger 3440 x 1440 resolution which is a pleasure to use day to day, and gives you an attractive format for many uses. The screen is aimed at gamers and the 144Hz native refresh rate was very welcome, offering good motion clarity and high frame rate support. Like the GM27-CF, this model supports adaptive-sync for VRR from both NVIDIA and AMD systems, but also even supports variable overdrive to help control the response times – a feature normally reserved for Native hardware G-sync screens. The response times were very good for a VA panel overall, keeping up well with the high frame rates. There was some common VA black smearing due to some slower black > dark grey transitions although the level of black smearing was a little lower than many VA panels. Input lag was very low as well. The ‘MPRT’ motion blur reduction mode was unfortunately not very good though, causing too much trailing and strobe cross-talk in practice.

Away from gaming the default setup was decent enough and avoided the super-high gamma we’d seen from the smaller GM27-CF model out of the box. The Quantum Dot coating helped deliver a very wide gamut, beyond the 95% DCI-P3 spec in fact at around 101.4% coverage. This produced vivid and saturated colours for gaming which was nice, but unfortunately there was no sRGB emulation mode available for working specifically with standard gamut content. This makes it a bit limiting again for non-gaming usage for some people. The VA panel delivered solid all-round performance with the high contrast ratio and deep black depth being obvious strengths. The viewing angles were a bit weaker than other recent VA panels we’ve seen but still decent enough.

The feature set of the screen was also pretty decent, with a stable and versatile stand, integrated speakers and PiP/PbP options. On the one hand it was nice to see some additional features like this, but then on the other we missed things like USB ports (rare not to see those included nowadays) and more preset modes and gaming options from the OSD menu.

Overall we felt this was a very solid ultrawide screen from Cooler Master and if you’re looking for a 34″ VA gaming screen this is a good option to consider. It is available in some regions now from Amazon (affiliate link).

High refresh rate support and adaptive sync for VRR from NVIDIA and AMD systemsMissing an sRGB emulation mode if you wanted to work with a smaller colour space
Good response times for a VA panel overall, including variable overdrive supportMPRT mode doesn’t work very well with too much trailing and strobe cross-talk
High contrast ratio and common VA technology benefitsStill some common VA black smearing from some problem pixel response times
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