I get a little bit too excited about monitors these days, to be honest. The market for desktop PC displays has traditionally been sleepy and slow-moving, but things have changed in the past year or so. Pixel densities and display quality are up generally, and the prices for big LCD panels have been dropping at the same time. Yet in our latest TR Hardware Survey, over two thirds of our readers are rocking a main desktop monitor resolution of 1920x1200 or lower. The time has come for an awful lot of folks to consider an upgrade.
That said, perhaps the single biggest reason for PC gamers to consider upgrading their displays isn't size, pixel count, or contrast ratio. Nope, it's variable refresh technology. You may have already heard us wax poetic about the smooth animation made possible by Nvidia's G-Sync. AMD has been promising to release a competing standard under the clever name FreeSync, with the "free" implying an open standard and lower costs than Nvidia's proprietary tech. One of the first FreeSync monitors, the BenQ XL2730Z, arrived in Damage Labs not long ago, and we've been spending some quality time with it since to see how it handles.
The short answer: it's buttery smooth, just like you'd hope. Read on for our take on the current state of FreeSync, how it compares to G-Sync, and the particulars of this BenQ monitor.
Variable display refresh: the story so far
The need for variable-refresh displays stems from the fact that today's LCD monitors generally operate on principles established back in the CRT era, most notably the notion of a fixed update rate. The vast majority of electronic displays update themselves on a fixed cadence, usually 60 times per second (or 60Hz). Gaming-oriented displays are sometimes faster, but any display with a fixed refresh rate introduces a problem for gaming animation known as quantization.
Put simply, quantization introduces fixed steps into a more variable pattern of information. You've heard the effects of quantization in the autotune algorithms now used by apparently every pop singer. This same "roughness" applies visually when games produce frames at irregular intervals and display quantization maps them to fixed intervals. Here's an example from AMD illustrating what happens when a frame isn't ready for display at the end of a single refresh cycle.
With a fixed refresh rate of 60Hz, the frame-to-frame interval would be 16.7 milliseconds. If a new frame isn't ready after one of those intervals—even if it's ready in 16.8 ms—the display will show the prior frame again, and the user will have to wait until another whole interval has passed before seeing new information. Total wait time: 33.3 ms, twice what you'd usually expect—and the equivalent of 30Hz.
Now, say that GPU got really bogged down for some reason and a new frame wasn't ready for 33.5 ms. You'd have to wait three intervals, or a total of 50 ms, for the next frame to be displayed. That's a fairly punishing wait, one that would likely interrupt the illusion of animated motion in the game. Not only does it take time for the updated frame to reach the screen, but the frame that eventually gets displayed is essentially out of date by the time it reaches the user's eyes.
These 16.7-ms steps are the basis of quantization on a 60Hz display, and they unavoidably drain some of the fluidity out of real-time graphics. Quantization can make a fast GPU seem slower than it really is by exaggerating the impact of small delays in frame production. By increasing the time it takes for new frames of animation to reach the display, quantization also increases input lag, the total time between user input and a visual response.
PC gamers have often attempted to avoid the worst effects of display quantization by disabling the video card's synchronization with the display. With vertical refresh synchronization (vsync) disabled, the video card will shift to a new frame even while the display is being updated. Allowing these mid-refresh updates to happen can bring fresh information to the user's eyes sooner, but it does so at the cost of image integrity. The seams between one frame and the next can been seen onscreen, an artifact known as tearing.
Yeah, it's kind of ugly, and tearing can be downright annoying at times. Beyond that, going without vsync doesn't change the fact that the display only updates every so often.
Fortunately, today's LCD monitors don't need to follow a fixed refresh interval. Within certain limits, at least, LCDs can wait for the GPU to produce a completed new frame before updating the screen. Here's how AMD's FreeSync presentation illustrates variable refresh at work.
The display is updated right when a new frame is ready, so in the case of our example above, there's no need to wait 33.3 ms for a frame that takes 16.8 ms to render. You only wait the extra tenth of a millisecond and then paint the screen. Quantization is replaced by much smoother animation.
Obviously, variable refresh rates aren't a fix for everything. A slow GPU or CPU can still introduce frame production hiccups the user will feel. But eliminating the quantization effect does have a very nice, easily appreciable impact on a 60Hz display. I'm pleased to see this technology coming to PC gaming. It's yet another example of innovation happening in this space that will likely trickle into other markets later.
Sorting out the names and brands
Right now, unfortunately, we're faced with competing standards for variable refresh displays. You can't just buy a monitor with that feature, connect it to any graphics card, and turn on the eye candy spigot.
Nvidia was first to market with G-Sync technology, which is based on the firm's own home-brewed display logic module. Monitor makers must buy Nvidia's module in order to build a G-Sync display. Then, displays with G-Sync technology can only provide variable refresh rates when used in concert with a newer GeForce card—basically a GeForce GTX 600-series model or newer. Currently, there's a handful of decent G-Sync displays available for purchase, but they generally come with a price premium attached.
Meanwhile, AMD has taken a rather different tack with its FreeSync effort by attempting to create an industry-wide standard for variable refresh displays. The firm persuaded the VESA standards board to approve an extension to the DisplayPort spec known as Adaptive-Sync. This spec is open for the entire industry to adopt at no extra cost and is meant to ensure compatibility between GPUs and monitors capable of variable refresh rates.
Next, AMD worked with some of the biggest players in the display logic business, helping them to implement Adaptive-Sync capabilities. Three firms, Realtek, MStar, and NovaTek, have built Adaptive-Sync support into their monitor control chips—and they've apparently done so without incorporating a big chunk of DRAM like Nvidia built into its G-Sync module.
While those efforts were underway, the folks at AMD also encouraged a host of display manufacturers to build monitors with Adaptive-Sync support. Our subject today, the BenQ XL2730Z, is one of those products. As part of its FreeSync initiative, AMD has offered to certify monitors for proper variable-refresh operation at no cost to the display makers. The firm will then lend its FreeSync brand to those monitors that work properly—although FreeSync branding is by no means necessary for a display to be Adaptive-Sync compliant.
Got all that?
Thanks to its open, collaborative approach and the use of display logic chips from incumbent providers, AMD expects Adaptive-Sync support to add very little to the cost of building a display.
Of course, in order to make it work, you'll need a Radeon graphics card to pair with the monitor. Right now, only certain Radeon GPUs have the necessary hardware to support variable refresh, including Hawaii, Tonga, and Bonaire. Radeon R7 260/X, R9 285, and R9 290/X cards should be good to go, but the R9 270/X and 280/X aren't. One would hope for broader support among current cards, but AMD continues to sell some, uh, well-worn graphics chips aboard is current products.
One other caveat: multi-GPU configs aren't yet supported. AMD has pledged to release drivers that enable CrossFire multi-GPU with FreeSync some time this month.
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