Last January, we previewed how mobile G-Sync might perform on an Asus G751JY laptop that wasn’t fully certified for the feature but supported it well enough to give us a taste of what G-Sync could deliver. Today, we’re revisiting the topic, armed with a fully certified Asus G751JY-DB72. This system is nearly identical to the G751JY that we tested earlier this year, but with a handful of upgrades. Specifically, the G751JY-DB72 uses a Core i7-4720HQ CPU, 24GB of DDR3, a 256GB SSD, and a backup 1TB HDD for conventional mass storage. The system still uses a GTX 980M (4GB of RAM) and a 1,920-by-1,080, 17.3-inch screen.
At $1999 from Asus, it’s not a cheap laptop, but it’s one of the nicest and best-balanced systems I’ve ever tested. Because mobile G-Sync is a big enough feature to warrant its own treatment, we’re going to discuss the laptop’s performance and capabilities in a separate piece. For now, it’s enough to say that this is one of the best boutique laptops I’ve ever tested, even if the base model debuted a year ago.
How mobile G-Sync works
Mobile and desktop G-Sync accomplish the same goal, but they achieve it in different ways. Nvidia’s desktop G-Sync displays rely on a separate, Nvidia-built scaler unit. This scaler controls the monitor’s timing and synchronizes the display’s output with the video card. In 2013, when Nvidia debuted G-Sync, its custom scaler technology was the only way to achieve this kind of synchronization in a desktop display. That’s since changed with the launch of the VESA-backed Adaptive Sync standard (AMD calls its own implementation FreeSync). Laptops, however, don’t require custom scaler hardware — the ability to synchronize refresh rates is part of the embedded DisplayPort specification that both AMD and Nvidia use.
In order to qualify for the mobile G-Sync moniker, Nvidia requires laptop manufacturers to prove that their hardware meets certain standards. We don’t know all the details on what panels need to have, but we do know that they must support variable overdrive. Nvidia has stated that it works with ODMs to ensure that the G-Sync implementations in each laptop are tuned to the specifications of the underlying panels.
As the name implies, variable overdrive allows the display to decrease pixel ghosting by anticipating what color a pixel may need to be on the next refresh cycle and adjusting voltage accordingly. Nvidia has noted that this could result in a slight decrease in color accuracy in some conditions, but the net result should still be improved color reproduction.
G-Sync: A Goldilocks solution:
Now that we’ve covered the basics of how mobile G-Sync works, let’s talk about its specific implementation in the Asus G751JY. This laptop uses a 75Hz panel, which is important to know, because it specifies the maximum refresh speed at which G-Sync can operate. If you have a 75Hz panel and your game is kicking out a steady 200 FPS, G-Sync disables automatically and the game will switch to either V-Sync on or off. By default, NV switches to V-Sync on, since this is much less jarring then the sudden appearance of tearing, but if you prefer to disable V-Sync when the frame rate exceeds 75 FPS, you can specify that at the control panel.
This might seem less-then ideal, since gamers are typically taught to prefer high frame rates, but the relative advantage of faster FPS is subject to diminishing marginal returns. The higher the frame rate, the less visible a missed frame is.
If the frame rate falls below a certain level, however, G-Sync can run into another problem. While it doesn’t shut off due to low FPS, the GPU will automatically interpolate and insert multiple frames to smooth playback. If performance is relatively steady, this is an excellent way to smooth the game without impacting playability. If the frame rate is changing significantly from moment to moment, however, some frames will end up repeated and some will not.
PC Perspective wrote an excellent report on how FreeSync and G-Sync handle low frame rates. The graph below shows how G-Sync inserts additional frames, boosting the refresh rate as a result.
As the frame rate fluctuates, the number of frames G-Sync injects to smooth presentation can vary as well. While the end result can still be superior to not having G-Sync on at all, a variable frame rate below ~35 FPS doesn’t produce the buttery smoothness that Adaptive Sync and G-Sync provide at higher refresh rates.
This ideal window is why we call G-Sync (and Adaptive Sync) a Goldilocks solution. Both technologies work best when your frame rate is neither too high nor too low. In this case, users should target an average consistent frame rate between 40 and 60 FPS.
One of the intrinsic problems with testing a feature like G-Sync is that it’s hard to capture the output difference without a high-speed camera. One website, Blurbusters, has built a G-Sync simulator that you can use to examine the relative impact of having G-Sync enabled vs. disabled. You can see and select various display modes to compare the output, but if you choose G-Sync, be advised that the frame rate will rise until it reaches your monitor’s maximum refresh rate, then drop and start again. You can compare the output in this mode against the various other options (V-sync enabled, disabled, frame rate drops, etc).
The best video demonstration we’ve found of G-Sync vs. V-Sync On is embedded below. I’d recommend watching it full-screen and not trying to focus too hard on any one area of the image. If you relax your eyes and focus on the green line between the two rotating outputs, you’ll see that the V-Sync output on the left has a small but noticeable stutter that the G-Sync output lacks. The relevant portion of video is at 1:10.
One problem with testing a feature like G-Sync is confirmation bias. Confirmation bias is the human tendency to look for evidence that confirms a hypothesis while ignoring or discounting evidence that could disprove it. If I know that G-Sync is enabled, I may claim that a game looks better because I expect G-Sync to deliver a marked improvement. We avoided this problem by using a single-blind A/B test.
Before each test, the laptop was configured to enable or disable G-Sync. I was then asked to choose whether G-Sync had been enabled or disabled based on how the game/benchmark ran. No frame rate information or third-party tools like FRAPS, that might inadvertently hint at whether or not G-Sync was enabled, were enabled and I was not allowed to alt-tab the game or check my results until after the entire set of test runs had been concluded.
Our initial tests of BioShock Infinite failed because the game was either running well above the 75 Hz refresh rate on the Asus G751JY (and enabling V-Sync at these higher frame rates rather than using G-Sync), or running below the 30 FPS mark when we tested at 4K using Dynamic Super Resolution. We discussed the situation with Nvidia and chose IQ settings that kept the game at the 40-50 FPS mark where G-Sync’s impact is most noticeable. Once we did, I could successfully identify whether BioShock Infinite used G-Sync or not in every single test.
We also tested The Elder Scrolls: Skyrim, though in its case, we had to install additional texture mods to pull frame rates low enough for G-Sync to kick in. Again, I was able to correctly determine whether or not G-Sync was enabled in every single test. In most cases, it took just seconds — camera pans and movement are much smoother when G-Sync is enabled.
As someone who would benchmark a llama if I could find one with a PCIe slot, I’m loathe to issue an opinion that comes down to “Trust me, it’s awesome.” In this case, however, that’s what’s called for. With G-Sync enabled, camera pans are much smoother. V-Sync just doesn’t deliver an equivalent experience — not unless your game is already holding a steady 120+ FPS frame rate and you own one of the handful of monitors that support a refresh rate that high.
Is G-Sync worth it?
The FreeSync vs G-Sync battle between AMD and Nvidia has mostly played out in the desktop space, where FreeSync / Adaptive Sync displays have generally been cheaper than their G-Sync counterparts. The situation is different in mobile, where multiple vendors are shipping G-Sync-enabled laptops, while FS/AS appear to be a no-show thus far. We’ve heard rumors that this could change in the next few months, but for now, mobile G-Sync is the only show in town.
It’s true that getting G-Sync up and running properly can require some fine-tuning, but we’re not talking about anything extravagant — if you’re comfortable adjusting in-game video settings, you can tune a game to work well in G-Sync. Older titles may require some additional intervention, but if you’re comfortable installing graphics mods, it’s easy to find frame rates that showcase the feature.
Sometimes, buying into a new technology when it initially rolls out means paying a premium for a less-than ideal experience — but that doesn’t seem to be the case here. The Asus G751JY is a well-balanced system, and the GTX 980M is unmatched in mobile GPUs. True, Nvidia now offers a desktop-class GTX 980 in an ostensibly mobile form factor, but we have some significant concerns about just how that solution will actually work in the real world. The 980M, in contrast, is a proven high-performance solution.
AMD will likely counter with its own solutions — the first FreeSync demos were originally doneon a mobile platform — but for now, if you want this technology, Nvidia is the only game in town. It’s a feature that makes a significant difference, and if we were in the market for a boutique gaming laptop, we’d put G-Sync high on our list of desired features.