Nvidia
The big news from Nvidia might be the release of the GTX 980 Ti, but the company has also announced some updates to G-Sync. Variable refresh rate technology, which synchronizes a compatible monitor’s refresh rate with a game’s frame rate, is finally making the leap from desktop to laptop. Upcoming laptops from Gigabyte, MSI, Asus and Clevo are all set to support the technology and will feature 75Hz panels from 1080p to UHD (4K).
Desktop users aren’t forgotten either: there are some new monitors, including a lust-worthy 34-inch 21:9 75Hz IPS Acer X34 panel, with an updated G-Sync module that finally includes more than just a single DisplayPort input.
Interestingly, G-Sync for laptops uses the built-in DisplayPort (eDP) standard, a standardized interface for connecting display panels directly to internal graphics cards. On the desktop, G-Sync can only be used with compatible monitors that include Nvidia’s G-Sync module.
According to Nvidia, the reason desktop displays need a G-Sync module is that it provides a much more manageable end-to-end solution for consistent performance. However, there is no module for G-Sync laptops. Instead, the display is controlled directly by the GPU, which does double duty as both a scaler and a graphics card. G-Sync takes advantage of this connection and the panel’s variable timing and self-refresh functionality built into eDP, effectively implementing G-Sync in software.
The more technically minded will notice that this is so terribly similar to how AMD’s FreeSync works on the desktop, the technology being based on DisplayPort Adaptive-Sync, which in turn was based on eDP.
While the underlying technology differs, Nvidia claims that G-Sync can control laptop screens in exactly the same way as desktops, except by using standardized eDP functions instead of proprietary hardware. The end result should be the same: smooth gameplay without the input lag and jitters of v-sync, or the screen tearing that occurs when v-sync is off.
Nvidia
Although G-Sync on laptops is based on an open standard, not every laptop will support the G-Sync compatible name. Of course, the laptop needs an Nvidia GPU, but more importantly, the screen needs to be connected directly to that Nvidia GPU. Nvidia’s Optimus graphics solution, which allows the laptop to switch between an integrated GPU and the discrete GPU to save power, is not currently compatible with G-Sync. Nvidia is also implementing a qualification process for all manufacturers that want to use the G-Sync brand, where individual components go through an optimization process that looks at refresh properties and pixel response times to set the correct G-Sync timings.
But why does my desktop monitor need a G-Sync module…
The question is, if Nvidia can implement G-Sync on laptops using the open eDP standard, why can’t it do the same with G-Sync on the desktop? It’s an important question, as the company has decided to reveal some of the secret sauce behind G-Sync, especially when compared to FreeSync, and that everything will work on laptops.
While FreeSync received a positive reception, many reviewers (myself included) noted that there was some ghosting that wasn’t present in G-Sync, as well as flickering issues at lower frame rates. The folks at PC Perspective did an analysis of G-Sync and FreeSync a while back, looking at what happens at lower refresh rates, and it turned out that their findings are pretty much the same regarding the underlying technical differences between G-Sync and FreeSync. FreeSync.
Nvidia has confirmed that the desktop versions of G-Sync and the upcoming laptop version use variable overdrive. The technology adjusts the amount of overdrive applied to a pixel – that is, driving pixels faster to ensure they reach the desired color faster – to make them compatible with variable refresh times. Overdrive was originally designed with a fixed refresh rate in mind. The screen knows that if it pushes a pixel harder at just the right time, when the next refresh rolls around that pixel, that pixel will gradually and in time fade back to the desired color, increasing the perceived response time.
Nvidia
Unfortunately, the variable response technology monitor no longer knows exactly when the next refresh window will be. In this situation, if overdrive continues to operate in the same way, the pixels will not match the timing of the data coming from the graphics card, causing visible ghosting. According to Nvidia, this is what happens with FreeSync, and G-Sync’s variable overdrive technology fixes it. Variable overdrive tries to predict when the next frame will arrive and adjusts the timing of the overdrive to compensate. While this system will never be 100 percent accurate, reducing color accuracy, it does help reduce ghosting, as evidenced by how well G-Sync works on the desktop.
In addition to variable overdrive, Nvidia also confirmed at a recent event what happens in a situation where a game’s frame rate drops below the monitor’s minimum refresh rate. Instead of reverting to v-sync on or off as FreeSync currently does, complete with its associated issues, G-Sync inserts duplicate frames instead. So, for example, while your system is pushing a frame rate of 25 FPS, the G-Sync monitor actually doubles this to 50 FPS, returning the game to the variable refresh rate window.
Despite Nvidia’s gentle prodding of AMD’s FreeSync technology, the company picked up a feature from its rival. G-Sync users now have the option to enable or disable v-sync when a game’s frame rate exceeds a monitor’s maximum refresh rate. While this isn’t as common if you’re using a 144Hz TN panel, those with IPS panels that top out at 75Hz may find the option useful. G-Sync also now works with games that run in a window, which can be useful for those planning a sneaky bit Dota 2 in the office, but won’t settle for the shaky weaknesses of v-sync.
List image by Nvidia