What a fixed refresh gets wrong
A fixed refresh screen shows a new image at evenly spaced moments. If a frame isn't ready in time, the screen has two bad options. It can keep the old frame up, which looks like judder. Or it can switch to the new frame partway through, so one refresh shows a mix of old and new, which is tearing.
Here's the judder case. A game running at 50 fps finishes a frame every 20.00 ms. A 60 Hz screen with V-Sync refreshes every 16.67 ms. Most frames show for one refresh, but now and then a frame has to stay up for two, 33.3 ms in all. That uneven beat is the stutter you feel. With VRR the screen refreshes when the frame arrives, so every frame stays up for 20.00 ms.
The range and what happens outside it
A VRR display only follows the game inside a band of refresh rates, like 30 to 144 Hz. Inside the band, the refresh matches the frame rate. Outside it, something has to give.
Below the band, many monitors use low framerate compensation. They repeat each frame to stay in range. A game at 25 fps makes a frame every 40.00 ms, and showing each one twice makes the screen refresh every 20.00 ms. Above the band, the screen can't follow, so you're back to tearing or V-Sync waiting. On a G-Sync display with V-Sync on, NVIDIA's latency guide says Reflex or Ultra Low Latency Mode caps the frame rate below the refresh rate, which keeps a game inside the range.
Which name is which
The names overlap, and all of them do the same job. Here's how they relate:
- Adaptive-Sync is VESA's version, an optional DisplayPort feature formally introduced with DisplayPort 1.2a in 2014
- FreeSync is AMD's version, royalty free and also available over HDMI. FreeSync Premium requires low framerate compensation and at least 120 Hz at FHD, and Premium Pro adds brightness and wide color gamut requirements
- G-Sync is Nvidia's proprietary version. The original needs a G-Sync module in the monitor in place of the usual scaler
- G-Sync Compatible is Nvidia's label for FreeSync monitors it has tested. They turn G-Sync on automatically with a GeForce card from the GTX 10 series on
- HDMI VRR is the version built into HDMI 2.1
So the question isn't which brand is better. It's whether your graphics card, monitor and cable all speak the same version.
What VRR doesn't fix
VRR doesn't make a slow graphics card faster. At 40 fps the frames are still 25.00 ms apart, and they just arrive evenly.
Pixel overdrive also gets harder to tune when the refresh rate keeps changing. A setting that looks clean at a monitor's top refresh rate can look different lower down. The overdrive comparison guide shows how to check.