Eli5 : what is vrr ‘ variable refresh rate’ and why is it useful?
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There’s a whole Wikipedia article on it.
Basically, before displays were only fixed frame rates, say 30Hz. For a 60Hz display, it would just double the 30Hz, but it couldn’t properly play 45Hz.
Modern video games can be rendered basically at whatever the max the computer can handle. More intensive scenes lower the frame rate. A variable refresh rate is what it sounds like, it varies the refresh rate so that the computer isn’t trying to refresh when the frames haven’t been loaded yet, so it drops down from say 120Hz to 100Hz.
Computer monitors traditionally run at a constant refresh rate. That is, the image coming from the PC/graphics card is sent at a consistent rate over the cable. 60 Hz is most common. Even if the image isn’t changing, a new copy is sent 60 times a second regardless, with even spacing between frames. But for smoother experiences, higher refresh rates like 120 Hz are preferable, maybe even higher. A gaming monitor almost certainly does 120 Hz, and we’ll assume it can and that it does.
Note that the image is being sent over the cable over time. You can’t send a whole image instantly. It takes a few milliseconds. At 120 Hz, one frame is about 8.3 milliseconds, so the image has to be sent within that amount of time. Higher refresh rates will reduce the number of milliseconds.
However, video games require a varying amount of time to prepare an image. The CPU and GPU are doing a lot of work. If the next image isn’t ready before the graphics card starts re-sending the old frame then, you have two options: wait for the current frame to finish being sent to the monitor and then have this one sent, or splice the frame in, resulting in the monitor drawing half the old image (top half) and half the new image (bottom half). This effect is called “tearing”, since you can see a seam on screen where the two images got spliced in. Waiting for the monitor to be ready is often called the “vsync” option in video game graphics settings.
“Vsync” is the game waiting on the monitor to be ready. But Variable Refresh Rate is the other way around: the monitor waits for the game. The graphics card stops sending frames to the monitor and it just holds the current image on screen. When the frame is ready, the graphics card resumes transmission, and the next frame shows up whenever that is. There’s still a maximum rate – 120 Hz in our little example. But the amount of time between frames is no longer locked at 8.3 milliseconds, being allowed to be whatever it needs to for the game to draw the next frame. No more tearing, and no delivery delays.
On a smartphone, VRR is used to save battery. So, let’s assume you’ve got yourself a brand new phone with a screen capable of a refresh rate of 120Hz. That means, the screen refreshes itself 120 times per second, even if it’s just displaying the default static wallpaper of the homescreen, which leads to higher battery drainage.
With VRR, the phone can detect if the image is still, and decrease the refresh rate to, say, 1Hz. Then, as soon as you the image moves, it increases again to 120Hz. Therefore, you are saving tons of battery.
It also works with content, of course. If you’re watching a 60fps YouTube video, then the refresh rate will cap at 60Hz while you’re watching, and so on. This goes more along the lines of what other comments have already explained.
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