Subject: Graphics Cards | April 16, 2013 - 03:01 PM | Ryan Shrout
Tagged: vsync, stutter, smoothness, microstutter, frame rating, animation
We are running a poll in conjunction with our Frame Rating: Visual Effects of Vsync on Gaming Animation story that compares animation smoothness between fixed 30 FPS and 60 FPS captures and Vsync enabled versions.
If you haven't read the story linked above, these questions won't make any sense to you so please go read it and then stop back here to answer the polls!
Not a simple answer
After publishing the Frame Rating Part 3 story, I started to see quite a bit of feedback from readers and other enthusiasts with many requests for information about Vsync and how it might affect the results we are seeing here. Vertical Sync is the fix for screen tearing, a common artifact seen in gaming (and other mediums) when the frame rendering rate doesn’t match the display’s refresh rate. Enabling Vsync will force the rendering engine to only display and switch frames in the buffer to match the vertical refresh rate of the monitor or a divisor of it. So a 60 Hz monitor could only display frames at 16ms (60 FPS), 33ms (30 FPS), 50ms (20 FPS), and so on.
Many early readers hypothesized that simply enabling Vsync would fix the stutter and runt issues that Frame Rating was bringing to light. In fact, AMD was a proponent of this fix, as many conversations we have had with the GPU giant trailed into the direction of Vsync as answer to their multi-GPU issues.
In our continuing research on graphics performance, part of our Frame Rating story line, I recently spent many hours playing games on different hardware configurations and different levels of Vertical Sync. After this time testing, I am comfortable in saying that I do not think that simply enabling Vsync on platforms that exhibit a large number of runt frames fixes the issue. It may prevent runts, but it does not actually produce a completely smooth animation.
To be 100% clear - the issues with Vsync and animation smoothness are not limited to AMD graphics cards or even multi-GPU configurations. The situations we are demonstrating here present themselves equally on AMD and NVIDIA platforms and with single or dual card configurations, as long as all other parameters are met. Our goal today is only to compare a typical Vsync situation from either vendor to a reference result at 60 FPS and at 30 FPS; not to compare AMD against NVIDIA!!
In our initial research with Frame Rating, I presented this graph on the page discussing Vsync. At the time, I left this note with the image:
The single card and SLI configurations without Vsync disabled look just like they did on previous pages but the graph for GTX 680 SLI with Vsync on is very different. Frame times are only switching back and forth between 16 ms and 33 ms, 60 and 30 instantaneous FPS due to the restrictions of Vsync. What might not be obvious at first is that the constant shifting back and forth between these two rates (two refresh cycles with one frame, one refresh cycle with one frame) can actually cause more stuttering and animation inconsistencies than would otherwise appear.
Even though I had tested this out and could literally SEE that animation inconsistency I didn't yet have a way to try and demonstrate it to our readers, but today I think we do.
The plan for today's article is going to be simple. I am going to present a set of three videos to you that show side by side runs from different configuration options and tell you what I think we are seeing in each result. Then on another page, I'm going to show you three more videos and see if you can pinpoint the problems on your own.