Answers and Thoughts
Well, did you write down your answers? Here is the key.
60 FPS vs 30 FPS comparison
- 60 FPS is on the left, 30 FPS on the right
60 FPS vs Vsync
- 60 FPS is on the left, Vsync is on the right
30 FPS vs Vsync
- Vsync is on the left, 30 FPS is on the right
How did you do? I think most users will be able to get the first two comparison without much work and only the third one that compares a static 30 FPS animation and a variable frame rate animation will be difficult.
What does this really mean based on our previous Frame Rating data sets, AMD's CrossFire issues and user experiences? First, not everyone can tell the difference between the videos we have created here and even some that can will prefer the Vsync options over the 30 FPS reference video we created. Because of that, there is no single fixed answer to the problems we are working on. At least not yet.
Some reps from AMD told me at a meeting during GDC that there were no animation issues once you enabled Vsync and that the constant shift from 16 ms to 33 ms times were imperceptible. I think our videos here have quite definitely discounted that theory. There can still be a debate of how much that difference affects gamers, but there shouldn't be any more debate on if it exists.
And of course, enabling Vsync results in a situation where the frame rate does NOT dip below 60 FPS, as we did with our reference videos used in this article, will not result in animation inconsistencies. Gamers, gaming PCs and game settings that result in a frame rate under 60 Hz will see frame rate bouncing like we are seeing in our Battlefield 3 and Sleeping Dogs demonstrations today. In those cases, the debate about the value of Vertical Sync will continue.
I am staunch believer that a smooth animation is just as important as the frame rate of said animation, and that is why I have invested so much time and money in the idea of capture-based performance testing and the Frame Rating articles up to this point. We have created a great discussion amongst gamers and enthusiasts alike, many of whom where not aware that problems like this even existed.
Other Vsync Considerations
The second big concern after animation consistency when enabling Vsync is the problem of input latency. Input latency is the time between an input being given by the user (mouse movement, click, keyboard press) and when the result of that action actually displays on the screen. There are lots of factors that come into play here including the game engine time, the rendering time and display time. With Vsync enabled on your game you are often forcing the result of your actions to "wait" to be displayed by a complete frame time, 16 ms.
Image source: Anandtech
Many articles have been written about testing input latency (input lag sometimes) over the years and this one from Derek Wilson at Anandtech comes to mind as being a solid explanation. The effect of Vsync on input latency will vary from game to game, but in many cases the addition of Vsync adds at least 1 full frame or latency to the configuration.
It is for that reason that we many gamers choose to play PC titles without Vsync enabled – regardless of their stance on the horizontal tearing seen without it.
We are working on another way to test input latency in a more scientific way, hopefully by utilizing portions of the Frame Rating system we have created. Intercepting specific mouse and keyboard DirectInput commands while also measuring frame placements seems like it could offer a compelling and reliable way to measure input delays. More on that soon!
Today's article was meant to address the theories revolving around Vertical Sync and animation smoothness, and I think with our videos and descriptions most users will be able to see how experiences are affected. 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!! But keep in mind that we are engaging in a discussion, not telling you how you should feel! Let me know in the comments, or in an email, what you think about the results we showed and if you agree or disagree with our statements on the experiences they provide!