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Micro-Stuttering: So Subtle, Yet So Annoying

Micro-Stuttering And GPU Scaling In CrossFire And SLI
By , Greg Ryder

What Is Micro-Stuttering?

Let’s recap how successive frames are generated. Since the ideal "perfect balance" isn't achievable in the real world and the system cannot render, say, 30 frames in advance, the following scenario is typical:

What we have here is a close-up of one second of Metro 2033 game play, rendered on a pair of Radeon HD 6850 GPUs. We chose this title and hardware combination because it yields a frame rate very close to 30 FPS. That's where the micro-stuttering phenomenon, if it exists at all, is rumored to be most aggravating.

Looking at the diagram, we immediately spot the dramatic variation in the number of milliseconds it takes to render each frame. The pie chart shows all 30 frames within the one-second period that we analyzed. It's easy to notice the delay of some frames, which is, in turn, perceived as stuttering. And of course it doesn’t help when the next frame catches up to help keep the average frame rate high enough.

You end up with what feels like a stuttering engine. Yes, it's going 30 MPH just like a smooth inline-six. But this one hits the same speed and feels like it has one cylinder out of whack. .

When Can Micro-Stuttering Be Seen?

In a nutshell, all of the time. The lower the average frame rate, the more the frame rate is perceived as being lower than the actual average frame rate. Thus, as bad luck would have it, a frame rate of 30 FPS may be perceived as merely 20 to 25 FPS. The human eye does, however, still notice differences in when frames show up on-screen beyond 60 FPS.

This is one of the reasons why we prefer testing with higher frame rates in the GPU scaling tests on the following pages. It continues to amaze us how, even beyond the generally-accepted target of 40 FPS, you can still see the impact of micro-stuttering once rendering becomes imbalanced.

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