When we pinpointed multi-GPU micro-stuttering in our recent article, we mentioned a couple of things about it that would require further investigation, including perhaps the use of high-speed cameras in order to capture the effects of micro-stuttering (and, hopefully, of Nvidia's frame metering technology designed to combat those effects.)
The response to the article has been overwhelming, and I want to thank everybody who took the time to send a note or post a comment. As I've been sifting through the feedback, I've already learned some things. One of the best bits of info on the subject comes courtesy of Carsten Spille of GPU-tech.org, who had already managed to capture the effects of micro-stuttering quite nicely on video. Have a look:
Very educational. I take several lessons from this video. One, it validates my argument that the high-latency frames in a jitter pattern can be the gating factor for the perceived illusion of motion. Although the multi-GPU setup produces a Fraps readout of 60 FPS, it looks no smoother than the single-GPU setup at 30 FPS, and multi-GPU at 30 FPS doesn't look as smooth as the single GPU at the same rate. This case may be an extreme one, but the effect of those high-latency frames is clear.
I'll pause here to reiterate an important point. I said in the article that I'd never been able to detect multi-GPU micro-stuttering myself, and some folks seem to have taken that statement to mean that micro-stuttering doesn't have any real impact on the user experience. But I was talking about a specific aspect of the problem: the visual disruption caused by uneven frame delivery. Even if you can't "see" jitter—that is, if you can't easily perceive the long-short-long-short pattern of uneven frame delivery with the naked eye—pretty much anyone should be able to notice the reduced fluidity caused by the longer latencies in every other frame (once frame times grow high enough.) Nvidia's frame metering has the potential to reduce or largely eliminate the perception of long frame times, at least with certain game engines. Without metering, though, their impact should be easily perceptible, just as it is in the video.
With that said, the high-speed capture does seem to show us a second, "runt" frame that comes just after a major screen update. So even if you can't see the visual distrubance with the naked eye, the effect is there on video, slowed down for all to see.
Also useful is the in-game setting for this video and the content of the frames, which seems well suited to showing the effects of micro-stuttering. The side-to-side motion appears to help tease them out, too. I'm off to IDF this week, so I can't do any further experimenting for a few days, but I'll try a little strafing in high-contrast areas when I return. If you're looking for micro-stuttering in your own setup, you might want to try the same.
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