AMD Radeon HD 7990: Eight Games And A Beastly Card For $1,000

Test Setup, An Explanation Of FCAT, And Benchmarks

Our work with Nvidia’s Frame Capture Analysis Tools last month yielded interesting information, and it continues to shape the way we plan to test multi-GPU configurations moving forward. Because it’s such a departure from the Fraps-based benchmarking we’ve done in the past, though, today’s review includes more than just FCAT-generated data. We’re also bringing a handful of gamers to our SoCal lab to go hands-on with Radeon HD 7990 and GeForce GTX 690 in eight different titles. What we’re hoping to achieve is unprecedentedly comprehensive performance data using FCAT, and then the real-world “reality check” from gaming enthusiasts. We want to know if this new emphasis on latency between successive frames maps to the actual gaming experience.

At the same time, we recognize that the new data we’re generating is far more sophisticated than the simple average frame rates that previously made it easy to pit two graphics cards against each other. Fortunately, we still have average results to report, along with frame rates over time. The newest addition is frame time variance. We’ve heard that this isn’t as explanatory as we’d hoped, so we have the following explanation to help clarify.

Why aren’t we simply presenting frame times, as other sites are? Because we feel that raw frame time data includes too many variables for us to draw the right conclusions.

For example, a 40-millisecond frame sounds pretty severe. Is this indicative of stuttery playback? It might, and it might not. Take the following two scenarios:

First, how would your game look if that 40-ms frame was surrounded on both sides by other frames that took the same amount of time to render? The resulting frame rate would be a very consistent 25 FPS, and you might not notice any stuttering at all. We wouldn’t call that frame rate ideal, but the even pacing would certainly help experientially.

Then consider the same 40-ms frame in a sea of 16.7-ms frames. In this case, the longer frame time would take more than twice as long as the frames before and after it, likely standing out as a stutter artifact of some sort.

Yes, the hypothetical is simplified for our purposes. But the point remains; if you want to call out stuttering in a game, you need more context than raw frame times. You also need to consider the frames around those seemingly-higher ones. So, we came up with something called frame time variance.

We’re basically looking at each frame and coming to a conclusion whether it’s out of sync with the field of frames before and after it. In the first example, our 40-ms frame surrounded by other 40-ms frames would register a frame time variance of zero. In our second example, the 40-ms frame surrounded by 16.7-ms frames would be reported as a variance of 23.3 ms.

Experimentation with this in the lab continues. But from what we’ve seen, gamers are noticing changes as small as 15 ms. Therefore, this is our baseline. If frame time variance is under 15 ms, a single frame probably won’t cause a perceptible artifact. If the average variance approaches 15 ms, with spikes in excess, it’d be reasonable to expect a gamer to report stuttering issues.

The actual Excel formula we’re using on frame times listed chronologically from top to bottom is as follows:

=ABS(B20-(TRIMMEAN(B2:B38, 0.3)))     //The formula describes the frame time variance for the 20^th frame in a capture, listed in cell B20.

Breaking this down, the formula looks at frame time values starting 18 cells in front of and 18 cells behind the targeted frame, and then averages them out (excluding 30% of the outliers so that the average isn’t affected by anomalous results). This average frame time is then subtracted from the current frame time. The result is fed back as an absolute, or positive value.

We’re always hoping to see frame time variance of zero. In reality, though, there is always some variation one way or the other. So, we look across the spectrum and report average, 75^th, and 95^th percentile values.

I know—sounds like it gets pretty intense. But you’re going to see some pretty cool details from the nearly 1.5 TB of video we captured from AMD’s Radeon HD 7990, two Radeon HD 7970s in CrossFire, the Nvidia GeForce GTX 690, GeForce GTX Titan, and two GeForce GTX 680s in SLI. All of the testing was done at 2560x1440, and we’re using eight different games to represent each solution’s performance.