Digital Foundry vs. Console Lag: Round Two

PlayStation 3 and Arc camera put to the test.

It's been a week where Microsoft's PR efforts in promoting Natal to the mainstream press and celebs alike have been met with mixed fortunes. While Peter Molyneux soldiers on with good work evangelising the tech to both consumer and specialist press alike, puzzlingly the hands-on demos continue to run on the aged E3 2009 platform. Nobody outside selected, NDA-respecting developers knows the quality of the production version.

However, the potential is obvious: no less a man than Jonathan Ross describes it as "impressive... sky's the limit" but at the same time cautions that it's "not quite there yet", while his son went so far as put a disclaimer about the lag on his YouTube video showing Dad in "action". Hey, Natal news is so thin on the ground that we'll take it where we get it.

The truth is that Xbox 360 games in general and Natal in particular have been fairly easy to measure for so-called controller lag: the time taken between human movement and the action occurring on-screen. We've got a Ben Heck controller board for measuring 360 response while the video demo of Natal in our hands-on at gamescom last year speaks for itself and was the first real effort to measure its responsiveness.

So, can PlayStation 3 and its so-called "Arc" motion controller offering be put to the test in any kind of meaningful way? So far, the project has been even more carefully guarded than Natal. Less than two weeks from now, GDC kicks off and with it the first opportunity to get a good look at the wand and hopefully go hands-on with the motion controller. I expect it to be very good: after all, most of the component technologies that comprise the system are out there now for anybody to try.

The wand itself hooks up to the PlayStation via Bluetooth - just like your SixAxis or Dual Shock 3 - while motion-tracking of the wand itself is achieved using the PlayStation Eye, another piece of tech freely available to anyone. I picked up mine from the online SonyStyle store over Christmas for £15.

That being the case, we can assume that button presses on the wand will be as instantaneous as they would be on the traditional controller, while the accelerometer and inertia sensors would transmit in the same way, at the same speed. Movement is tracked using an already-available PS3 peripheral: the PlayStation Eye has plenty of software out there that already judges motion and processes video. This very nice little piece of tech has been pulled apart and reverse-engineered to the point where PC drivers are available courtesy of enterprising coder "AlexP". He confirms Sony's spec of 640x480 imaging at up to 60FPS, while the lower-resolution 320x240 mode is capable of double that.

Crucially for the purposes of our discussion, he is able to measure the camera's latency at just one frame, or 16.67ms. For the Arc project, Sony could’ve binned off the camera and used a new one, but PlayStation Eye's impressive spec is accomplished enough that they didn't need to do so.

But how does that one frame latency translate into actual gameplay?

Motion detection works by having the PlayStation Eye track the glowing, bulbous tip of the Arc wand and while we can expect plenty of tooling around and optimisations of the core libraries at Sony HQ, we can still get a good idea of how processing motion and video works in the here and now.

Sony's bundled PlayStation Eye tool, EyeCreate, can be used to give a best possible processing scenario. Boot it up and you'll see that it displays PlayStation Eye's input as is, with full resolution 640x480 at 60 frames per second. In these "best case" conditions, latency is slight - ballpark with 60FPS gaming titles like Burnout Paradise. PSN title Mesmerise is another interesting test: it processes the camera input for any changes whatsoever and turns those changes into a 3D visual. It's not Arc but both show the same underlying tech in use on the only area of the peripheral likely to incur game lag.

PSN title Mesmerise in action. Its cute visualiser using PlayStation Eye. Display lag on this Dell monitor has been measured at 50ms, so that has to be factored out when evaluating the video.

Results are intriguing. Mesmerise - a 60FPS title - appears to lag behind human motion by between 100 and 133ms. A more exact measurement isn't really possible. That figure takes into account the fact that the monitor involved scales slowly (720p has a three-frame, 50ms latency) and was used simply because it has been calibrated. We know how slow it is, making our measurement more accurate. I expect Arc to be the same, or better, in similar gaming circumstances.

Analogues for those figures can be found by measuring actual gameplay and we go to GDC expectant that Arc will work well as a direct joypad replacement. There's zero reason whatsoever to expect that button presses will be any less responsive than the trusty Dual Shock 3, and while movement might feel a touch less responsive, wand motion should carry far more information in terms of movement/trajectory. To put it basically, pointing is more accurate, precise and natural. As a parallel, the Wiimote has more lag than the PS3 pad, but there's no doubt that you can point and shoot at opponents far more quickly in the Wii rendition of Call of Duty 4, for example.

It's worth remembering of course that even factoring out the controller, game lag can vary massively from title to title. Now, for the first time, the PS3 can be put through its paces in controlled conditions. Digital Foundry has had a go at this before, of course. Back in September last year, we took a good, hard look at the latencies built into console gaming, with the emphasis on Xbox 360 titles.

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