General tech inquiry - Active shutter frame synchronization w/variable framerate - AVS Forum
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post #1 of 4 Old 07-05-2012, 04:37 PM - Thread Starter
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I've just been thinking about this, and wondering if anyone could shed some light. This is more or less aimed at 3D gaming scenarios rather than fixed-framerate sources like movies or TV.

In gaming, especially with PC gaming, you can get a variable framerate from one moment to the next. Now it's 60fps, now it's 57fps, now it's 62fps, now it's down to 34fps, back up to 46fps, etc. Seems worse when playing in 3D since it's effectively having to render everything twice, which causes a general hit to framerate most of the time.

My question is: How do active-shutter glasses compensate for this, and how effectively do they do it? I know there's live communication going on.. the glasses are being told when to open and close, which eye at what frequency, etc. But how effective is it at keeping up when the framerate changes? I'm sure the glasses can adjust their shutter speed on the fly, but is there lag involved, allowing some crosstalk through for a frame or two? Is it noticeable to the player?

I'm just curious, in how the hardware handles it at a technical level. Thanks. smile.gif

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post #2 of 4 Old 07-05-2012, 07:02 PM
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The more demanding the game software, the less the number of new frames the pc can create per second and send as updates to the display buffer.

This doesn't affect the screen refresh rate for the display. For 3D this will typically be at 120Hz. It will remain at 120Hz even if the frame buffer is, for a short period only being updated at say, to use your example, 34fps.

The screen repeats the same Left and Right images until the frame buffer receives its next update. The shutter glasses continue to operate at 120Hz. Cheers.
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post #3 of 4 Old 07-05-2012, 08:30 PM - Thread Starter
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Hm.. so I'm overthinking it.. lol. I was under the impression (for whatever reason) that the shutter speed of the glasses would have to match the effective framerate of the content being displayed.

Good enough. Thanks. smile.gif

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post #4 of 4 Old 07-06-2012, 02:44 PM
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The display processes and places the incoming content in a software controlled buffer at the speed at which it is received or processed to. The display is then actually updated to create a new image by taking the content of the software buffer at the displays native refresh rate. A simple example is 24fps content left in the software buffer for 1/5th of a second will be displayed 5 times since 5x24=120 on an 120Hz LCD unit.
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