Do HDTV CRTs have input lag? - AVS | Home Theater Discussions And Reviews
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post #1 of 5 Old 06-02-2012, 03:04 PM - Thread Starter
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1.) Do HDTV CRTs have input lag?

2.) I heard that all HDTVs, including CRTs, use digital processing. Is there a way to completely bypass this processing to eliminate all input lag?

3.) Do HDTV CRTs have native resolutions?

Thanks
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post #2 of 5 Old 06-03-2012, 08:01 PM
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Quote:
Originally Posted by GeneraLight View Post

1.) Do HDTV CRTs have input lag?

What is commonly called "input lag" probably should be called "display lag", since the delay (in question) is introduced after the input port of the TV and prior to display. The (total) delay/lag you encounter when you enter input on a game controller and see the results on screen is partly due to the response time of the game console, where the term "input lag" would be more appropriate.

In comparing a common signal to a Sony 30XBR910 (the CRT HDTV) versus a Sony 27XBR15 (from 1989), I was able to measure a difference between the two TVs. The image capture was low-resolution and at only at 15 frames per second, but I compared a moving object relative to a stationary object on each screen, with the two TVs side-by-side. The image on the HDTV seems to be delayed by about one frame time as compared to the SDTV. The frame time and the delay time being similar (about 67 milliseconds) is probably a coincidence.

I'll leave it to the reader to make any generalization at their own risk.

Quote:
2.) I heard that all HDTVs, including CRTs, use digital processing. Is there a way to completely bypass this processing to eliminate all input lag?

Probably not.
But it might be interesting to test/measure a TV such as the 4:3 Sony HighScan models (e.g. 3xHS510) that display 4:3 SD content full screen, but 16:9 content is "letterboxed" by compressing the 1080 interlaced raster lines. Perhaps the SD content has minimal processing (hence minimal delay) since the image is not being upscaled (to 1080i like on the XBR910).

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3.) Do HDTV CRTs have native resolutions?

Monochrome CRTs (e.g. "black & white" TVs and 3-tube CRT projectors) do not have a "native resolution". A monochrome CRT has a clear path between the electron gun and phosphor screen, so the number of pixels that can be displayed is essentially limited by the bandwidth of the electronics & tube(s), beam size and the phosphor grain.

A color CRT has a screen composed of a mix of red, green and blue phosphors, arranged in dot trios or stripes. A shadow mask or aperture grille is positioned between the electron guns and the phosphor surface so that each gun will only activate its matching color (e.g. the electron gun for "blue" can only strike the blue phosphors and is blocked from the red & green phosphors). The resolution of the input video does not have to exactly match the display (like a fixed-pixel display) or else be scaled to do so, as long as the electron guns can turn on & off within their bandwidth. But there is an optimal resolution since there are discrete pixels visible on the color CRT's face. Ideally the resolution of the signal matches one-for-one the "native resolution" of the tube, as dictated by its dot pitch. If the signal resolution does not match up to the dot pitch, then more or less (phosphor) dots are or are not lit up. Each gun (for each color) just turns on and off per the input signal, and there's no harm or foul if the beam is on for more than one (phosphor) dot (or less than one dot). (Fixed-pixel displays do not have it simple; each pixel has to be individually addressed and controlled, hence the input resolution has to be scaled to exactly match the panel.) Some CRT HDTVs, such as the xxXBR910, upscale all input to 1080i with excellent results in order to reduce visible scan lines of standard NTSC displays.
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post #3 of 5 Old 06-03-2012, 08:34 PM
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In general most HD CRTs upscale inputs to 1080i. They also usually display 480p or 540p but may be limited to doing so only when fed a 480p signal via component or HDMI (which is how my Toshiba set does it). Lag is probably slightly more than a SD Tube but I've successfully played many old fast 2D games from the NES and SNES era on my Toshiba HD CRT without issues. I was able to beat Double Dragon 3 on the HD CRT and I hadn't done that since years earlier playing it on a SD CRT set (using the actual NES system outputting 240p which is then scaled to 1080i). I set my Wii to output 480p and the TV to display it at 540p as I feel that this will be less overall scaling of the signal than allowing upscaling to 1080i. I've been very successful at playing Goldeneye Wii online with the HD CRT set, so any lag is very minimal and I can't say I notice any lag like I might on an LCD set.
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post #4 of 5 Old 06-06-2012, 05:46 AM
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Quote:
Originally Posted by GeneraLight View Post

2.) I heard that all HDTVs, including CRTs, use digital processing. Is there a way to completely bypass this processing to eliminate all input lag?

Yes there is, sort of.

I own a Sony XBR960, and I managed to enter the service menu and disable HDPT ( high definition pass through ), which eliminates all input lag when the television is outputting at 1080i. It seems like there is zero input lag in comparison to the tiny bit I was getting when HDPT was turned on. This fast response time is very noticeable when playing PS3 games in 1080i ( though, it's a shame so few games support this resolution ).

I'm not aware of a way to do this for 720p signals. Disabling HDPT only works for 1080i on mine.
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post #5 of 5 Old 06-06-2012, 08:02 AM
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Might see if the TV has a game mode selection in the user menu. My Panasonic Tau does, it displays normal content with fine horizontal lines but other than that I don't know what it does in terms of gaming.

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