LCD refresh rate issue

[corkyg]

Originally posted by: FifthElement
I have to strongly disagree with refresh rate not being important for LCD panels. The reason for this is simple: In order to avoid image tearing, you must enable vertical sync. But if you do that, you limit yourself to the refresh rate. So, the higher your "synced" refresh, the higher your FPS.
On my ViewSonic VX922, I use 75Hz when gaming (The max I can). 60Hz synced is far to slow for my taste. If you can game without v-sync, then the issue is irrelevant. But the tearing issue is just too distracting for me, thus in my case, the higher refresh, the better.

That is incorrect. You just don't understand how LCDs work. They do not have vertical synchronization - nor tearing due to that.

While your observations of an effect may be correct, your conclusions as to their cause are not.

LCD

It really makes no difference at all what you set your ViewSonics refresh rate at - it will always perform the same because it does not refresh at all. Each pixel has a response time, and only newer LCDs are suitable for gaming because of that.

 

[xtknight]

It's a very complicated matter. The DVI connection itself can appear to transmit a refresh rate higher than 60 Hz and the monitor OSD measures that for vertical frequency and pixel clock. It may very well end up to be 75 Hz or 85 Hz on the lower resolutions. The TFT panel itself as driven by monitor electronics cannot receive an update rate of higher than 60 Hz (the DSP interpolates to achieve the smoothest 60 Hz motion from the 75 Hz signal and sends it to the TFT). Saying they don't refresh is misleading, because the monitor itself very well has to receive a vertical blanking signal to operate correctly. A couple LCDs (only the Samsung 970P comes to mind at this point) have trouble keeping their response time down with the higher refresh rates, due to the overdrive chip lacking a "look up table" for that refresh rate.

What I certainly know for sure is that, even with the interpolation, the 75 Hz refresh rate (as selected in Windows and reported in the OSD) on an LCD feels a lot smoother (just move your mouse), much like a CRT. Just make sure your overdrive is still working properly. Syncing to VBlank on an LCD should result in a much smoother image as well.

 

[corkyg]

Originally posted by: Talcite
isn't the refresh rate the rate at which frames are sent to the LCD? hence, the higher the refresh rate, the better? and yes I've heard the argument about how you can't see over 30fps or whatever, i just don't buy it.

No! Refresh rate is the rate at which a CRT rescanes the image on the computer. There really is no argument if you tumble on to how LCDs work. There is no scanning. Pixels stare at you - on or off. The speed at which those switches occur is called response time in an LCDs spec.

That control is only applicable to CRT monitors. There is no flicker on an LCD - pixels stare - either on or off.

The only reason there is an argument in this issue is because the wrong term is used. Just remember - CRTs refresh . . . LCDs respond. And, there is nothing you can do to change the response time of an LCD - that is built in to it. For games, look for 12 ms or faster.

 

[FifthElement]

Originally posted by: corkyg
That is incorrect. You just don't understand how LCDs work.

I am well aware of how LCD monitors function.

People are confusing my comments regarding refresh rate as it?s applied to a CRT monitor. This way not my intention. I am referencing it solely to the video card vram buffer and how it functions before it sends its image to the monitor (a LCD in our case).

I fully understand a LCD contains pixels that are always on. They do not refresh, blink, oscillate, flicker, or do any other magic. This is clear. The pixels maintain their color variance unchanged until TOLD to do so.

But where and when does the LCD get its instructions from? From the video cards buffer of course (vram).

Because of how VGA (and DVI) functions, a LCD (and its pixels) must still poll or sample the video card at a certain rate for new frames held in vram. This is part of the DVI specification.

Sampling occurs by the LCD regardless of content change in the vram. If no change is detected within the vram, it does not trigger an update of the display or the specific pixels, leaving them in their unchanged state. This sample rate is typically 60Hz, or as in my case, 75Hz since my monitor allows for it.

Originally posted by: corkyg
It really makes no difference at all what you set your ViewSonics refresh rate at - it will always perform the same because it does not refresh at all.

I am not talking about performance, simply image stablility. If you feed a 60Hz LCD with 100fps of data, welcome to image tear city. By not syncing the sampling to your vram output, tearing is actually much more noticeable on a LCD due to the lack of a physical refresh rate. I can provide video samples of how v-sync can drastically effect an image ?polled? onto a LCD monitor. Those will have to wait a few days as I am currently away from home.

Although v-sync has its own issues, its ability to solve image tearing works well. Every time I view someone gaming on a LCD monitor, I can tell very quickly, with great accuracy, if they have v-sync or not (especially in a first-person game).

Till then, here is a great write-up concerning v-sync, image tearing, its benefits (and even problems it introduces regarding FPS).

 

[corkyg]

Interesting article - however, it makes no sense technologically.

"On an LCD, things work differently. Pixels on an LCD stay lit until they are told to change; they don't have to be refreshed. However, because of how VGA (and DVI) works, the LCD must still poll the video card at a certain rate for new frames. This is why LCD's still have a "refresh rate" even though they don't actually have to refresh."

I have never seen any case of tearing on an LCD nor can I create one. I know of no way to adjust vsync on an LCD - it doesn't exist.

Please provide the command/menu sequence for a Radeon card feeding an LCD digitally.

 

[FifthElement]

Originally posted by: corkyg
I have never seen any case of tearing on an LCD nor can I create one. I know of no way to adjust vsync on an LCD - it doesn't exist.

You must have exposure to very few LCDs. Spotting image tearing on a LCD is easier than on a CRT. Problem is, most people don't know what to look for and get used to the picture. In any case, re-creating them is easy.


To illustrate my point, here a two videos of UT2004. Keep an eye on the three main tree trunks in the center as it pans side to side. Watch the videos full screen to get the best effect. This was not software captured (which would defeat the purpose anyway). This is a recording done of the LCD with a digital video camera.

In the non-synced version you get severe stepping action as each portion of the trunk gets updated at a different time. When they are synced, this is no longer an issue.

Videos require Windows Media Player 9 or greater to view. Look for 'Click here to download'.

Synced video:

Here

Non-synced video:

Here

P.S. - If you wish to use these videos in other forums, please include this link to me.

The only difference between synced vs. non-synced was one setting: v-sync enabled or "Wait For Vertical Refresh" as its shown on ATi's control panel.

 

[corkyg]

Originally posted by: FifthElement
You must have exposure to very few LCDs. Spotting image tearing on a LCD is easier than on a CRT. Problem is, most people don't know what to look for and get used to the picture. In any case, re-creating them is easy. To illustrate my point, here a two videos of UT2004.

I guess you might be right - I have only owned and used 7 LCDs since 1995, and have never seen what you describe.

Your links do not play in WMP 11 - I'm not going back to 9. "C00D1197: Cannot play the file"

It still is not clear as to where v-synch is adjusted or enabled with an LCD. Where is that setting made?

I can see it referenced here as well - but where is vertical synchronization enabled or disabled?

V

I have checked every screen on the ATI Radeon Control Panel - can't find it. ???

 

[xtknight]

Originally posted by: corkyg
It still is not clear as to where v-synch is adjusted or enabled with an LCD. Where is that setting made?

It should be 'sync on vertical' or something similar in your graphics card control panel.

 

[corkyg]

Originally posted by: xtknight

Originally posted by: corkyg
It still is not clear as to where v-synch is adjusted or enabled with an LCD. Where is that setting made?

It should be 'sync on vertical' or something similar in your graphics card control panel.

See edit above. And, is this feature available with a DVI connection as opposed to analog? I only use digital with LCDs.

Follow this thread also:

vsync

 

[xtknight]

It's called "Wait for Vertical Refresh" in ATI CCC. VSync is not connection-specific. The graphics card simply makes sure that it is putting out full frames at the currently selected refresh rate.

 

[corkyg]

Originally posted by: xtknight
It's called "Wait for Vertical Refresh" in ATI CCC. VSync is not connection-specific. The graphics card simply makes sure that it is putting out full frames at the currently selected refresh rate.

I don't use ATI CCC (too layered and graphically busy) - I use the ATI Control Panel. OK - found what might be it . . .

vsync

The setting is as it has always been - and it has never resulted in any tearing of video. There are two available settings for resfresh rate for the VX900. They are 60 and 70. It has always been at 60, and that produces no problems.

 

[FifthElement]

Originally posted by: corkyg
Your links do not play in WMP 11 - I'm not going back to 9. "C00D1197: Cannot play the file"

Odd... they play on my laptop and home PC. Windows Media 10 and 11 respectively. Version 9 is not required, just the minimum.

According to Microsoft, that error is a connection problem, not codec problem. See Here.

They are not meant for streaming. Download them locally.

 

[corkyg]

Originally posted by: FifthElement
[Odd... they play on my laptop and home PC. Windows Media 10 and 11 respectively. Version 9 is not required, just the minimum. According to Microsoft, that error is a connection problem, not codec problem. They are not meant for streaming. Download them locally.

OK - today those links take one to a web hosting service - not to any video matierial. It works for you because you are a subscriber. Why not just do a screen clip of a tear and post it as a .JPG?]

Anyway - I think it is moot now - there is a vsync relationship for some types of video files - but none that I use, apparently. Appreciate the effort!