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Pixel clock

Last response: in Graphics & Displays
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December 13, 2010 7:31:17 AM

Can a non correct pixel clock can harm the display ?

For example : An hdmi splitter is connected to the pc, so several (different manufacturer) displays are connected to the pc (same resolution).

(The splitter clones the content to the displays)

The pc sees only one generic display and sends the same pixel clock to all displays.

pixel clock manual settings can be found in : nvidia control panel > (under display) manage custom resolutions >create>advanced>Timing standard>manual

If you change settings there the pixel clock on the bottom right corner changes.

More about : pixel clock

a b Î Nvidia
December 13, 2010 9:00:54 AM

Seeing as your using an HDMI splitter, your using current LCDs on all these yes? If so, then you're going to be using 60Hz.
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December 13, 2010 9:54:44 AM

I dont know what is pixel clock yet, but its not the refresh rate.

Numbers in the pixel clock veries to my lcd screens from 120-150 ,

While the refresh rate stays constant for all lcd and is set to 60 hz (the range here is 50-60 hz , and that is not the problem).
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December 13, 2010 10:04:24 AM

The only thing (that i know of) that is different between the lcd screens is that one is 24bit (normal pc lcd) and the other is 30bit (tv lcd).

The operating system trasmit always all the time at 32bit (and thats no problem)

Other then that the two lcd are 1920X1080. but they are different manufacturers and different sizes.
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a b Î Nvidia
December 13, 2010 4:10:30 PM

So then whats your problem? I wasn't sure what you meant by "pixel clock". The only one possibility that I could come up with was the refresh rate which you claim wasn't what you were talking about but sounds to me like you were. 60Hz for monitors and "120" (or 150??) for the TV. Most 120Hz TVs simply double each frame, so they take a normal 60Hz signal just fine. The only other clock for a monitor is is the response time. 2ms, 5ms, 8ms, etc. I didn't list that as its something built into the monitor and how its connected plays no part. It simply is.

Forcing a 60Hz monitor to 85Hz, at least with CRTs, can/will destroy it. From what you've listed so far, I don't see any problem with what your doing. I've never used a splitter so I don't know if there are any problems. But so far I don't see any issues.
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December 13, 2010 4:49:26 PM

Please stop posting replies "4745454b" if you dont have an nvidia card.


In my first post is the location of the pixel clock settings in the nvidia control panel.

Here it is again : nvidia control panel > (under display) manage custom resolutions >create>advanced>Timing standard>manual

If you change settings there the pixel clock on the bottom right corner changes.

At mind time i found out what is the pixel clock. Its the bandwidth that the graphics card sends the information to the card, and it is measured in mhz.

(Not the refresh rate of the screen measured in hz).

For example I found out that bandwidth borders for vga and dvi connections are different.

So anyone with a knowledge of pixel clock bandwidth....

Do i damage a screen if its connected to a hub splitter from a pc .When the pc is seeing not a current screen but a generic screen.. then sending the lcd a different pixel

clock that it would be sending it if the lcd if would be connected directly to the oc.
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December 13, 2010 5:53:39 PM

Pixel Clock is likely similar to "Shader Clock"or "Pixel Shader Clock". This would overclock the GPU with respect to shading/lighting effects processing. This in and of itself would not harm your monitor, but COULD harm your GPU if you don't know what you're doing. There are generally three different clock speeds on your GPU:

1.) Core clock
2.) Pixel Shader Clock
3.) Memory Clock

Generally these should be adjusted with each other so that things operate in sync with each other.

The ONLY thing that would harm your monitor coming from your GPU would be forcing a higher refresh rate than the monitor can process.
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December 13, 2010 6:47:40 PM

Thank God.

And why would changing values on :

horizontal front porch, vertical front porch,horizontal synch width, vertical synch width, horizontal synch polarity, vertical synch polarity....

change the pixel clock ?


If you can explain each term (horizontal front porch, vertical front porch,horizontal synch width, vertical synch width, horizontal synch polarity, vertical synch polarity)


Reminding you i dont change the clocks, i just saw what i explained in the first post:

connecting several displays to a pc by an hdmi splitter.

"The pc sees only one generic display and (by that) sends the same pixel clock to all displays"

sending a certain display a higher pixel clock... higher then it would normaly get if it would be connected directly to the pc.
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December 13, 2010 7:14:22 PM

avb said:
Thank God.

And why would changing values on :

horizontal front porch, vertical front porch,horizontal synch width, vertical synch width, horizontal synch polarity, vertical synch polarity....

change the pixel clock ?


If you can explain each term (horizontal front porch, vertical front porch,horizontal synch width, vertical synch width, horizontal synch polarity, vertical synch polarity)


Reminding you i dont change the clocks, i just saw what i explained in the first post:

connecting several displays to a pc by an hdmi splitter.

"The pc sees only one generic display and (by that) sends the same pixel clock to all displays"

sending a certain display a higher pixel clock... higher then it would normaly get if it would be connected directly to the pc.


Please disregard everything I just said above. Doing a little research, I discovered what these terms mean. Effectively, these measurements have to do with the process of updating the screen both vertically and horizontally.

Everything starts with the sync pulse sent from the GPU to the monitor. The sync pulse keeps the monitor in time with the GPU as it sends updates to the monitor. When the GPU sends a sync pulse to the monitor, the scan line is returned to the top-left corner of the screen. Sync width is the time that it takes for the sync pulse to take place. The Front Porch is the amount of time between the last scan line on the monitor to the beginning of the next sync pulse. Sync polarity is the polarity of the electrical impulse that triggers a sync pulse. Some monitors require there to be either a drop or rise in voltage to trigger a sync pulse. All of these settings come together to allow for custom profiles with regards to monitor timing and syncronization with your graphics card.

Moral of the story: Don't adjust these settings if you don't know what you're doing. Hell, I've been working on computers for five years and just learned about this just now. I woudn't even touch them. If you ABSOLUTELY MUST TOUCH THEM, see this link to help you out: http://www.epanorama.net/faq/vga2rgb/calc.html

Changing these values could (and probably will) push your monitor out of specification and damage it.

Hope this helps and glad that I could finally get you some input on the matter. :) 
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December 14, 2010 12:25:06 AM

I am now going to find out (beside of the different pixel clock for each display)

....If the synch polarity is different for each monitor originally. ..

What happens through a splitter (clone) If the splitter sends the same polarity for a two given displays.

Well,before going on i must say that it doesnt seems logic that all the splitters (clone) out there ..damage the displays..that way.

All the computer stores are damaging the displays ???

And what about the tv box (hdmi). It doesnt have drivers to install, how does it know the polarity and the pixel clock of the destination.

Or it does know through the hdmi ?

assuming that one destination is a tv and one destination is a pc capture card. how do i know if its o.k for the capture card (is its settings like the tv) or is it upside down like the tv and the pc lcd (polarity is opposite there)?
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December 15, 2010 8:16:14 AM

I just found out through "siw" the max video bandwidth (pixel clock) of the monitors.

All is o.k here.

What about the polarity?

Does these settings can damage the display if they are different for each monitor ?

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December 15, 2010 5:54:02 PM

Chatting with nvidia technical support...

I just found out that changing these parameters doesnt

damage the dispaly.

That includes changing the polarity of the vertical/horizontal sych polarity

or even passing the maximum bandwidth of the video bandwidth (dot/pixel clock)

Although i am not going to pass the maximum video bandwidth (dot/pixel clock)
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December 15, 2010 5:55:23 PM

avb said:
Chatting with nvidia technical support...

I just found out that changing these parameters doesnt

damage the dispaly.

That includes changing the polarity of the vertical/horizontal sych polarity

or even passing the maximum bandwidth of the video bandwidth (dot/pixel clock)

Although i am not going to pass the maximum video bandwidth (dot/pixel clock)


Good to know, thanks for the info. :) 
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