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Old 02-29-08, 06:33 AM   #1
Godji
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Default Cannot get 75Hz refresh rate

Hello,

I have a 1028x1024 ViewSonic VP930 monitor connected to a 8800 GTS 512 (G92) over a DVI cable. The monitor can handle up to 75Hz at that resolution, but I cannot get anything other than 60Hz, and I can't see why. This problem appears in both 169.09 and 169.12. I have submitted a bug report, but I have not received a reply.

Maybe someone has an idea about this?
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Old 02-29-08, 07:55 AM   #2
Lethe
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Default Re: Cannot get 75Hz refresh rate

I have several VS monitors, and the optimum refresh rate for this model (and a lot, if not all, TFT monitors) is 60Hz.

I guess the EDID is working correctly and giving the what the monitor wants.

But a question. Why do you need to run @ 75Hz anyway? 60Hz is the best for TFT.

Nick
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Old 02-29-08, 08:05 AM   #3
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Default Re: Cannot get 75Hz refresh rate

Quote:
I have several VS monitors, and the optimum refresh rate for this model (and a lot, if not all, TFT monitors) is 60Hz.
Why? Besides, how do you define optimum?

Quote:
I guess the EDID is working correctly and giving the what the monitor wants.
My old video card, an NVIDIA 6600 LE, would run at 75Hz with the same monitor and xorg.conf. Even this card runs at 75Hz in Windows.

Quote:
But a question. Why do you need to run @ 75Hz anyway? 60Hz is the best for TFT.
1) I can get 75 fps with vsync in games, as opposed to 60.
2) Movies are generally ~25 fps, and 75 is a multiple of that.
3) Because my hardware can do more than 60Hz. Why run under spec?

Why do you say that 60Hz the best for TFT?

Thanks!
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Old 02-29-08, 08:13 AM   #4
Lethe
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Default Re: Cannot get 75Hz refresh rate

Because if you read the manufacturers Specs, it is DESIGNED to run at optimum of 60Hz.

Remember, TFT/LCD work totally different to the old CRT's.

Nick

**EDIT** Have a read of this:

http://www.tftcentral.co.uk/specs.htm <---- got to 'Refresh Rate' section
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Old 02-29-08, 08:55 AM   #5
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Default Re: Cannot get 75Hz refresh rate

Quote:
Originally Posted by Lethe
Because if you read the manufacturers Specs, it is DESIGNED to run at optimum of 60Hz.
You're perfectly right.

Unfortunately there is one catch. If you're in countries with 50Hz TVs/DVDs then 60Hz refresh rate is not really a good option.

Even if, in this case, I would prefer to set the video output to 50Hz and not 75Hz, unless a good quality motion compensated frame rate converter is somewhere in the system (preferably in the LCD itself).

Some few LCDs supports officially 50Hz, some others can do that, even if it is not in the specs.

bye,

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Old 02-29-08, 09:06 AM   #6
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Default Re: Cannot get 75Hz refresh rate

Alright, I'm looking that the monitor spec sheet: http://www.viewsoniceurope.com/UK/Pr...Prof/VP930.htm

I don't see anything indicating that the panel itself cannot do more than 60 Hz (as the article you pointed out would suggest) or that higher frequencies are scaled down.

In fact, the panel's bandwidth of 135 MHz corresponds to 75 Hz.

About your EDID comment: How can I see what EDID information is exchanged between the monitor and the video driver?
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Old 02-29-08, 09:10 AM   #7
Lethe
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Default Re: Cannot get 75Hz refresh rate

For EDID just check /var/log/Xorg.0.log

As to the specs, all that states is the RANGE the monitor will accept being pumped out from your graphics card - V 75Hz max - that doesn't mean it runs at that - and anything higher will result in 'signal out of range'

But honestly, 60Hz on a TFT is fine. As it says in the article I linked too, if you prefer (and can run @75Hz) and the placebo effect makes you think it is better, use it... but the VS monitor chip will cap down to 60Hz anyway.

Nick
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Old 02-29-08, 09:33 AM   #8
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Default Re: Cannot get 75Hz refresh rate

Quote:
but the VS monitor chip will cap down to 60Hz anyway
I really want to know where you know this from, for that monitor in particular.
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Old 02-29-08, 09:38 AM   #9
Lethe
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Default Re: Cannot get 75Hz refresh rate

Quote:
Originally Posted by Godji
I really want to know where you know this from, for that monitor in particular.
http://www.tftcentral.co.uk/specs.htm <--- 'Refresh Rate'

"A TFT monitor will only support refresh rates coming from your graphics card between 60Hz and 75Hz. Anything outside this will result in a "signal out of range" message or similar. The “recommended” refresh rate for a TFT is 60hz, a value which would be difficult to use on a CRT. The “maximum” refresh rate of a TFT is 75hz, but sometimes if you are using a DVI connection the refresh is capped at 60hz anyway."

Nick
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Old 03-01-08, 04:01 AM   #10
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Default Re: Cannot get 75Hz refresh rate

The keyword here is "sometimes". This says nothing about my monitor, as far as I can tell. When I play a game at 75Hz, I would be getting tearing if the monitor was truly only showing me 60Hz, but I am not. So I think it does work at 75Hz. I do appreciate your info, though.

Anyway, I want it to run at 75 Hz under Linux. Can anyone please help me out?
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Old 03-01-08, 04:05 AM   #11
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Default Re: Cannot get 75Hz refresh rate

Quote:
Originally Posted by Godji
About your EDID comment: How can I see what EDID information is exchanged between the monitor and the video driver?
start the X server with `startx -- -logverbose 6`
then you get more detail in the X logfile (/var/log/Xorg.0.log) about what EDID info is returned and what mode parameters the X server chooses.
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Old 03-01-08, 06:37 AM   #12
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Default Re: Cannot get 75Hz refresh rate

Thanks, wonderful tip!

The extended log once again shows that the server can do 75Hz, and that it thinks it has chosen a 75Hz mode and is using it, when in facts it continues to run at 60Hz.

But then, I noticed the following bit:
Code:
(II) NVIDIA(0): Native backend timings for ViewSonic VP930 Series (DFP-0): 
 (II) NVIDIA(0):   1280 x 1024 @ 60 Hz 
 (II) NVIDIA(0):     Pixel Clock      : 108.000 MHz 
 (II) NVIDIA(0):     HRes, HSyncStart : 1280, 1328 
 (II) NVIDIA(0):     HSyncEnd, HTotal : 1440, 1688 
 (II) NVIDIA(0):     VRes, VSyncStart : 1024, 1025 
 (II) NVIDIA(0):     VSyncEnd, VTotal : 1028, 1066 
 (II) NVIDIA(0):     H/V Polarity     : +/+
Lethe, is this what you were referring to, related to the fact that the monitor could not in fact do anything other than 60 Hz?
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