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[xtknight]

I've heard so much mutually exclusive information about these topics. I'm on a mission to seek the truth.

Is there a hard-coded DVI pixel refresh rate (vertical frequency) limit of 60 Hz?

Single-link DVI is a max of 165 MHz, so does that mean resolution and refresh rate can be anything as long as they end up at 165 MHz? I found this equation for pixel clock on the Internet. (This is the factor referenced by 165 MHz, correct?)

Given that the vertical pixel addressability is Y, horizontal pixel addressability is X and refresh
rate is R, to account for the additional time required for the vertical blanking interval, Y is
multiplied by 1.05. The additional time required for the horizontal blanking interval is about 30% of
the scan time, so use 1.3X. Note that 30% is very conservative with most new monitors. In order
to do an exact calculation, you would have to know the vertical and horizontal blanking intervals
for the mode in question, as well as the horizontal scan frequency. So the resulting approximation
is:

BW = 1.05Y*1.3X*R
i.e. for 1280x1024 at 60 Hz, approx. bandwidth required = 1.05*1024*1.3*1280*60 = 107 MHz

If I can run my LCD at 1280x1024 and 75 Hz with a pixel clock of 135.0 MHz (as reported in OSD, and in line with that equation) that oughta mean that DVI can send 75 Hz just fine, right? Or is DVI only actually sending 60 Hz?

Does the DSP in LCDs take 75 Hz and make it 60 Hz to be compatible with the crystals? In one of the Genesis LCD controller datasheets ( http://genesis-microchip.com/products/g ... BR-01A.pdf ) I see Frame Rate Conversion (FRC) listed. Is this completely separate from the dithering method despite the similar acronym? What is frame rate conversion?

http://genesis-microchip.com/prod_lcd_mon.phtml
I notice they list black frame insertion already as one of the features. Is this currently being implemented in any LCDs?

Does the '2 FRAME' overdrive indicate that the overdrive buffer is 2 frames long ((1000/60Hz)*2 ms.)? Is that causing input lag?

Thanks! Hopefully someone knows the answer to these questions.

[Rasmus Larsen]

DVI is limited but not hard-coded. It's possible to send a 75 Hz signal but the monitor needs a 60 Hz signal.

That means that if you send a 75 Hz signal you'll end up with a 60 Hz signal anyway. The reason for your OSD to show 75 Hz is simple. The OSD measures the input signal - never the internal clock - and the input signal is 75 Hz.
I can set my ViewSonic monitor to 85 Hz as well but it'll still show 60 Hz.

The next step is HDMI. Revision 1.3 has just been released and that means that you can output far higher bandwidths and send 10, 12 and 14 bit subpixel colours.

I found this equation for pixel clock on the Internet. (This is the factor referenced by 165 MHz, correct?)

You shouldn't use it as a reference but it's a good example. If you want to know more you have to read up on "blanking".

In one of the Genesis LCD controller datasheets ( http://genesis-microchip.com/products/g ... 5861-PBR-0 1A.pdf ) I see Frame Rate Conversion (FRC) listed. Is this completely separate from the dithering method despite the similar acronym? What is frame rate conversion?

I see you found a TV controller. Frame Rate Conversion in the TV world is how you deal with the conversion from different frequencies. For example from 24 Hz to 50 Hz.

I notice they list black frame insertion already as one of the features. Is this currently being implemented in any LCDs?

I hope not =) No I'm pretty sure that it's not being implemented on large scale. It's a temporary solution. I believe that LEDs or systems like ClearLCD are far more effective. They deal with the backlight system and that's where we need improvements, both because of the colour gamut but also because we need another solution than the "Sample-and-Hold" mode.

Does the '2 FRAME' overdrive indicate that the overdrive buffer is 2 frames long ((1000/60Hz)*2 ms.)? Is that causing input lag?

It could be. I'm not sure about this, however.

[Simon Baker]

I've heard so much mutually exclusive information about these topics. I'm on a mission to seek the truth

Rasmus and I have discussed refresh rates in massive depth in the past It's an interesting area, and widely misunderstood by what people talk about on forums.

If I can run my LCD at 1280x1024 and 75 Hz with a pixel clock of 135.0 MHz (as reported in OSD, and in line with that equation) that oughta mean that DVI can send 75 Hz just fine, right? Or is DVI only actually sending 60 Hz?

As Rasmus has said, many TFT's can run fine on 75Hz (sometimes even higher!) over DVI, some need it "forced" in windows as it's not available by default. However, what the monitor needs to operate is something different to what you are sending it. There's a reason why all the manufacturers suggest 60Hz as "recommended" and "optimum" refresh rate for a TFT and it's due to how the screen itself operates.

http://genesis-microchip.com/prod_lcd_mon.phtml
I notice they list black frame insertion already as one of the features. Is this currently being implemented in any LCDs?

Interesting observation. I have avoided mentioning this next bit across various forums since I think it could lead to a lot of confusion, but Viewsonic have marketed Black Frame Insertion for a long time! Have a look at their information about ClearMotiv here, they list BFI as being an element of that technology, and this was the original documentation back when they first released overdriven panels a fair time ago!

Whether this ever was a part of ClearMotiv in practive, i'm not sure. Whether this is in the same form as that which BenQ are heavily marketing now, is another question as well.

[DVL73]

As Rasmus has said, many TFT's can run fine on 75Hz (sometimes even higher!) over DVI, some need it "forced" in windows as it's not available by default. However, what the monitor needs to operate is something different to what you are sending it. There's a reason why all the manufacturers suggest 60Hz as "recommended" and "optimum" refresh rate for a TFT and it's due to how the screen itself operates.

But in reality ... why would you run the LCD @ 75Hz anyway ?

[DVL73]

Whether this ever was a part of ClearMotiv in practive, i'm not sure. Whether this is in the same form as that which BenQ are heavily marketing now, is another question as well.

Interesting. Personally, I have my reservations about the BFI. Especially because it's based (and it's dependant) on the already established characteristics of the panel latency and overdrive control. If the BenQ will be based on the new AU Optronics "M240UW01 V0" panel,it would be interesting to see how it performs. Not sure that any other monitor is using this panel currently.

I'm more keen to see the improvements in picture quality, backlight, panel uniformity and possibly overdrive control.Somehow, I feel that this is probably more important than BFI ... which in essence is nothing revolutionary new.

[xtknight]

I'd appreciate it if someone could review my article for accuracy before I publish it on the site index. Thanks for the compliments/guidance so far.

http://library.lcdresource.com/refresh_rate.htm

[Simon Baker]

I'd appreciate it if someone could review my article for accuracy before I publish it on the site index. Thanks for the compliments/guidance so far.

http://library.lcdresource.com/refresh_rate.htm

there's a typo where you say "Besides this, many claim that DVI is not capable of transmitting a 60 Hz refresh rate" (think you mean tramsitting ABOVE 60Hz).

regarding the smoother motion @ 75Hz, the reason people want to run above 60Hz is almost always due to frame rate when Vsync is on, with people wanting to make sure they can get above 60fps. However, with technologies like tripple buffering this isn't so much of an issue as frame rate is not capped at 60fps if running at 60Hz and with vsync on. What you've said is right though, ppl do prefer 75Hz if they are playing games.

Regarding the affect on RTC, Benoit over at THG also noticed this in some of his reviews. There's more detail on it here in case you haven't seen it including some discussion I had with Oleg from X-Bit about it at the time, after Rasmus and I had discussed it a lot too

anyway, nice summary there on your site, hope the above helps a bit too

[xtknight]

Ah, good catch. The article is up now. Thanks again.