Thought some people might find this interesting. A recent round up at X Bit labs here reviewed a lot of the new monitors using overdrive technology (Response Time Compensation - RTC). This included several popular models from Samsung and Viewsonic and is well worth a read.
One of the most intersting points to me was the findings from the Samsung 970P where Oleg Artamanov (the reviewer) tested the response time at not only 60Hz (the normal setting) but at 75Hz refresh rate. TFT documentation always lists the "optimum" and "recommended" refresh rate at 60Hz, but it is interesting to see the effect that 75Hz had on the panel's performance.
The Samsung 970P response time under normal conditions:
A typical response time graph for an overdriven PVA / MVA panel, in this case, the 970P (at 60hz). Note the response time from code 0 to code 75 is very hard to measure because the transitions are very dark. THG don't really bother recording these in their tests. Tests are taken using a photosensor (photodiodе + low-noise operational amplifier) attached directly to the screen and taking an oscillogram while switching LCD pixels under the photosensor. This shows the response time of the pixels across the entire grey range from dark transitions on the left (code 0), to the lighter transitions on the right, reaching black > white at code 255.
At 60Hz, the graph behaves as expected and in a similar fashion to AU Optronics' 8ms P-MVA panel found here Response time is mostly around the 15ms - 20ms mark, as with Viewsonic's VP191B / VP930. Responsiveness of the panel has been improved greatly compared with old style PVA panels thanks to a heavy dose of overdrive from Samsung. Oleg says in his review:
...And at 75Hz
Using the screen with a refresh rate of 75Hz has an adverse effect on the actual performance of the panel, and the responsiveness of the pixels! This graph shows the 970P at 75Hz and you can see that the responsiveness has dropped quite considerably. This graph is much more like a traditional MVA / PVA panel would show. For comparison, the Sony HS95P's MVA panel is without overdrive and shows a similar form (here.) Now i know this is a different panel, but i just wanted to show the similarity between a non RTC monitor using MVA / PVA technology and one which does use RTC in the shape of the graph. Weirdly, at 75Hz the 970P responds like a normal PVA panel without overdrive, not as slow, but certainly not as fast as with the fully functioning overdrive. Oleg says in his review:
So what does this mean?
I spoke with Oleg as this interested me a lot. He said:
To translate a little, the LUT (Look Up Table) in this context is an algorithm used by the panel to decide how much voltage it needs to apply to the liquid crystals in order to rotate them the desired amount. The screen receives a request from the graphics card to change the image, and so then has to decide how much voltage is applied to the pixels to change to this image. At 60Hz, the LUT is capabale of sending a correct amount of voltage to the liquid crystals, and this is based on the application of overdrive, giving the panel an over impulse to speed things up. This is the principle behind overdrive, and is explained a bit more here if you want to read about it. So at 60Hz the LUT sends a good amount of overdrive driven voltage to the crystals and we get a nice responsive panel.
However, at 75Hz Oleg is suggesting that the LUT does not really operate correctly. The interface chip on the panel recognises the refresh rate is set outside of the optimum refresh rate and in trying to operate the pixels (this is in very basic terms) it cannot interpret the voltage properly. Instead, overdrive is adversely affected and the panel does not respond as quickly as it should.
Oleg has also told me that this was the first of the RTC monitors he tested at 75Hz and so cannot comment on the relevance to other models. It is quite likely that this is a common trait, particularly between other Samsung models I would imagine. He has told me he will certainly test this in any future RTC enabled monitor reviews.
Can anyone test this themselves?
Anyone with an overdriven TFT, can you test this yourselves? We obviously can't use the equipment they have at XBit or THG, but if you can compare some fast gaming then that would be excellent. Maybe try something like Pixperan (like BeHardware use) to test comparisons. Does running at 75Hz noticably decrease performance in real use to you on your screens?
hope some people found that interesting anyway
One of the most intersting points to me was the findings from the Samsung 970P where Oleg Artamanov (the reviewer) tested the response time at not only 60Hz (the normal setting) but at 75Hz refresh rate. TFT documentation always lists the "optimum" and "recommended" refresh rate at 60Hz, but it is interesting to see the effect that 75Hz had on the panel's performance.
The Samsung 970P response time under normal conditions:
A typical response time graph for an overdriven PVA / MVA panel, in this case, the 970P (at 60hz). Note the response time from code 0 to code 75 is very hard to measure because the transitions are very dark. THG don't really bother recording these in their tests. Tests are taken using a photosensor (photodiodе + low-noise operational amplifier) attached directly to the screen and taking an oscillogram while switching LCD pixels under the photosensor. This shows the response time of the pixels across the entire grey range from dark transitions on the left (code 0), to the lighter transitions on the right, reaching black > white at code 255.
At 60Hz, the graph behaves as expected and in a similar fashion to AU Optronics' 8ms P-MVA panel found here Response time is mostly around the 15ms - 20ms mark, as with Viewsonic's VP191B / VP930. Responsiveness of the panel has been improved greatly compared with old style PVA panels thanks to a heavy dose of overdrive from Samsung. Oleg says in his review:
...And at 75Hz
Using the screen with a refresh rate of 75Hz has an adverse effect on the actual performance of the panel, and the responsiveness of the pixels! This graph shows the 970P at 75Hz and you can see that the responsiveness has dropped quite considerably. This graph is much more like a traditional MVA / PVA panel would show. For comparison, the Sony HS95P's MVA panel is without overdrive and shows a similar form (here.) Now i know this is a different panel, but i just wanted to show the similarity between a non RTC monitor using MVA / PVA technology and one which does use RTC in the shape of the graph. Weirdly, at 75Hz the 970P responds like a normal PVA panel without overdrive, not as slow, but certainly not as fast as with the fully functioning overdrive. Oleg says in his review:
So what does this mean?
I spoke with Oleg as this interested me a lot. He said:
To translate a little, the LUT (Look Up Table) in this context is an algorithm used by the panel to decide how much voltage it needs to apply to the liquid crystals in order to rotate them the desired amount. The screen receives a request from the graphics card to change the image, and so then has to decide how much voltage is applied to the pixels to change to this image. At 60Hz, the LUT is capabale of sending a correct amount of voltage to the liquid crystals, and this is based on the application of overdrive, giving the panel an over impulse to speed things up. This is the principle behind overdrive, and is explained a bit more here if you want to read about it. So at 60Hz the LUT sends a good amount of overdrive driven voltage to the crystals and we get a nice responsive panel.
However, at 75Hz Oleg is suggesting that the LUT does not really operate correctly. The interface chip on the panel recognises the refresh rate is set outside of the optimum refresh rate and in trying to operate the pixels (this is in very basic terms) it cannot interpret the voltage properly. Instead, overdrive is adversely affected and the panel does not respond as quickly as it should.
Oleg has also told me that this was the first of the RTC monitors he tested at 75Hz and so cannot comment on the relevance to other models. It is quite likely that this is a common trait, particularly between other Samsung models I would imagine. He has told me he will certainly test this in any future RTC enabled monitor reviews.
Can anyone test this themselves?
Anyone with an overdriven TFT, can you test this yourselves? We obviously can't use the equipment they have at XBit or THG, but if you can compare some fast gaming then that would be excellent. Maybe try something like Pixperan (like BeHardware use) to test comparisons. Does running at 75Hz noticably decrease performance in real use to you on your screens?
hope some people found that interesting anyway