Originally Posted by nimz
Quick question, does a low response time have anything to do with a TV's input lag? Just wondering because I am reading the description of a Sharp 40D68UT and it says it has a 4ms response time. Does this mean it will probably have a low input lag, or do the two have absolutely nothing to do with each other?
well they do and don't have to do with each other
they are not the same thing but they are related
pixel response time is the average time it take for a pixel to change from one state to the next, if it is too slow visual blurring and smearing occurs
it kind of goes like this and if you have a PC LCD you can visually see the blurring on ANY LCD made today because they cannot change state anywhere near fast enough for the human eye to not see smearing, plus the sample and hold nature of LCD's also tends to cause retinal blur in our eyes because there is no blanking of frames on *most* LCD's
in my own personal experience it goes like this
2-8 ms response = minimal blurring, hard to notice with normal use, with test patterns you can readily see it however
8-16 ms blurring becomes more apparent but it still does not appear to be a smear to our eyes
16-32ms smearing starts to happen and moving objects on the screen leave visible trails, if you have ever used an old color Laptop from the mid 90's you know what i'm talking about here
this response time gets stacked on top of the input lag of the display, input lag is a processing delay induced by the TV's main board and more often with today's TV's its induced by the LCD Panel's timing controller which is in charge of sending the right signals to the driver IC's that actually tell the LC's in the LCD to change state by X amount.
the reason for the timing controller (TCON for short) adding a delay is a direct result of the type of LCD, VA panels that has been chosen to be used by most TV makers due to their low cost to manufacture, easy to make in large sizes and has the best contrast and good color accuracy compared to the other types IPS and TN. what VA panel's have always lacked is fast pixel response time when it comes to changing state slightly. these panels are natively very erratic in their pixel response times and will range from 6 to 40+ ms response time to change from one state to another depending on how much they need to change (the more they need to change the faster they change due to more voltage being applied to the LC) to correct this problem manufactures invented response time compensation (RTC)
RTC is a method that can be used on ANY LCD display that literally over shoots the target voltage to force the pixel to change state faster then rapidly shoots it back to the desired point, its kind of like this if your car was very slow to get moving lets say 10 feet, this method rather than just going 10 feet it goes 200 feet past that and then straight back the other way 200 feet. of course that analogy does not work in that scenario and is insane but that is exactly what the method does with the drive voltage because this display type in particular responds much faster to large changes than it does to small changes so its much faster to overshoot and then shoot back than it is to just tell it to go 10 notches one way. this method used alone though had some serious drawbacks that can be seen in many displays, some still sold today even. it caused inverse ghosting (ghost images that appeared behind moving objects briefly) and some nasty temporary image retention (pixels that were left in a very open state for long periods of time would become used to being open and would refuse to fully close) this was reversable by turning the display off completely for long peroids of time so the LC's could loose the excess charge in them and then they would return to a fully closed state.
the solution to these problem's they discovered was to adaptively use RTC only when needed and by varying amounts, in order to accomplish this the display's TCON MUST BUFFER FRAMES!! 1 frame = 16ms on a 60hz display (everything in the US is still based around 60hz even if its a 120hz TV this does not matter much when it comes to this buffer) at first they were just buffering a frame to fix most of the problems but that still left VA TV's with ghosting problems and some Temp IR issues so they bumped it up to 2 and 3 frames to more accurately analyze incoming frames to compute how to drive the matrix to provide the best picture, 120/240hz displays with motion enhancers active (the only true time they are really making use of such high update speeds) can buffer as many as 7-8 frames in some cases causing really massive input lag that will throw lip sync off to even casual viewers without compensating on the audio feed for it. people complain about this quite often on here when they run a setup without the use of HDMI audio that will tell receivers to correct for it (TV's internal sound also automatically adjusts for delay created by the TV)
phew so now that i rambled all that out hopefully you can see how they are related and how input lag has become a major problem with LCD TV's today
the majority of the TV's are VA panels, the ones that are not are often the ones with low lag because they use IPS but this does not make them immune to the problem either because many manufactures in effort to stay with the VA displays in providing silky smooth motion enhancement they are also employing RTC on IPS panels resulting in more input lag but never on the level of the VA TV's generally speaking. Sharp's TV's are an exception, they are a sort of unique type of LCD they developed called ASV, its based on and in basic structure a VA panel but they have been able to keep input lag down when needed via game mode without hurting picture quality enough to matter to most gamers judging by owners accounts of their Sharp TV's