Response Time vs Refresh Rate on LCDs - AVS Forum
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post #1 of 26 Old 04-29-2007, 11:25 AM - Thread Starter
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I see some LCD televisions like Sharp AQUOS 92 and 82 series saying that they have a refresh rate of 120hz versus 60hz. This is supposed to reduce blurring during fast image movement. I see that the Toshibas say they do 120hz through interpolation. I thought that refresh rate did not really apply to LCD televisions/moitors.

Response time or pixel fill rate or whatever, is measured in milliseconds. Most LCD's have something like 8ms or 4ms.

Which is a more important factor in having a nice smooth picture on an LCD television...response time or refresh rate.

Thanks!
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post #2 of 26 Old 04-29-2007, 02:38 PM
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Good thread! I want know the same thing too.
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post #3 of 26 Old 04-30-2007, 05:11 AM
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Is refresh rate (60hz or 120hz) and response time (8ms, 4ms) just two ways of saying the same thing? What's the difference? I'd like to know also!

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post #4 of 26 Old 04-30-2007, 06:54 AM
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They are two separate issues. Response time is the measure in time for a pixel to go from grey to white to grey. There is no particular standard for measuring this so the manufacturers are free to enhance their numbers.

Refresh rate is done syncing the picture with the line frequency at 60HZ in normal TV's. Only of late has 120HZ come into being. It doubles the refresh rate and it works in conjuction with response time. It is particularly good at fast motion and can be seen making fast moving text clear. Most rograms do not scroll the text fast enough to see the difference but I have witnessed a dew demonstratino with my previous employer that were an excellent representation of what it can do. 120HZ is some electronic trickery by dropping an interpolated frame into the picture stream for faster motion.

I know that you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant.
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post #5 of 26 Old 04-30-2007, 08:02 AM
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I have also wondered a few things about this as well. I was actually about to start a thread on it too.
What I want to know is...
Most LCDs have a 60Hz refresh. That is 1/60 = 0.01666 times per second or once every ~16ms. Using that math, it seems that as long as a pixel has a 16ms response or lower, it should be able to adaquetly change in time for each new frame.
However, most people seem to agree that 16ms is awfully high and will introduce motion blur. I usually hear people say that even the higher end LCDs with 8, 6 or even 4ms pixel response are still subject to motion blur.
So, is this just a result of manufacturers taking advantage of the no standard measurement and ramping up the numbers for pixel response.
Technically, a 8ms response should be able to change twice within the time that the next image needs to be displayed for a 60Hz refresh.
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post #6 of 26 Old 04-30-2007, 10:37 AM
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Well your normal 8ms display is only 8ms in the best of circumstances. Most 8ms displays will vary from 8ms to 24ms across the board during different scenes. Some even drop to 30ms. So this is why you begin to see motion blur. A stable 12ms panel is going to be better than a 8ms panel that will vary more.

The measurement used to be from black to white to black but was changed to the gray white gray measurement. Basically a marketing gimmick to make cheap panels appear faster. A good 8ms or 4ms panel is generally going to be capable of displaying fast motion without blur, however the video processing engine in the set also has a lot to do with how fast motion is displayed. A 4 ms off brand may have a far worse motion blur problem than a 12ms Sony Bravia.

From what I inderstand is that all of the 120hz displays that are out currently just add an extra frame in between received frames. More or less adding an extra frame buffer. This gives each pixel extra time to change reducing blur. You won't actually get 120 refreshed frames per second and I believe it is still locked to a 60 input frame per second maximum. So it is not a true 120hz display like a very high end CRT montior that would be capable of that refresh rate.
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post #7 of 26 Old 04-30-2007, 12:24 PM
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Quote:
Originally Posted by adr1978 View Post

From what I inderstand is that all of the 120hz displays that are out currently just add an extra frame in between received frames. More or less adding an extra frame buffer. This gives each pixel extra time to change reducing blur. You won't actually get 120 refreshed frames per second and I believe it is still locked to a 60 input frame per second maximum. So it is not a true 120hz display like a very high end CRT montior that would be capable of that refresh rate.

Except that a 120 Hz set can display 1080p24 without pulldown, resulting in a (supposedly) cleaner picture with no judder.

BTW, my Mitsu is 8 ms and I don't get motion blur.
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post #8 of 26 Old 04-30-2007, 01:20 PM
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RESPONSE TIME:

Strict Definition: The time required for a liquid crystal to change orientation.

Another way of saying it : The time required for a pixel to change from one luminance(light) level to another in a liquid crystal display.


REFRESH RATE:

Strict Definition: The time alloted for each frame of video to be displayed on the screen divided into one second. Active matrix displays like LCD use the entire alloted time to display a frame.
(ie - each frame of video is displayed for 16.6666ms , 1/.016666sec = 60Hz)
(ie - each frame of video is displayed for 8.3333ms , 1/.0083333sec = 120 Hz)

Another way of saying it: DISPLAY FRAME RATE (note: does not have to equal the signal frame rate)

LCD blurring is a combination of long response-times and long hold-times. Reducing the response time with overdriving techniques does not help the hold-time. Reducing the hold time by increasing the refresh rate does not change the response time. You have to do both to really reduce blur.

Big Note here: You cannot just double the refresh rate of the display from 60 to 120Hz to reduce the hold-time and hence the blurring. This is because the display will just duplicate the incoming 60Hz signal frames resulting in no change in hold time. (ie 8.3333ms + 8.3333ms = 16.6666ms). You must either add a new frame (interpolation) or add a black frame (BFI) to get any improvement in motion. Both approaches result in 120Hz refresh rate with 8.3333ms hold time.

For a detailed description see the following link :
why 120Hz?

from SID journals

"LCD Motion blur is a well known problem. Although many solutions have been proposed, some fundamental questions have not been answered yet. In this paper, we try to answer such questions. Specifically, we calculate the waveform and its blur width of a moving edge perceived on LCD screen for current LCD and the proposed four solutions of hold-type motion blur. We found that the slow response of current LCD is not a dominant factor of motion blur. The slow response of current LCD only contributes to 30% of the motion blur, while the hold-type rendering mode of LCD contributes to 70%. Therefore, fast LCD such as OCB itself does not significantly reduce motion blur. Fast LCD, on the other hand, is critical to the proposed three solutions of hold-type blur to avoid the ghosting artifact. With fast LCD, black data insertion and frame rate doubling can provide 50% reduction of motion blur. With both fast response LCD and fast backlight, backlight flashing can provide much higher reduction of motion blur. ©2005 Society for Information Display "

see paper

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post #9 of 26 Old 04-30-2007, 01:58 PM
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Another correction is that gray to white to gray is not a marketing gimick although it may sound like one. It turns out, that black to white to black smacks the LCD so hard with voltage that it actually moves. When you go from gray to white to gray, the LCD does not always move fast enough because the charge difference is so little. It actually takes longer to move gray to gray then black to white.

There is the refresh rate to the TV set. This is usually 60Hz. This is going to increase to 120Hz.

The refresh on the display is the scanning of the rows and columns of the actual LCD. THis is still 60Hz, even if the set can take 120Hz. There is work to get this to scan faster but there are things like RC constance (the LCD is a resistor/capacitor network) with limits the speed to which to get signals across the LCD.

The point to increase the refresh rate to the set is to interpolate the data. Addtionally, the LCD input electronics will be using a version of DSP(digital signal processing) and will talk to the display in different ways depending on what the image is. As the input electronics, "views" the image and will change the drive scheme to the display to "get things moving", just as the interpolation scheme will create interum screens between the real ones.
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post #10 of 26 Old 04-30-2007, 02:13 PM
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This is great information. So if I am interpreting the above information correctly, we are still basically talking about subjective measures in that manufacturers can manipulate response times and refresh rates.

Ultimately the question is going to depend more on the internal picture processor. If I am reading this information correctly, one manufacturer may claim a 6 ms response time and possibly even 120mhz refresh rates but have a substandard processor. This picture may look worse than a TV with a 8 ms response time and 60 mhz refresh rate if it uses a superior processor.

So we're kind of back to the beginning where nothing beats actually viewing and comparing. Sets can look great on paper but ultimately it comes down to internal components that most of us lay people would have no idea how to interpret.
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post #11 of 26 Old 04-30-2007, 05:09 PM
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If interpolation is used to achieve 120Hz, does it mean that I can hook up an interpolated set top box to a 60Hz TV and it too can display "120Hz"?
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post #12 of 26 Old 05-01-2007, 04:59 AM
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Quote:
Originally Posted by MitsuDude View Post

Except that a 120 Hz set can display 1080p24 without pulldown, resulting in a (supposedly) cleaner picture with no judder.

BTW, my Mitsu is 8 ms and I don't get motion blur.

Not necessarily. There are actually quite a few LCD's that cannot accept 1080P/24 and some that still have 3:2 pulldown.

I know that you believe you understand what you think I said, but I am not sure you realize that what you heard is not what I meant.
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post #13 of 26 Old 05-01-2007, 06:46 AM
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i would like to know when 120hz will move to LCD monitors (PC). not so much for the ghosting, but for the tearing (see vsync) and resulting input lag
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post #14 of 26 Old 05-01-2007, 07:16 AM
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Quote:
Originally Posted by alucard_x View Post

i would like to know when 120hz will move to LCD monitors (PC). not so much for the ghosting, but for the tearing (see vsync) and resulting input lag

Can't you just send 60hz to the monitor?
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post #15 of 26 Old 05-01-2007, 08:53 AM
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Quote:
Originally Posted by Mike53 View Post

Not necessarily. There are actually quite a few LCD's that cannot accept 1080P/24 and some that still have 3:2 pulldown.

But some can...thus my original point stands.

120 is an even multiple of 24, 30, and 60, so you can display all the HD formats with no pulldown, and therefore no judder.
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post #16 of 26 Old 01-01-2008, 03:27 PM
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OK guys...what's more important for SMOOTH BUTTERY FRAMERATES when gaming on an XBOX 360 or a PS3, lower MS under 8 or higher refresh rates like 120hz?


Im still a bit confused.....which one is better for eliminating ghosting, blurring or sluggish motion in LCD displays??
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post #17 of 26 Old 01-01-2008, 06:13 PM
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OK so my question is what if I get a new Sony 40" XBR4 with a 120Hz refresh rate will I be able to hook it up to my high end PC graphics card and display 1920x1080 @ 120Hz?? Or even 100Hz or 85hz and use it for a gaming monitor??

-Mike
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post #18 of 26 Old 01-01-2008, 06:20 PM
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Quote:
Originally Posted by DarkFudge View Post

OK guys...what's more important for SMOOTH BUTTERY FRAMERATES when gaming on an XBOX 360 or a PS3, lower MS under 8 or higher refresh rates like 120hz?


Im still a bit confused.....which one is better for eliminating ghosting, blurring or sluggish motion in LCD displays??

At 8ms, you shouldn't be seeing motion blur or ghosting. That's within the refresh rate needed to eliminate ghosting and motion blur. If the set bogs down the refresh rate at times, 8ms will turn into a higher rate, resulting in those issues.

8ms mixed with the 120hz makes things amazingly clear, IF the 8ms is locked in.


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post #19 of 26 Old 01-08-2008, 08:57 PM
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you won't be able to send 120hz from your computer to the xbr4, the highest is 60hz
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post #20 of 26 Old 01-08-2008, 09:41 PM
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Quote:
Originally Posted by ksbrent2 View Post

you won't be able to send 120hz from your computer to the xbr4, the highest is 60hz

Then, that's not really 120MHZ.
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post #21 of 26 Old 01-09-2008, 12:40 AM
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Quote:
Originally Posted by lchen5 View Post

Then, that's not really 120MHZ.

What he's trying to say is that running your computer through VGA eliminates the 120hz option, basically reverting the set to 60hz. I know it's a fact on the Samsung 71, no idea for the XBR but I'm guessing it's the same.


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post #22 of 26 Old 01-09-2008, 12:46 AM
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Quote:
Originally Posted by ScottSherNC View Post

I see some LCD televisions like Sharp AQUOS 92 and 82 series saying that they have a refresh rate of 120hz versus 60hz. This is supposed to reduce blurring during fast image movement. I see that the Toshibas say they do 120hz through interpolation. I thought that refresh rate did not really apply to LCD televisions/moitors.

Response time or pixel fill rate or whatever, is measured in milliseconds. Most LCD's have something like 8ms or 4ms.

Which is a more important factor in having a nice smooth picture on an LCD television...response time or refresh rate.

Thanks!

The answer is both. Just keep in mind that a lot of people are confusing CRT refresh rates terminology with that of LCDs. They are not the same especially in terms of computer use.

...
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post #23 of 26 Old 07-09-2008, 11:59 AM
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This thread is pretty old, but instead of making a new one with the exact same title, I figured I'd bump.

I've read through and basically summarized this thread like so:

Response time is the amount of time it takes to physically alter the liquid crystal. 8ms and below pixel response times are fast enough to eliminate some motion blur by itself. 120hz panel refresh will display 2x the amount of frames per second (compared to 60hz), and the more frames that appear on the screen, the less blurring there will be. The 120hz is really what makes the big difference in reducing overall motion blur and increasing picture clarity, not the response time (assuming it's 8ms or less).

In other words, at 120hz, you would probably not notice the difference between 8ms and 4ms.

Correct?
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post #24 of 26 Old 12-24-2008, 07:29 PM
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Quote:
Originally Posted by Shin CZ View Post

What he's trying to say is that running your computer through VGA eliminates the 120hz option, basically reverting the set to 60hz. I know it's a fact on the Samsung 71, no idea for the XBR but I'm guessing it's the same.

Why does it have to be VGA? Newer modern computers all have DVI + HDMI. I use HDMI on mine. Is this 120hz stuff all bologna through interpolation or does the panel actually support 120hz from the source? This would be good in setups that use 3d shutter glasses that actually require a 120hz display.
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post #25 of 26 Old 12-24-2008, 11:08 PM
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Quote:
Originally Posted by jayIT View Post

This thread is pretty old, but instead of making a new one with the exact same title, I figured I'd bump.

I've read through and basically summarized this thread like so:

Response time is the amount of time it takes to physically alter the liquid crystal. 8ms and below pixel response times are fast enough to eliminate some motion blur by itself. 120hz panel refresh will display 2x the amount of frames per second (compared to 60hz), and the more frames that appear on the screen, the less blurring there will be. The 120hz is really what makes the big difference in reducing overall motion blur and increasing picture clarity, not the response time (assuming it's 8ms or less).

In other words, at 120hz, you would probably not notice the difference between 8ms and 4ms.

Correct?

The primary reason for the newer 120hz panels is to reduce motion blur. LCD's refresh their pixels using the sample & hold method, which is slower than plasma and RPTV's. So, by doubling the refresh rate of the pixels, it helps compensate for the slower turnover. This helps reduce motion blur inherent to LCD technology. A 2ms spec on a 120hz LCD doesn't make it any better than an 8ms spec on a 120hz panel. The measurements are broadly attained well within legal limits. The problem with most LCD's is motion resolution, sometimes it drops way down to under 300 lines depending on the settings. This is manifested when viewing a head turning abruptly from side to side, called smearing. The VP cannot lock in like a plasma can, many plasmas retain 750 to 900 lines in motion resolution.
The VP in the Samsung, for example, is called AMP. This is primarily used to smooth judder, or the jerkyness of the camera. This is controversial because many people feel it takes away the feel of film, resulting in the soap opera look .
I have said many times that these displays are not for everyone. Also, using the low setting on AMP seems to be the best balance. Meaning it will smooth judder but have less artifacts for most sources and give you a "different" look but not as bad (if you prefer the film look). Many people love this "different" look.
For me personally, watching Pirates of the Carribean on a calibrated Sammy 650/750/850 SCP with AMP on low is a religious experience.
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post #26 of 26 Old 12-25-2008, 12:53 AM
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Quote:
Originally Posted by lipcrkr View Post

for me personally, watching pirates of the carribean on a calibrated sammy 650/750/850 scp with amp on low is a religious experience.

+1

Back off man, I'm a scientist.
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