Judder on TVs Explained (Motion 5/5)

Hi, I’m Cedric from Rtings.com.
This is the last video in our series about motion and the subject is judder on TVs.
Judder is an inconsistent time frame. Or in other words, that some frames stay on the
screen longer than the other ones. Here's an exaggerated example to illustrate what
it is. Judder looks like a jerky movement that isn’t smooth.
It's important to not confuse this with stutter, which is simply caused by watching a low frame
rate content. Here's an example of a low frame rate, but without judder. It might not look
smooth, but there is no judder since the time between each frame is constant.
There are 2 main kinds of judder: the 3:2 pulldown judder and frame drops. Let's first
talk about the 3:2 pulldown judder. That kind of judder happens when you're watching
a 24 frames per second content like a movie, on a screen that refreshes 60 times per second.
24 doesn’t fit evenly in 60, so the screen will display every odd frame 3 times, and
every even frame 2 times. This 3-2 pattern will create a judder since one out of two
frames stays on the screen longer. Here's an example on a real TV in slow motion. You
can see that half the frames are displayed for a longer period of time. All phones and
tablets have that issue. Even if you are watching Netflix on your PC you will have that issue,
unless you run your monitor at a frame rate that is a multiple of 24. That kind of judder
is subtle so not everyone notice it. To test whether there is judder, we created
this pattern. It's a 24 frames per second video where the square is at each position
only one frame every second. We then take a 1 second long exposition picture with the
camera. If there is no judder, all squares will stay on the screen the same time, so
the white will be uniform. If there is judder though, all squares will have alternating
brightness. A lot of TVs are able to pass this test when
the signal sent is 24 frames per second, except a few budget TVs. A test that is harder though
is to be able to remove the judder on 24p content that is sent over 60Hz. For example,
this will be the case if you are watching a movie on an Apple TV. The Apple TV always
outputs at 60Hz, even if you are watching a 24p movie.
The TV in this case needs to do the reverse 3:2 pulldown. Which is basically detecting
the 3:2 pattern on the 60Hz signal and displaying the original 24 frames instead. This is a
lot harder to do, and very few TVs pass that test perfectly.
For example, take this Sony TV. By default, 24p works. But if I change the signal to 60p,
you can see judder on our 24p pattern. On Sony TVs, you will need to set Motionflow
to True Cinema and CineMotion to High. This won’t create the soap opera effect, but
it will force the reverse 3:2 pulldown. The second type of judder is frame drops.
Frame drops can be caused by the motion interpolation feature like we saw in the previous video.
If the movement is too fast and the TV doesn’t know how to interpolate it, it will simply
repeat the previous frame another time. This will cause judder.
Frame drops can also be caused by an app that is too slow. On some older TVs, the native
apps are not very fast, so some have problems keeping up with the streaming video, and some
might drop frames from time to time. This is usually rare though.
In conclusion, judder is due to an inconsistent time frame. If it's constant it's not called
judder but stutter. There are two types of judder, the 3:2 pulldown and frame drops.
Most TVs can get rid of the judder with the correct settings. You can see the full list
of TVs that passes this test on our website. So that's it for the motion series. If you
liked this video, subscribe to our channel, and see you next time!

Judder on TVs Explained (Motion 5/5)

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