Films have been shot in 24 frames per second (24p) for many years. Since modern TVs either have a refresh rate of 60Hz or 120Hz, this creates a problem. The TV's refresh rate and the movie's frame rate don't match, causing some movement to look stuttered; you can notice it most during panning shots. This is called judder. Fortunately, most modern 4k TVs have a way to eliminate this effect.
We test our TVs to see if they can remove judder by playing a 24p video from four different sources: a native 24p source, native apps, and 60p and 60i sources. We simply check to see if a TV can remove judder from these different sources.
24p judder only matters when you watch movies because it's the only content shot in 24 frames per second; if you don’t watch movies, you have nothing to worry about.
Overall, 24p judder isn't a major problem; most people won't even notice it. If you’re wondering whether it’s an issue for you, take a look at this video and compare the look of the 24p with judder (left) to the judder-free 24p video (right). The slow-motion videos are exactly what they sound like: slowed down to show the effect of judder, but you won't see films like that anyways. If you don’t notice the judder on the left, or it doesn’t bother you, there’s no need to worry about getting a TV that can do judder-free 24p. If you do notice it and it bothers you, make a point of getting a TV that can, but most modern TVs can remove judder from at least 24p sources anyways.
TVs commonly have one of two refresh rates: 60Hz and 120Hz. 30 and 60 fps videos divide into those refresh rates evenly, making it easy for the TV panel to get the video to meet the panel refresh rate; this is what motion interpolation is for. For example, a 120Hz TV would just multiple each frame four times from a 30 fps video.
Likewise, most 120Hz panels can display 24p video without issue because 24 goes into 120 five times. However, judder is most noticeable on 60Hz TVs because 60 isn't a multiple of 24. Even if the TV doubles each frame, there are only 48 frames per second, and it's still missing 12 to reach the 60 fps needed to match the 60Hz refresh rate. So what TVs do is called the 3:2 pulldown (also called telecine): the odd-numbered frames repeat twice, and the even-numbered frames repeat three times to get 60 frames. However, this means that every second frame is held on longer than the next frame as it stays on the screen for 50 milliseconds compared to 33 ms; this causes the juddery motion. To remove judder, the TV wants to display each frame for an even amount of time.
Above is a diagram depicting the cause of judder. Frames #1 and #3 repeat twice, while frames #2 and #4 repeat three times, so they stay on the screen 50% longer.
Most TVs can remove 24p judder from native apps or native 24p sources because they receive the 24p signal and can manipulate the frames how they want. However, if a 24p video is coming from a 60Hz source, like a cable box, it's harder to remove the 24p judder because it has to try to manipulate a 60p or 60i signal. The judder itself looks the same from a native 24p source or a 60p source, but the difference is that it's harder to remove from a 60p source, and we'll explain later in this article how TVs do that.
To conduct the test, we play a 24 fps video on the TV (which you can download here). The test video cycles a white square through 24 slots in one second. While it plays, we photograph the screen, using a 1-second exposure, and you can see below what a TV looks like without judder on the left and with it on the right.
If all the boxes are the same color, it means each of the 24 slots displayed the square for the same amount of time, which the camera captures within the second of exposure, so the TV passes the test. If certain squares are light, and others are dark, it means the TV fails to play each frame for an even amount of time and therefore has judder.
We use this test to see whether a TV has judder on 24p videos sent via a 24Hz signal, like from a DVD or Blu-ray player. If you’re a big movie buff and use one of those mediums to watch movies, this test is somewhat important, but it's mostly important if you’re bothered by 24p judder. To pass this judder-free 24p test, a TV must recognize that a 24 fps video is playing and adjust its refresh rate accordingly.
The test to see if a TV removes judder from native apps is a bit more complicated, but the process the TV has to go through to remove judder from a native app is the same as a 24p source. We open a native app on the TV for our test and watch a movie (usually a Marvel movie on Netflix). We set up our high-speed camera in front and record video at 240 frames per second. We watch the video in slow motion and check if each frame is held for ten frames of the camera's video. If it is, it means the TV removes 24p judder, but if each frame is on for an uneven amount of time, it means it can't remove judder.
As explained with the photos above, if the boxes are all the same shade of gray, the TV can remove judder.
This test determines whether a TV has judder on 24p videos sent via a 60p signal. This will tell you whether movies played over a 60p signal, like streaming devices and game consoles, will have judder. If you don't like judder and watch movies over one of those devices, you should get a TV that passes this test.
This test uses the same process as the judder-free 24p test, but with the 24p video sent over a 60Hz progressive (60p) signal. To pass, a TV must recognize that a 24p video is playing over a 60p signal and adjust its refresh rate, so the video plays at 24 frames per second.
Once again, if the color of the squares in the resulting photo is not even, the TV has judder.
We also test whether a TV has judder when playing a 24p video sent via a 60Hz interlaced (60i) signal. This tells you whether movies played over a 60i signal (mainly cable & satellite boxes) will have judder. If you watch lots of movies through your cable box and don’t like the look of judder on 24p video, this is an important test for you.
This test uses the same process as the judder-free 24p test, but with the 24p video sent over a 60i signal. To pass, a TV must recognize that a 24 fps video is playing over a 60i signal and adjust its refresh rate, so the video plays at 24 frames per second.
As with the other 24p judder tests, we consider the TV judder-free if the color of squares in the test photo is the same throughout.
It's a fairly straightforward process for a TV to remove judder from 24p sources or native apps because it receives a 24p signal directly. A 60Hz TV will either drop its refresh rate down to 48Hz or slightly increase it to 72Hz so it can multiply the frames by an even number. TVs can't drop down to 24Hz, which explains why it still has to increase the frame rate to match either 48Hz or 72Hz. It's easy for 120Hz TVs to remove 24p judder because they display each frame five times.
Removing 24p judder from a 60Hz TV like a streaming box or cable box is more complicated. Firstly, the TV needs to recognize that it's playing a 24p film, then it adjusts itself to remove judder. Since the incoming video has a 3:2 pulldown and the TV can't change that, it either switches to a 48Hz or 72Hz refresh rate, then it either multiplies or triples every frame to remove the judder. We don't have a way of knowing which technique the TV is using since we would need a high-speed camera and have to check to see how many times it's refreshing. It's not necessary because we only want to know if the TV removes judder or not.
Removing 24p judder from 60p/i sources is more common on 120Hz TVs, and only a handful of 60Hz TVs can do it. There's no technical limitation as to why most 60Hz TVs can't remove judder from 60p/60i source, but since these TVs tend to be budget or entry-level models, the manufacturers may choose not to implement it.
The scoring for the judder test is based on which sources the TV can remove judder from. It scores 5.6 if it removes it from native 24p sources and 7.8 if it also removes it from native apps. Most TVs that remove it from 24p sources can also remove it from native apps, but there are a few exceptions. The TV receives a perfect score (10) if it removes judder from any source.
We don't publish our testing photo because it's not necessary. If it's judder-free, you know what the checkerboard pattern will look like, and the same can be said about the photo from TVs that can't remove judder.
Judder and stutter sound like they're the same thing, but they're not. Judder can make movement look stuttery, but it's not what real stutter is. Stutter is caused by lower-frame rate content on a TV with a fast response time as each frame holds on too long. Motion interpolation helps reduce this problem by increasing the frame rate.
Removing judder helps improve the appearance of motion with 24p movies. A few factors affect the appearance of motion on TVs, including response time, and there are other ways to improve the motion. A few of them aren't related to judder, but they're still helpful to the user.
OLED TVs can reduce the amount of persistence blur from fast-moving objects by inserting black frames in between each frame, which is why it's called black frame insertion. LED TVs don't insert frames but rather flicker the backlight, which is called backlight strobing, to help reduce motion blur. This setting is very different from judder-removal and is often used with video games and other fast-moving content. Learn more about BFI here.
Judder removal and motion interpolation are similar but different. Each setting tries to increase the frame rate to match the TV's refresh rate, but they achieve this differently. While judder changes the refresh rate of the TV to a multiple of 24 (so either 48Hz or 72Hz), motion interpolation keeps the refresh rate the same. Instead, it doubles (or quadruples) the number of frames to a higher rate (30 fps up to 60 fps), and it adds more frames in between by guessing what the frame should look like. Judder removal isn't like this because it's not adding extra frames in between; it's multiplying the same one for a longer time. Learn more about motion interpolation here.
Each of the major TV brands uses different settings names to remove judder, so we've listed them below. These settings are valid for the 2021 models, but the settings haven't changed much over the years. If you're unsure about the judder-free setting, it usually has Film, Cinema, or Theatre in the name. Keep in mind that some TVs have De-Judder or Judder Reduction settings, but these control the motion interpolation feature.
Hisense: The 2021 models automatically remove judder without any settings required. In previous years, you had to set Motion Enhancement to 'Film' to remove judder.
LG: Enable Cinema Screen. Note that their OLEDs can't remove judder if the BFI feature is flickering at 60Hz.
Samsung: No additional settings are required.
Sony: For native 24p sources, no additional settings are needed. For 60p/i sources, you need to set Cinemotion to 'High' with Motionflow to 'Custom' and the Clearness and Smoothness sliders at the minimum.
TCL: No additional settings are required.
Vizio: Enable Film Mode.
Either a TV removes judder or it doesn't, and it's out of your control, so you need to get a TV with a judder-removal feature if it bothers you. If you already have a TV and you're not sure whether it removes judder or not, check to see if there's a cinema/film setting in the motion settings. If it does, and you don't know which sources it removes judder from, it's best to watch movies from native apps or directly from a Blu-ray player because most TVs can at least remove judder from 24p sources. Should your TV not have a judder-free setting and judder bothers you, it may be your best bet to look for a new TV.
Depending on your source, you can also adjust the settings to send a 24p signal directly instead of a 60p signal, making it easier for the TV to remove judder. For example, in the video settings on Apple TV, you can select which resolution and refresh rate you want to use; select the one with 24Hz. If you have other devices go through their settings menu to see if there's anything related to it.
Judder is caused by 24p films and is noticeable in slow, panning shows where the camera doesn't look smooth. It happens because your TV displays each frame for an uneven amount of time, so some hold on longer than others. Most people won't notice it, but if you do, it can be annoying to watch a movie with judder. Our judder tests check to see a TV can remove judder from four different sources and which settings are needed to do so.