# How does a "100Hz" TV actually work? **URL:** \ **Category:** Factual Questions\ **Created:** [February 21, 2008, 2:59pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567 "2008-02-21T14:59:27Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 2:59pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/1 "2008-02-21T14:59:27Z")
I am looking to buy a new LCD HDTV which I will use mainly for watching movies. So I’m looking for a model that has the best possible picture quality for movies, in particular, one that accepts a movie picture signal at 24 frames per second and displays it in the best possible way. Now in America, they sell so-called 120Hz TVs just for this purpose. By refreshing every frame five times, the movie is displayed the exactly the way it is recorded on film. But they don’t have 120Hz TVs in Europe. They have these things called “100Hz” TV’s. How do such TV’s handle a 24fps movie signal? That is, what are the actual technical details? I’m having real trouble getting any answers to this question for the usual “100Hz” LCD TV models sold in stores. There are at least four different answers I can think of: 1. The TV does not really run at a fixed rate of 100Hz. It actually drops down to 96Hz (or increases to 120Hz) when showing a 24fps movie signal. 2. The TV inserts an extra frame every once in a while to slow down the movie. 3. European HD DVD / Blu Ray players do not actually run movies at 24fps. They run the film slightly faster at 25fps to accommodate that stupid oddball European TV refresh frequency (which is how they handle DVDs in Europe). 4. Other / none of the above. Anybody know how this actually works in typical recent consumer TVs like the Samsung LE46F86BDX? NOTE: To add to the confusion, some manufacturers use the term “100Hz” to refer to their frame interpolation algorithms. To clarify, that is NOT what I’m asking and a different subject altogether (I know these algorithms are a Bad Thing). ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 21, 2008, 4:17pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/2 "2008-02-21T16:17:12Z")
First of all, North American TVs recieve signals in NTSC format which broadcasts at 30 fps. European TV stations generally broadcast in PAL standard which is 50 fps. A computer monitor usually displays in the 60 - 90 Hz range. The short answer to your question is that, unlike a movie projector, a TV signal doesn’t flash each entire frame one by one so you won’t see any flicker caused by the frames being out of synch. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [February 21, 2008, 4:19pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/3 "2008-02-21T16:19:52Z")
Also, LCD and Plasma displays tend to have a lower refresh rate than CRTs because the pixels stay active longer. ---
**Author:** ![Rico](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rico/32/3582_2.png) [@Rico](https://boards.straightdope.com/u/Rico)\ **Post date:** [February 21, 2008, 4:23pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/4 "2008-02-21T16:23:43Z")
My WAG is: European AC line current is 50Hz. They double the refresh rate to make 100Hz. USA/Canada line current is 60Hz. Double that to 120Hz. If you were to buy a 50Hz TV it would work, but would not look “right” in that you would have lines running through the screen. The refresh rate of 100Hz would be trying to sync with the 60Hz signal and would never be in sync. ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 4:54pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/5 "2008-02-21T16:54:41Z")
PAL/NTSC doesn’t apply to my question. PAL and NTSC are analog encodings of SDTV signals. I was talking about direct digital HDTV signals, e.g. HDMI from a HD-DVD player. LCD TV’s do “flash” the frame. They don’t flash the backlight so there’s no flicker. But they still refresh the pixels at a given interval. Like you said, computer monitors (CRT as well as LCD) are distinguished by their ability to vary their refresh rate depending on the input signal (this used to be called Multisync). Question was, would a typical consumer LCD HDTV do this too? That would be the answer I was hoping for but I can’t find any confirmation of this. The 50Hz/60Hz issue exists for historical reasons but I don’t think there are any technical problems anymore with modern TVs. I have used multisync monitors on my computers for almost two decades. But do regular TVs typically have multisync capability? ---
**Author:** ![Pork\_Rind](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/pork_rind/32/111_2.png) [@Pork\_Rind](https://boards.straightdope.com/u/Pork_Rind)\ **Post date:** [February 21, 2008, 5:04pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/6 "2008-02-21T17:04:39Z")
TVs don’t actually show a film at 24fps. NTSC televisions work at 30 frames per second and PAL TVs show 25 frames per second. Both only draw every other line during a given pass, so the screen is refreshed twice as often as the frame rate. So 60 fields or 50 field per second respectively. The new TVs that use the doubled fields per second rate are just drawing the screen twice as often for smoothness or something. There isn’t any more data to display. When showing a movie that was filmed at 24FPS, at some point (before transmission or mastering the disc, usually), everything is converted to 30FPS, generally using a technique called 2:3 pull down. It works like this: > [@](#): > > An NTSC video image consists of 525 horizontal lines of information. The electron gun scans top to bottom, left to right, odd numbered lines first, then the even numbered lines. Each full scan of even numbered lines, or odd numbered lines constitutes a “field”. Each field scan takes 1/60th of a second, therefore a whole frame is scanned each 1/30th of a second. (literally 29.97 frames per second) > > Film is generally shot and projected at 24 frames per second (fps), so when film frames are converted to NTSC video, the rate must be modified to play at 29.97 fps. During the telecine process, twelve (12) fields are added to each 24 frames of film (12 fields = 6 frames) so the same images that made up 24 frames of film then comprise 30 frames of video.Video plays at a speed of 29.97 fps so the film actually runs at 23.976 fps when transferred to video. ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 5:14pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/7 "2008-02-21T17:14:05Z")
Thanks for the answers so far, but I guess my question is not clear. Let me try to reformulate. American TVs traditionally refresh 60 times per second (let’s ignore interlacing, not relevant to the question). European TVs traditionally refresh 50 times per second. Movies are traditionally shot at 24 frames per second. How do you display a movie on a TV? Like you said, traditionally an American TV converts 24 to 60 frames per second using “2:3 pulldown”. This causes a hideous distortion (“motion judder”) to the picture. That’s why they recently invented 120Hz TVs. Such a TV improves 24fps movie display by eliminating motion judder. A great improvement in movie picture quality. Traditionally an European TV displays a movie by running it at 25fps (“PAL speedup”). This is obviously a significant distortion. In Europe the recent invention is 100Hz TVs. Such a TV improves 24fps movie display by… how??? ---
**Author:** ![Alive\_At\_Both\_Ends](https://avatars.discourse-cdn.com/v4/letter/a/73ab20/32.png) [@Alive\_At\_Both\_Ends](https://boards.straightdope.com/u/Alive_At_Both_Ends)\ **Post date:** [February 21, 2008, 5:37pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/8 "2008-02-21T17:37:09Z")
[QUOTE=Frankenstein Monster] Traditionally an European TV displays a movie by running it at 25fps (“PAL speedup”). This is obviously a significant distortion. [/QUOTE] Only if you have a good musical ear. All sounds are half a semitone too high but no-one notices the speedup visually. > [@](#): > > In Europe the recent invention is 100Hz TVs. Such a TV improves 24fps movie display by… how??? Only by reducing flicker. ---
**Author:** ![FatBaldGuy](https://avatars.discourse-cdn.com/v4/letter/f/ecd19e/32.png) [@FatBaldGuy](https://boards.straightdope.com/u/FatBaldGuy)\ **Post date:** [February 21, 2008, 6:08pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/9 "2008-02-21T18:08:58Z")
The 120Hz (and 100Hz) TVs do NOT interact with 24 fps movies. As explained above, the films are converted to 30 (or 25) fps PRIOR TO BROADCAST. The only thing that a 120Hz TV will do is to display each field (2 frames) twice instead of once. You are still viewing the movie with the 2:3 pulldown (or the 25 fps speedup for PAL). ---
**Author:** ![Bambi\_Hassenpfeffer](https://avatars.discourse-cdn.com/v4/letter/b/bbe5ce/32.png) [@Bambi\_Hassenpfeffer](https://boards.straightdope.com/u/Bambi_Hassenpfeffer)\ **Post date:** [February 21, 2008, 6:19pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/10 "2008-02-21T18:19:37Z")
[QUOTE=FatBaldGuy] The 120Hz (and 100Hz) TVs do NOT interact with 24 fps movies. As explained above, the films are converted to 30 (or 25) fps PRIOR TO BROADCAST. The only thing that a 120Hz TV will do is to display each field (2 frames) twice instead of once. You are still viewing the movie with the 2:3 pulldown (or the 25 fps speedup for PAL). [/QUOTE] But he’s not talking about broadcast. As he said above, he’s talking about an HD-DVD player connected via HDMI directly to an HDTV. He wants to know how the TV displays the information coming from the DVD player – how a 100-Hz TV displays 24 fps. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 21, 2008, 6:31pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/11 "2008-02-21T18:31:02Z")
According to this: [Refresh rate - Wikipedia](http://en.wikipedia.org/wiki/Refresh_rate), the 24fps movie is sped up by 4% for use on a 50Hz or 100Hz system. ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 7:03pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/12 "2008-02-21T19:03:52Z")
Great link, **beowulff**! There’s a nice picture there at your link, under the heading “Displaying movie content on a tv”. Summarizes nicely what I know - and precisely omits the answer to my question!! Why is this info so hard to come by? The logical answer to my question would be that a 100Hz TV is not really fixed at that refresh rate. Surely technology exists that can drop down slightly to 96Hz, when fed with a 24fps signal. That is, the TV should be capable of switching between 100Hz and 96Hz. That would be basic “multisync” technology that has been around for two decades in computer monitors. And it would be the way I would design it if I were in the TV design business. But right now this is just wild speculation. Can anybody confirm or refute? ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 7:27pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/13 "2008-02-21T19:27:52Z")
[QUOTE=beowulff] According to this: [Refresh rate - Wikipedia](http://en.wikipedia.org/wiki/Refresh_rate), the 24fps movie is sped up by 4% for use on a 50Hz **or 100Hz system**. [/QUOTE] Do you have a link to confirm that European Blu-ray and HD-DVD players still speed up movies (for use on a 100Hz system)? I was under the impression that they no longer did this but I would be interested to hear otherwise. I.e. my new HD-DVD player (Toshiba HD-XE1) has a setting called “1080p/24”. Are you saying that this would actually be 1080p/25 in an European model? ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [February 21, 2008, 7:40pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/14 "2008-02-21T19:40:14Z")
Well, this says that Blu-ray doesn’t do the speed-up: [Invelos Forums: Different runningtime on BD and DVD](http://www.invelos.com/Forums.aspx?task=viewtopic&topicID=230532&messageID=498885) So, I guess you question remains unanswered. ---
**Author:** ![VunderBob](https://avatars.discourse-cdn.com/v4/letter/v/839c29/32.png) [@VunderBob](https://boards.straightdope.com/u/VunderBob)\ **Post date:** [February 21, 2008, 8:12pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/15 "2008-02-21T20:12:10Z")
The difference is that European power is 50 Hz AC; North American is 60 Hz AC. The refresh rates are derived from the fundamental frequencies of the respective power standards. ETA: Rico said the same thing. That’ll larn me to jump in without reading all of the replies… :smack: ---
**Author:** ![Frankenstein\_Monster](https://avatars.discourse-cdn.com/v4/letter/f/ccd318/32.png) [@Frankenstein\_Monster](https://boards.straightdope.com/u/Frankenstein_Monster)\ **Post date:** [February 21, 2008, 8:22pm UTC](https://boards.straightdope.com/t/how-does-a-100hz-tv-actually-work/438567/16 "2008-02-21T20:22:12Z")
OK I’m finally starting to see partial answers by googling. [This](http://www.hotukdeals.com/item/116284/toshiba-regza-37z3030d-1080p-100hz-/) is a TV that advertises both “100Hz” and “5:5 pulldown” i.e. 120Hz. Just what I was looking for but it’s just that particular model by that particular manufacturer. [Here](http://www.digitalspy.co.uk/forums/showthread.php?t=719462) is a thread on some board discussing this issue among others. Somebody says “ **the better ones** will refresh at 48/72/96 rather than use pulldown”. _Only the better ones?_ That means I really need to make sure whether my particular model is in fact one of those! Still amazed at how difficult it is to get this info!