Why do TVs have such high refresh rates when HDMI can only transmit up to 60hz, and most programs aren't 60fps anyway?

[Oldaccount1234123]

I see lots of TVs which are like 240hz, or up to 1000hz, but HDMI can I only send 60hz I thought? Also, aren't most films etc. 24 fps?

[niofalpha]

Fake refresh rates...

 

And HDMI 2.0 Supports 144 Hz.

[Arty]

Just now, niofalpha said:

Fake refresh rates.

They might be fake, but it still looks hella sweet. 

[Glenwing]

Quote

The first thing that needs to be made clear is that “Hertz” is a generic scientific unit, and it’s used to specify the frequency of any repeating event. There are many components of the display that have frequencies associated with them. For example, the processor inside the display might run at 500 MHz. The power input might accept AC power between 50 and 60 Hz. The brightness of the backlight is usually controlled through high-speed flickering at some frequency (180-240 Hz on a typical monitor). Just because some number on a display’s spec sheet has “Hz” at the end doesn’t mean it’s the refresh frequency of the display, so if you see something in "Hz" you should at least take a moment to check if the label for that number is actually "refresh rate", or if it's something else.

 

The second thing I want to point out is that the highest-bandwidth connection available on most 1080p TVs is HDMI 1.4, which can transmit a maximum of 120 frames per second at 1080p from the device to the TV, and most TVs will only accept up to 60 frames per second anyway (120 is not officially supported by the HDMI spec so a lot of TVs won’t know how to handle it). Newer “4K” TVs use HDMI 2.0, which caps out at 60 Hz at 4K. So that alone tells you that “480 Hz refresh rate” TVs can’t be using the term “refresh rate” to mean the same thing most people do.
 

Most LCD TVs are 60 Hz, even though they are marketed as “120 Hz”, “240 Hz”, “480 Hz” or above. This can mean 2 different things. Most of the time this means they use backlight strobing, which will be explained below, but in some cases it may also mean that the TV uses frame interpolation. In this case, the TV does actually operate at 120 Hz, but they still don't take more than 60 Hz input from the source, so you won't be able to set it to 120 Hz in Windows and your computer won't be sending more than 60fps to the TV. Instead, the TV takes in 60 Hz from the source, and for each pair of frames it calculates what an in-between frame might look like. Then it displays at 120 Hz, but only half the frames are received from the source, every second frame is generated by the TV itself. Since the TV isn’t actually getting any more information from the computer than it would at 60 Hz, it's still working with the same information, and it doesn’t help in gaming like a normal 120 Hz monitor. In fact the interpolation process actually adds a huge amount of latency and is really horrible for gaming, and it also completely destroys the look of movies, it is the cause of the much-maligned "soap opera effect". Turning off frame interpolation is always the very first thing you should do when you fire up a new TV, the only reason it exists is so that "120 Hz" can be printed on the box. You’re far better off with a normal 60 Hz monitor than a "120 Hz" TV for gaming.
 

Frame interpolation is only used up to 120 Hz. LCDs can't physically operate much faster than that, so if you see “240 Hz” and “480 Hz” LCD TVs, these must be using backlight strobing. They still only take in 60Hz maximum input and display at 60 Hz (or 120 Hz if they are also using frame interpolation at the same time). The "240 Hz" and "480 Hz" figures come from strobing the backlight (yes, literally just flickering the TV’s illumination source on and off) at 240 Hz/480 Hz, and they call that a “480 Hz TV”, but the display panel itself is still only refreshing at 60-120 Hz. So they advertise the flicker frequency of the backlight, and simply don't list the actual refresh frequency at all, and leave it to you to assume that the number is for the refresh rate because it's measured in "Hz". Most TV makers also come up with some kind of marketing name for the backlight flicker frequency that sounds very similar to refresh rate, like "clear motion rate" or "true motion rate"  or even "effective refresh rate", or some other meaningless nonsense like that, they're careful about not labeling it as "refresh rate" to avoid false advertising lawsuits, they just try to strongly imply that it is the refresh rate, and refuse to list the real one. If you see any weird names like that instead of "refresh rate", it should immediately tip you off that that number is not the refresh rate of the TV.
 

One more word on "600 Hz" TVs, because these are totally different; most “600 Hz” TVs you see are plasma TVs, not LCDs. Plasmas don't have backlights, so the whole backlight strobing thing above doesn't apply at all. There also aren't (to my knowledge) any plasmas that use frame interpolation. Plasma TVs have a refresh frequency of 60 Hz. The “600 Hz” number is not the refresh rate, it is the frequency of the sub-field drive (a part of standard plasma display operation). Refresh frequency is not the only thing measured in Hertz, so don’t confuse the “600 Hz” figure with the refresh frequency just because it has “Hz” at the end.
 

Plasmas are often advertised as having excellent motion clarity and salespeople try to tie this to the 600 Hz “refresh rate” but they are simply wrong and don’t understand the specs. Plasmas have excellent motion clarity because they have a very fast pixel response time (not to be confused with latency; read the first two sections of this mythbuster). It has nothing to do with the “refresh rate” or 600 Hz sub-field drive for that matter.

 

[Oldaccount1234123]

Huh, well would you look at that!