60 Hz vs. 120 Hz - a quick technical explanation

[Turbonium]

So with X Hz, the screen is literally being "redrawn/refreshed" X times a second, right?

How come they didn't do this earlier? I mean, why start out at 60 Hz, only to slowly transition to 120 Hz later? Is it a technological limitation, or milking the market for all it's worth?

 

[Black Octagon]

So with X Hz, the screen is literally being "redrawn/refreshed" X times a second, right?

The short answer is yes (though that's not exactly a 'technical' explanation)

How come they didn't do this earlier? I mean, why start out at 60 Hz, only to slowly transition to 120 Hz later? Is it a technological limitation, or milking the market for all it's worth?

Who is 'they'? If you mean the monitor manufacturers, they DID. Higher refresh rates were available on quality CRTs before LCD technology even took off. 120Hz was quite rare, but quality CRTs often supported up to 75 or 85 or 100Hz.

The thing you need to keep in mind (and here comes another not-so-technical explanation) is that the refresh rate is very often tied to the monitor's resolution. On older CRTs, higher refresh rates were supported, but often only at certain resolutions. In many cases, the monitor would support a certain maximum resolution, but at that resolution you could only get so high a refresh rate. Similarly, it was also sometimes the case that the highest possible refresh rate that the monitor supported was only available at lower resolutions. I don't know the exact reason for this, but I believe it was due a combination of the CRTs monitors' own internal limitations, plus limitations of the connector bandwidth.

On LCDs, the situation is different because you basically only have 1 single 'native' resolution. In general, LCD monitors look crap when run at anything other than the native resolution. So you've got a situation in which you either want to get the highest native resolution panel that a small amount of money can afford, and refresh rates above 60Hz be damned. There are exceptions of course: more expensive TN panels can of course be bought that support both 60Hz and 120Hz natively at 1080p (with the right connectors). But such things cost money, which is why 120Hz monitors cost noticeably more. Despite all the bells and whistles you see on premium monitors like Dells and Apple Cinema Displays, the panel is the most expensive part for any monitor manufacturer to buy.

There's probably a lot more to it than that, which someone with better insider knowledge of the industry can share.

 

[Rifter]

Start out at 60hz?

What are you talking about, most CRT's could push 90hz easy with the top end ones hitting high 100's.

 

[imaheadcase]

Its all about money. You put lots of R&D into 60Hz panels, make billions of them its hard to tell investors "Yah we want to invest billions into 120Hz panels instead".

Its the same why most monitors are 1080 instead of the better 1920x1200.

 

[Borealis7]

you also need to consider the lighting in the room. if you use the "eco friendly" lightbulbs that are popular these days which produce white light then these bulbs actually flicker very fast according to the frequency of your electricity grid (50hz in europe, 60hz i think in USA).
if you have a monitor whose frequency conflicts with the lighting in the room you will see scanlines on the monitor and you're head is going to hurt.

 

[BrightCandle]

There is also a limitation in the time it takes for an LCD pixel to switch. Initially this was 25ms and it has been progressively reduced with overdrive techniques since. To begin with LCD monitors couldn't have been 120hz, the pixels just weren't switching fast enough. But often people think 60Hz is sufficient for smooth display, whereas those with these monitors know that is not the case.

 

[lamedude]

1000/120=8.3
Google says 8ms LCDs showed up around 06. I guess add a year or two before they could hit that reliably instead of the once in while marketing number.

 

[Fx1]

If you turn Vsync on and you cant hit 120fps because the game is high end and you can only get 90fps constant for example. Does this mean your monitor will run at 90FPS synced to refresh rate giving you 50% more frames per second and improve smoothness in game play?

 

[Pottuvoi]

If you turn Vsync on and you cant hit 120fps because the game is high end and you can only get 90fps constant for example. Does this mean your monitor will run at 90FPS synced to refresh rate giving you 50% more frames per second and improve smoothness in game play?

Refresh rate doesn't change depending on fps.
60hz monitor changes picture every 16.6ms and 120hz every ~8.3ms.

What 120hz monitor brings is new stable framerates like 40fps, a nice midpoint between 60 and 30.

 

[Yuriman]

Kindof. Your GPU updates a "frame buffer" as often as it can draw a frame. The contents of the frame buffer are sent to the screen at a regular interval (its refresh rate). You get tearing when the GPU is in the middle of writing to the frame buffer and the monitor queries it, because half of it is an old frame and half of it is a new frame.

At least that's how I understand it.

If your video card is rendering 30 frames per second and the monitor has a 60hz refresh rate, half of all screen refreshes will not update pixels because what's in the buffer hasn't changed. If your video card is putting out 90fps, you're likely to experience a lot of tearing since the GPU is updating the frame buffer more quickly than the monitor is querying it.

Example:

^ Unless you use double or triple buffering, which adds a 2nd or 3rd buffer and allows the video card to update the first one without causing tearing, but adds 1 or 2 full frames of latency to what you see, which is ~16 or ~33ms.

 

[Pottuvoi]

^ Unless you use double or triple buffering, which adds a 2nd or 3rd buffer and allows the video card to update the first one without causing tearing, but adds 1 or 2 full frames of latency to what you see, which is ~16 or ~33ms.

Actually normal tearing situation is already with double buffering.
The tear line is where back and front buffer are flipped.

If you only have single buffer (front buffer) you would get some seriously strange artifacts as you literally see how frame is rendered and never see the full finished image. (Haven't seen this case since Amiga500 times on workbench demo.)

 

[Yuriman]

Makes sense, thanks!

 

[Ferzerp]

Actually normal tearing situation is already with double buffering.

Yes

The tear line is where back and front buffer are flipped.

No. The tear is where the video card happened to be in the drawing process when they're flipped. Part of 2 separate buffers blended together is never presented to a monitor, but with only a single back buffer, it's constantly being drawn over top of and has a tear in it 99.9% of the time (for 1000 lines which is close enough to 1080p which is the most common resolution.)

What vsync does is holds the completed frame until it gets a chance to be displayed, and then the video card is allowed to start drawing a new one. If it doesn't finish before the next frame display cycle, instead of throwing up a torn frame, nothing changes until the next cycle.

 

[Ben90]

No. The tear is where the video card happened to be in the drawing process when they're flipped. Part of 2 separate buffers blended together is never presented to a monitor, but with only a single back buffer, it's constantly being drawn over top of and has a tear in it 99.9% of the time (for 1000 lines which is close enough to 1080p which is the most common resolution.).

The actual chance to tear is 94.4% on most 1080p monitors although it depends on the timings.

 

[Turbonium]

Start out at 60hz?

What are you talking about, most CRT's could push 90hz easy with the top end ones hitting high 100's.

I was referring to TFT displays...

Anyway, great info in this thread.

Basically, I'm trying to decide between 60 Hz and 120 Hz. Does 120 Hz literally affect how "smooth" the simplest of things look on the screen, such as a quickly moving cursor? I would imagine so, since it's redrawing twice as often per unit time.

It's a shame that virtually all 120 Hz displays are currently TN panels though...

 

[Fx1]

I was referring to TFT displays...

Anyway, great info in this thread.

Basically, I'm trying to decide between 60 Hz and 120 Hz. Does 120 Hz literally affect how "smooth" the simplest of things look on the screen, such as a quickly moving cursor? I would imagine so, since it's redrawing twice as often per unit time.

It's a shame that virtually all 120 Hz displays are currently TN panels though...

TN are good for games. 1ms response and 120hz possible. The best TN panels are not exactly inferior to any IPS panel.

IPS has better veiwing angles which isnt that important for gaming PC's

 

[biostud]

Because you need 120hz to run 3D @ 60 Hz.

 

[Black Octagon]

IPS also has better color reproduction.

OP: yes 120hz is smoother but you really need to be driving 60-120fps in game to take proper advantage of it

 

[Turbonium]

IPS also has better color reproduction.

OP: yes 120hz is smoother but you really need to be driving 60-120fps in game to take proper advantage of it

The only real "fast" games I play are older titles like Counterstrike: Source, and I'm going to be running a modern system, so 120FPS shouldn't be an issue there.

The most extreme games I'll be playing will be things like Starcraft II, everything maxed (no AA). Likely going to be on a 660 Ti or equivalent, so I think I could probably make use of 120 Hz (I'm guessing I'll easily be in the 80FPS+ range).

 

[Annisman*]

Heck, I don't care what anybody says, I can even tell the difference between 120hz and 144, I would buy a 300hz monitor if they ever made one. The more the merrier.

 

[Turbonium]

Heck, I don't care what anybody says, I can even tell the difference between 120hz and 144, I would buy a 300hz monitor if they ever made one. The more the merrier.

I don't know about that, but I can definitely tell the difference between 60 Hz and 80 Hz, up to 120 Hz. I haven't really tried beyond that.

 

[Yuriman]

Given the choice to trade my old MVA panel for a 120hz TN I'd pass without a second thought, color reproduction and great viewing angles are hard for me to give up. I'm not a competitive gamer though, and my compy really isn't fast enough to drive any modern game at 120fps. I might reconsider if I had 7970CF.

 

[nightspydk]

Hz on a crt and TN are non comparable. The time it takes the picture to refresh are dependent on screen physics and how fast the data is transmitted to the scrren Hz on a crt only concerns vertical/horizontal refreshing of the screen pixels where hz on an lcd is the speed the data is transmitted from the vga. Just pointing out we got oranges and apples tho most of you guys know.

 

[DominionSeraph]

Hz on a crt and TN are non comparable. The time it takes the picture to refresh are dependent on screen physics and how fast the data is transmitted to the scrren Hz on a crt only concerns vertical/horizontal refreshing of the screen pixels where hz on an lcd is the speed the data is transmitted from the vga. Just pointing out we got oranges and apples tho most of you guys know.

No, LCD screens update like CRT's. Send 120fps at a 60Hz LCD and you do not get a 120Hz LCD.

 

[nightspydk]

Yep send, but with a crt it's refresh a totally different matter. Read up on it mate, I gave you the short version, but the long one is out there and my interpretation is correct my friend. I do not feel like elaborating.

That's all folks.