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Why You Need A High-Refresh / 120Hz-plus Monitor

It all comes down to microtremors...

Last week we rolled out the first in a new series of why-you-need-stuff posts. The idea being, assumptions about what is good and why come a little too easily with the ongoing churn of PC hardware news and product launches. So, let's go back to basics with these assumed goodnesses. I kicked off with IPS monitor technology and while healthy discussion of the pros and cons of IPS ensued, so did some wailing and gnashing of teeth that a gaming website had appeared to be dismissive of high refresh rates and glossed over 120/144Hz.

This was because high refresh rates are a separate issue from panel type. Something worthy of a post of its own. This post, in fact. Is faster really better when it comes to screens?

Begin at the beginning

First, what exactly is a high-refresh monitor? In the context of modern LCD panels, it means a monitor capable of 120Hz or better at native resolution. That, in turn, means the screen can redraw every pixel 120 times per second.

Put another way, it means a monitor capable of truly rendering 120 individual frames per second in a game rather than simply discarding additional frames above 60 frames per second, as per a conventional flat panel screen.

120Hz is the starting point for high refresh probably because it's a simple doubling of the 60Hz refresh that has hitherto been the standard for flat panel monitors. Faster panels rated at 144Hz are also now available along with what I would call pseudo 240Hz (more on that later). No doubt even quicker monitors are forthcoming. Bigger numbers have to be better, right?

If that's the basic definition of a high-refresh panel, do these things actually work? Are such lofty refresh rates even visible to the laggardly human eye? After all, very nearly all the TV and movies you've ever seen will have been rendered at somewhere between 24 and 30 frames per second. And fluid motion is perfectly possible in those formats, isn't it?

Likewise, doesn't anything over a solid 30fps or so feel smooth in-game? What's more, the much heralded and supposedly silky smooth new HFR or high frame rate format for movies (as per the recent Hobbit money-machine trilogy) is a mere 48 frames per second and thus not even on a par with a standard PC monitor. What, then, to make of hugely higher 120Hz and beyond?

The eyes have it
There are two ways of looking at this. The first involves the science of what the human eye and brain can see and process. The second way of looking at high refresh is, well, to literally look at high refresh. Then decide for yourself whether you can tell the difference.

Until recently, really quick 144Hz panels like the Asus Rog have been exclusively TN panels...

The former is intriguing but the latter is what actually matters. If somebody has to tell you that you are looking at something new and supposedly better because otherwise you wouldn't have noticed, I'm not convinced the benefits are sufficient.

That said, for the record there are various scientific theories of the human eye and image processing in the brain that are relevant. I don't think any single element provides the full story. But one interesting component I wasn't aware of until recently involves what you might call wobble. By that I mean your eyes wobble constantly, but just a little bit. It's a process known as microtremor and in evolutionary terms it's intentional, even if intention is a misnomer in the context of evolution. But you know what I mean. The purpose or, if you prefer, consequence of microtremor, it's thought, is to increase the effective resolution of your retina, apparently doubling it.

Now it just so happens that this wobble ranges in frequency from 70Hz to just over 100Hz in humans. And that, to me, seems significant. Because in my experience mucking around with high refresh monitors, the jump from 60Hz to, say, 85Hz is subjectively substantial. Bumping things up to 100Hz makes a difference, too. But after that, well, I'd have a hard time spotting the difference between 120Hz and 144Hz in terms of fluidity, that's for sure. I'd like to see anybody reliably distinguish between the two on those terms. For me, the law of diminishing returns begins to kick in above 100Hz.

Exactly when the benefits of ever higher refresh begin to fall away will vary from person to person. But the key point is this. Refresh rates above 60Hz do make a difference. The problem is that it's one of those things you can't fully grasp without seeing it with your own eyes. But for those who haven't, it's a combination of utter fluidity and responsiveness that makes a high refresh monitor so special.

Something you can't unsee

It's also one of those things you can't unsee. Once you've experienced high refresh, you won't want to go back. Suddenly, your old 60Hz monitor will look juddery and clapped out. If you're on 60Hz and haven't seen high refresh, try this. Whip your mouse around the screen in a big circle. What you'll see is a trail of many mouse pointers as they jump across the screen in the time it takes to go from one frame to the next at 60Hz. The gap between each pointer effectively represents 1/60th of a second.

In reality, those jumps are still there at 120Hz, only smaller. But what's important is that it doesn't seem like it. At 120Hz, things seem to move like a real objects in space and time.

The same applies in-game. You have a sense of things actually moving, rather than images being rendered and animated frame by frame. In short, it peels away another layer separating you from a fuller suspension of disbelief in what you are looking at. It also makes responses to control inputs snappier. At least twice as snappy, as it happens, with a 120Hz panel, even more so with faster screens, which is the real benefit of 144Hz panels, as opposed to even greater visual fluidity.

The way to understand this point is to imagine a screen that only refreshed once a second. If you move your mouse just after the screen has updated, you'll be waiting a full second to see any reaction. The faster the refresh, the quicker a screen can respond to inputs. Simple.

Pixel response and panel type

In the context of all this speed, an inevitable question follows. How fast a panel in terms of pixel response do you need to render 120Hz? There isn't a straight forward response to this. On the one hand, with the right electronics, you could drive a very slow panel at 120Hz. On the other, the pixels wouldn't update fast enough to keep up with the refresh rate. So blurring will ensue.

Eizo's 240Hz gaming panel isn't quite what it seems...

The simple maths says 120Hz is roughly equivalent to 8ms. And that's a response time well inside a modern TN panel's specs and many newer IPS panels. Well, it is in terms of so-called grey-to-grey response. I'm not sure there's any IPS panel capable of fully switching from white to black in 8ms.

The upshot of which is that TN is better suited to high refresh than IPS (and indeed VA panels). And thus high refresh monitors kicked off with TN tech and only very recently has the industry begun to add IPS in high refresh format (the Acer panel at the top of this post is IPS and 144Hz).

The other problem with high refresh, of course, is the load it puts on your graphics subsystem. Double the refresh means double the frame rate and double the work load, which is a big ask even at 1080p, let alone higher resolutions. Even with a seriously zippy GPU, achieving a consistent 120fps at maximum detail is a huge amount of rendering. Suddenly, you may have to choose between slick 120Hz refresh and full graphics detail.

Similarly, you may have a problem simply in terms of interface bandwidth with 120Hz-plus refresh. It's more than most legacy HDMI ports on video cards can cope with at 1080p and it's beyond the remit of dual-link DVI at 2,560 by 1,440. Safe to assume you'll need a DisplayPort output.

The sordid matter of money

On the other hand, you're never actually worse off with 120Hz, and for me that's the clinching argument. It's gorgeous when it's giving you all those frames. When it isn't, you're no worse off than before. Well, not unless you've chosen TN over IPS with your 120Hz-plus panel, in which case there has been a trade off. However, now that high refresh IPS technology is appearing. I see no reason to turn it down other than cost. Acer's 27-inch, IPS, 144Hz effort, the Predator XB270HU (due to arrive in March), is nearly £700 (a USD price eludes me). But then better tech usually costs more money.

Finally, a quick word on those 240Hz panels that have popped up recently. As far as I am aware, what they're doing is frame insertion or doubling. They accept a 120Hz input and then show each frame twice. Theoretically there may be some advantage to this. It's a common ruse with HDTVs where they really go to town, ramping up a 30Hz signal to 200Hz. But in my view and for reasons I don't particularly feel the need to quantify, it's basically bollocks.

For the record, in case you're concerned by their omission, we will get to subjects such as screen tear or frame syncing later on in this series.

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Jeremy Laird