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Well, the K numbers are being used as a simple shorthand for what a device (or cable) may be capable of. It's a quick substitute for a lot of other features and abilities that you could be missing out on if you rely on the wrong cable. If you have a nice 4K gaming monitor but grab the cheapest 4K cable you can find, it might limit you to 30Hz and be lousy for gaming.
That's why we've put this blog together; to help you get an idea of what 8K (or 4K or 16K) means, even when you have no intention of touching those specific K numbers. You don't want to waste money on a cable that's below (or too far above) your actual requirements. You want the Goldilocks cable.
It feels like every other blog we write mentions Bandwidth in one place or another. But when it comes to cables and equipment, bandwidth is the real measure of capability. It's a shame then, that bandwidth numbers are often hidden in favour of a flashy K number, or worse yet, the version number of the display technology. "Version 2.0" can mean little without an accompanying list of supported features. And a K rating leaves a lot unsaid, too.
HDMI and DisplayPort are the dominant AV technologies of the digital age. Using USB-C for video? That's just DisplayPort. Got a Mac with Thunderbolt? That's (fancy) DisplayPort, too. Still rocking MHL? It leverages HDMI. These two core technologies were once easily separated, but nowadays they're very similar in feature set. Typically, HDMI is for TVs and projectors, and DisplayPort is best on computers - but don't worry if your computer monitor uses HDMI. It's caught up.
The table above shows each major 'step' in bandwidth, along with its commonly associated version number(s). HDMI currently has two types of cables - High Speed and Ultra High Speed (generally both 'with Ethernet') with 18Gbps and 48Gbps being the most common available today. DisplayPort uses the HBR ratings to specify cables speeds much more precisely, and are the stats to look for.
The hardware versions are included here as a guide only, as each hardware manufacturer can choose what new features to include and which ones to ignore. A version number is no guarantee of feature support. For example, the The Xbox Series X supports HDMI 2.1, but it caps bandwidth at 40Gbps. The PS5's HDMI 2.1 spec is limited to 32Gbps. This is a function of each consoles' maximum output modes at 4K. They're not short-changing you the full 48Gbps - they're just not using it.
An 18Gbps HDMI cable is technically 4K, but only at 30Hz. In our opinion, 30Hz gets you an image that's ok for film and TV, but it's not smooth enough for productivity in the office or any kind of gaming. Let's break it down.
Everything you do with a display costs bandwidth. The top one is Resolution (the K number): the higher your resolution, the more bandwidth you need. The second big contributor is Refresh Rate, often shown in Hz or as a number after the K (e.g. 4K60). Refresh Rate and Frame Rate are related, but not the same thing. Finally, there's bit-depth or colour-depth. 10-Bit High Dynamic Range (HDR) will use a about 25% more juice than 8-bit SDR content, but there are 12-bit displays for some professional applications that need 20% more than even HDR!
As you can see, there's plenty of common (and unusual) resolutions either already on the market, or coming soon. Each of these resolutions are technically independent of refresh rate. That is to say, any resolution could run at any refresh rate you choose. In reality, there is both a bandwidth limit and a range of commonly supported combinations on most hardware. You can't always choose an in-between refresh rate to gain the maximum possible bandwidth utilisation - your video card or display will probably have set combinations. Some common ones are:
Obviously, the higher you go in refresh rate, the more bandwidth your cable will be carrying. This is roughly linear, with 60Hz needing a little more than twice the bandwidth as 30Hz at the same resolution. You should target 60Hz or above for most applications, as 30Hz is visibly inferior for all but full-motion video playback. Mouse pointers fade and blur, motion is jittery, and eye strain is exacerbated at 30Hz.
If you're running a 4K display at 120Hz with HDR, you'll be eating around 32.27Gbps, and thus need a 48Gbps HDMI "2.1" cable. A cable like this might be marketed as an 8K cable.
If you're running a 4K television and you're just watching 4K Blu-ray and Netflix, then an 18Gbps HDMI "2.0" cable will suffice. This type of cable might be marketed as a 4K cable.
If you're running a 420Hz Full HD gaming monitor in competitive eSports, that's using to about 27Gbps without HDR, and a DisplayPort HBR3 cable will get you there if your computer can use Display Stream Compression (DSC). A UHBR10 or UHBR20 cable will achieve it without DSC.
If you have an 8K television and bought it just to have a huge image for films, documentaries and television series, an 18Gbps HDMI cable will be enough for now.
If that same 8K TV is also going to be rocking some Series X, PS5 or PC gaming, then it'll be better to reach for a 48Gbps HDMI cable.
These numbers are assuming 4:4:4 chroma, or uncompressed 'full' colour. Other chroma sub-sampling methods, like 4:2:2 and 4:2:0, make the numbers above even smaller, and can help establish an image that's good enough for full motion video or diagnostics. Sub-sampling is generally not desirable when looking at images for work or gaming, so it's best to target 4:4:4 for best image.
If you find your equipment can achieve a resolution & refresh rate combination that exceeds your cable's rated bandwidth capacity, chroma sub-sampling or Display Stream Compression may be working in the background just to ensure you get a picture. You may also be losing out on High Dynamic Range, High Frame Rate or Variable Refresh Rare features.
At the end of the day, if you're happy with the image, then your cable is at least good enough for the time being. If you notice problems achieving the features you desire, it could be a bandwidth limit that's causing your woes.
We know it can be difficult to get your head around all these numbers. If you need a hand figuring out what cable is best for your specific requirements and they're not listed here, please Contact us and we'll run the numbers.
