Quick answer: Resolution alone does not describe a 4K signal. The cable carries pixels times refresh times bit depth, so 3840 x 2160 at 60 Hz needs about 11.9 Gbit/s while the same frame at 120 Hz with 10-bit colour needs about 29.9 Gbit/s. Chroma subsampling is the setting that gives way first when a link runs out of room.
Two systems both say 4K and one looks crisp while the other looks soft on fine red detail. The resolution is identical, so the difference sits in refresh rate, bit depth or chroma. Understanding how those three numbers interact makes it obvious what a cord can and cannot be blamed for.
The three numbers behind a 4K signal
Every mode is a combination of pixel count, refresh rate and bits per pixel. Multiply them and you get the raw payload. At 3840 x 2160 and 60 Hz, each frame carries 8.3 million pixels, and at 8-bit RGB each pixel costs 24 bits, which lands near 11.9 Gbit/s.
Why bit depth is not a small detail
Going from 8-bit to 10-bit colour adds two bits per channel, a 25 percent increase in data. The visible gain is smoother gradients and fewer bands in skies or dark scenes. The cost is real bandwidth, and it is the first thing to check when HDR looks worse than expected.
Chroma subsampling in plain terms
Human vision resolves brightness far better than colour, so engineers compress colour instead of light. In 4:4:4 every pixel gets its own colour sample. In 4:2:0 two pixels share one set of colour samples in each direction, cutting colour data to a quarter while brightness stays full.
When 4:2:0 is acceptable
Film and sport survive 4:2:0 well because colour changes slowly across the frame. Desktop text, thin red lines in a spreadsheet and game HUDs do not, which is why a monitor can look wrong at 4K while a film on the same screen looks fine.
| Mode | Uncompressed payload | Link needed | What gives first |
|---|
| 3840 x 2160 at 30 Hz, 8-bit | about 6.0 Gbit/s | 10.2 Gbit/s | Nothing, ample margin |
| 3840 x 2160 at 60 Hz, 8-bit | about 11.9 Gbit/s | 18 Gbit/s | Refresh drops to 30 Hz |
| 3840 x 2160 at 60 Hz, 10-bit | about 14.9 Gbit/s | 18 Gbit/s | Chroma falls to 4:2:0 |
| 3840 x 2160 at 120 Hz, 10-bit | about 29.9 Gbit/s | 48 Gbit/s | Mode refuses to engage |
Where the cable actually stops
A passive copper cord has a bandwidth ceiling set by loss in the twisted pairs, and the ceiling falls as length grows. At 2 m (6.5 ft) most well made cords reach their class comfortably. At 5 m (16 ft) the same design starts to lose margin, and at 10 m (33 ft) 4K at 60 Hz often needs an active or optical design.
Reading a failed handshake
When a mode refuses to engage, the source and display exchange capability data over a low speed channel. If the cord cannot carry that exchange cleanly, the source may offer only conservative modes. A blank screen with a live source is often a failed capability read rather than a dead cord.
Compression and why shopping got harder
Newer links can compress the signal inside the interface, which lets a 48 Gbit/s connection carry modes that would otherwise be impossible. The compression is visual lossless in most content, but it is not free of artefacts in synthetic patterns. Cord class alone does not guarantee a compressed mode will work; the source and display must both support it.
Practical scenarios
- Photo editing desk: 4K at 60 Hz in 4:4:4 matters more than HDR, because skin tones and gradients show banding first.
- Living room film setup: 4K at 60 Hz with 10-bit HDR on an 18 Gbit/s cord is a sensible balance.
- Console at high refresh: accept 4:2:0 at 120 Hz only if the panel cannot do better, and use a 48 Gbit/s cord.
- Digital signage: pick the mode by the content, since static logos hide chroma loss that scrolling text reveals.
FAQ
Does 4K resolution need a special cord?
It needs a cord that meets the link rate for the mode you use. 4K at 30 Hz runs on High Speed, while 4K at 60 Hz needs an 18 Gbit/s class.
Why does 4K look soft on text?
Often the signal is running 4:2:0 instead of 4:4:4. Check the chroma setting in the display menu, then test with a short certified cord.
Is 4K at 30 Hz still 4K?
Yes, the pixel count is identical. Motion looks less smooth, and pointer movement feels heavier, which is why desktop work usually prefers 60 Hz.
Next step
Note the exact mode in the display settings, then work out the payload from resolution, refresh and bit depth. The HDMI 2.2 cable overview covers the widest links, the short HDMI cable page suits tight installs, and the long 4K run guide explains active designs.
