AN-004 · APPLICATION NOTE

High-refresh 4K from a MacBook

4K at 120 Hz or more over a single USB-C cable is real, and it fails for people constantly. The arithmetic is unforgiving: 4K120 at 8-bit color needs more bandwidth than four lanes of DisplayPort HBR3 can carry raw. It only fits with Display Stream Compression, and every link in the chain has to cooperate.

What has to be true

• The port: Apple silicon MacBooks output DisplayPort over their Thunderbolt ports; Apple documents 6K60 support, which entails HBR3 with DSC. That covers 4K120.
• The cable: all four high-speed lanes, so a full-featured or Thunderbolt/USB4 cable. The charging cable in your drawer fails here first.
• The display: must accept 4K120 over USB-C, not just over its HDMI 2.1 port. Plenty of "144 Hz USB-C" monitors take only 60 Hz on the USB-C input; the spec sheet fine print decides.

When any link falls short, nothing goes black. The display simply negotiates down to 60 Hz and most people never notice they did not get what they paid for. Run your exact pair on the bench; if we cannot verify a claim, the report says unverified rather than guessing.