Amtune Bandwidth Planning Guide For 4K120 And 8K

Bandwidth is now the first question in any AV specification, because the answer eliminates most of the products in a catalogue before price is even discussed. Working from the published standards, HDMI 2.0 carries 18Gbps of TMDS signalling, which is about 14.4Gbps of usable video; HDMI 2.1 raises the link to 48Gbps of fixed rate link, about 42.7Gbps usable; HDMI 2.2 extends that to 96Gbps for the new uncompressed modes. On the display side, DisplayPort 1.4 offers a 25.92Gbps maximum payload, while DisplayPort 2.1 in UHBR20 mode reaches 80Gbps of link rate, about 77.4Gbps of usable video, with UHBR10 and UHBR13.5 scaling that figure per lane. Against those numbers, 4K at 120Hz in 10-bit 4:4:4 needs roughly 45Gbps uncompressed. That fits HDMI 2.1 and UHBR20 without difficulty, fits UHBR13.5 only with compression, and does not fit HDMI 2.0 at all.

The complication is that very few installations run source to display in one hop. A typical room is source, a short HDMI lead, a switcher, an extender or network link, a second lead, and a display, and every one of those elements has its own capability ceiling. DSC rescues many of these cases by compressing the stream by up to a third, but only when both the source and the sink negotiate it, and it is not available on HDMI 2.0 links at all. Long copper HDMI runs at high data rates are where most failures hide, because a cable sold as high speed may pass a link training check at 4K60 and fail intermittently at 4K120 or with HDR enabled. Once a run exceeds a few metres, the reliable approach is to leave baseband behind: category cable with a rated extender pair for runs inside a building, network distribution with AV-over-IP for anything campus-wide, and fibre for the long or electrically noisy spans.

Four planning rules cover most of it. Decide the target mode first, including refresh rate, chroma sampling, bit depth and HDR format, then subtract headroom of 25 to 30 per cent rather than designing to the exact ceiling. Check rated bandwidth for every device in the chain, not just resolution support, because a switcher that handles 4K60 is not automatically a switcher that handles 4K120 with HDR. Keep the HDR metadata path intact end to end, since HDR10, HDR10+ and Dolby Vision are not interchangeable and a converter that drops metadata produces the flat, washed-out picture that gets blamed on the display. Finally, keep EDID management in the routing layer, so a source that reads the wrong capability set does not negotiate down to 1080p and stay there.

Amtune products are specified by bandwidth class so the chain can be matched rather than assembled. The range includes AV switchers and HD video seamless hybrid matrices for deterministic routing, AV extenders to move high bit rate signals over category cable with EDID handling in the link, AV converters for format, scaling and colour space conversion where a legacy source or display cannot be replaced, and AV-over-IP codecs and decoders where the distance or the building layout rules out baseband. All units are manufactured under an ISO 9001 quality system and tested to CE, FCC and RoHS standards. Integrators can request bandwidth and EDID application notes, or sample units for testing against real sources, at sales@amtune.com.