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Addition of Cable Power to HDMI simplifies longer cable runs

According to the newly release HDMI 2.1a Amendment 1 specification, longer HDMI cable runs will soon be possible, even without the help of an additional power source. Amendment 1 introduces “Cable Power,” a feature that lets an HDMI source device, like an A/V receiver, game console, or streaming media device, provide the additional power needed to keep a signal strong enough to survive a journey that extends further than a few meters.

If you’re raising an eyebrow right now because you’re already using a really long HDMI cable with no problems, it might be because you’re only sending lower-bandwidth content, like 4K video at 30Hz, possibly with HDR10. That kind of content only needs a Premium High Speed-rated HDMI cable, and these cables can indeed run to lengths of up to 25 feet without the need of an active cable (a cable that gets a signal boost from an external power source).

The Vizio M-Series 2.1 soundbar has two HDMI ports.
Simon Cohen / Digital Trends

However, any content that requires the full 48Gbps of an Ultra High Speed-rated cable (think uncompressed 8K@60Hz, 4K@120Hz, Dolby Vision, along with Dolby Atmos in TrueHD) will struggle to make that same trip. Cable Power has been introduced as a way to make these longer runs possible, by injecting the extra power needed from a device’s HDMI output itself, no external power sources needed.

For the new feature to work, both the source device and the HDMI cable will need to be compatible with Cable Power. Hopefully, both devices and cables will be clearly labeled so you know if they support Cable Power, but no official logo or wordmark has been created to help us quickly identify the presence of the new tech.

When using a Cable Power-capable device and cable, only one end of the cable can be plugged into the source device — this is the end that is used to receive the extra power. If you get it backward, no harm will come to your gear, but the cable will not deliver any signal at all. For those who are contemplating cable runs inside walls or other confined spaces, getting the cable ends oriented correctly will be very important.

The Monoprice RedMere HDMI cable.
A Monoprice HDMI cable with RedMere technology. Image used with permission by copyright holder

If you buy a new device that is Cable Power-enabled, you don’t have to use a Cable Power-enabled cable — the new ports are backward-compatible and your existing HDMI cables will still do what they have always done.

And, by the same token, if you decide to buy Cable Power-enabled cables — perhaps as a way of future-proofing an installation, but you don’t own any Cable Power-enabled devices yet — that’s OK too: Cable Power-enabled cables come with separate power connectors so that you can power them with a 5-volt USB adapter (typically Micro-USB or USB Type-C). You must power these cables in order for them to work, but when you eventually upgrade your source device to one that is Cable Power-enabled, you’ll be able to ditch the USB power adapter, giving you a cleaner installation.

If this sounds suspiciously like RedMere technology — which some HDMI cables use to harvest a little extra power from the source device to allow longer runs — that’s because it’s a very similar idea. The difference is that RedMere cables aren’t able to harvest enough power to allow the full bandwidth of an Ultra High Speed cable to be extended.

Curiously, even though Cable Power is an amendment to HDMI 2.1a (which itself is an update of HDMI 2.1), you’ll be able to buy a variety of speed-rated cables that support the feature. In other words, if you don’t need to send very high bandwidth content over your HDMI cable, but you still want the ability to do a really long cable run without plugging the source end of your cable into external power, you’ll be able to buy Standard, High Speed, and Premium High Speed, (in addition to Ultra High Speed) cables that support the feature.

Cable Power-enabled cables will still work with HDMI ARC/eARC, as long as they have one of the following labels:

  • Ultra High Speed HDMI Cable
  • Premium High Speed HDMI Cable with Ethernet
  • High Speed HDMI Cable with Ethernet
  • Standard HDMI Cable with Ethernet

Like the idea of Cable Power but hoping to avoid a new product purchase? Unfortunately, it looks like new hardware will be needed on the device side of the equation. A spokesperson for the HDMI Licensing Administrator tells Digital Trends that Cable Power requires chips in the source devices that will need to be manufactured specifically for that feature.

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Simon Cohen
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