When HDMI first appeared more than 20 years ago, it set a new standard for high-definition home entertainment. Today, HDMI — which stands for ‘High-Definition Multimedia Interface’ — remains among the most popular digital interfaces used to transmit high-definition video and audio signals over a single cable.

HDMI cables connect the output from any number of HD sources (streaming devices, soundbars, games consoles, etc.) to the input of an HD display, such as a high-definition TV or projector. Since you probably use at least one of these devices on a daily basis, chances are that you’ve already plugged in an HDMI cable without even knowing it.

In this guide, we’ll give you a brief introduction to HDMI. We’ll also walk you through the basics of HDMI ARC and HDMI eARC, two audio-focused technologies that simplify your life by reducing the cables needed to connect your TV to a compatible home theatre soundbar.

What is HDMI?

To understand what HDMI is and what it does, it helps to simply break down the acronym:

High-Definition (HD):

The best new TVs support stunning crisp image and audio quality but higher quality means a huge amount of data. Not every cable or connection is capable of transferring all this data from an input source to your TV at the speed or bandwidth required for optimal performance. HDMI was created to solve this problem, and newer versions keep ratcheting up the bandwidth to keep pace with ever-increasing levels of video and audio quality.

Multimedia (M):

When we say “multimedia”, all we mean is that HDMI can support more than one type of media. HDMI supports both uncompressed video and multi-channel audio; that’s why we call it a multimedia interface.

Interface (I):

An interface is essentially just a connection between two devices. It’s the place where those two devices communicate and share data back and forth with each other. In this case, HDMI acts as an interface between an input device (the source of your entertainment) and an output device (the thing that plays or displays your entertainment).

OK, now let’s put it all together.

Say you have a source of audio and video data that you want to connect to your TV. This source could be a streaming device such as a Roku or Apple TV, a modern games console such as a Playstation or Xbox, or a Blu-ray player.

What you need is an interface (in other words, a physical connection) that allows you to transfer all this multimedia (i.e. audio and video) data. However, not just any interface will do. You need one that can transfer a huge amount of data at an incredibly fast rate to achieve the high-definition quality that has become standard among modern TVs, projectors, and other entertainment devices.

You may notice that we italicised some words in the above description. When you combine these words together, you get High-Definition Multimedia Interface, or HDMI. This interface is widely used to transmit digital audio and video signals across devices, and it eliminates the need for multiple cables by consolidating different signals into a single connection.

Which cable do you need for HDMI?

HDMI cables can be used to transmit uncompressed digital audio and video signals between compatible devices.

The Standard 14-millimetre HDMI cable (Type A) has 19 pins and two ‘male’ connector ends, both of which plug into ‘female’ sockets on the devices it connects. Standard HDMI cables come in varying lengths, but as a general rule, the shorter the cable, the faster the data is transferred. Once you get past 10 metres or so, you may start to see some noticeable signal degradation.

Newer versions of HDMI cables support higher data-transfer rates. These cables look like the Standard cable but are labelled High Speed or Ultra High Speed. Both are an improvement over Standard, but if you want the best possible experience with the latest HDMI 2.1 components, you may want to stick to the Ultra High Speed cable.

The good news is that these newer cables are all backward-compatible, meaning you can use them with earlier-version devices that were released before the upgrade in cable technology. The bad news is that a cable alone will not upgrade the quality of those old devices.

Note: Other types of HDMI connectors — Type B, C, D, and E — also exist for different use cases, e.g. smartphones, cameras, and vehicle entertainment systems. We’re focusing on Type A here, as it’s the standard connector for home-entertainment devices.

What is HDMI ARC?

The ARC in HDMI ARC stands for ‘Audio Return Channel’. If you use your TV with a soundbar or audio receiver, this feature helps you cut down on cables.

In a non-ARC setup, you would need a total of three cables:

• An HDMI cable to connect your source device to the audio system
• Another HDMI cable to connect your audio system to your TV
• An optical/audio cable to connect your TV back to your audio system

With HDMI ARC, you can eliminate this third cable. This is because the HDMI cable that connects your audio system to your TV can also send the TV audio back into your audio system. Instead of having two one-way roads, you’re essentially combining them into a single two-lane data highway.

ARC is not necessary if you only plan to use your TV’s speakers but if you want to use an external speaker, it not only eliminates the need for an extra cable, but also improves the sound quality of the signal by allowing the same signal to travel in both directions (to and from the speaker).

Which cable do you need for HDMI ARC?

HDMI ARC is compatible with HDMI 1.4 cables and all later versions. If you’re planning to connect a Blu-ray player or any other content source with video resolutions of 1080p or higher, you should likely buy at least a High Speed HDMI cable. Before rushing out to buy a cable separately, though, note that most soundbars already come with an HDMI ARC cable in the box.

Just note that the devices you’re connecting also have to be HDMI ARC-enabled. You should see ‘ARC’ clearly marked on the HDMI port of your TV or source device if it’s compatible.

What is HDMI eARC?

HDMI eARC stands for HDMI ‘Enhanced Audio Return Channel’.

The eARC standard was introduced in the latest version of HDMI (HDMI 2.1). It works in much the same way as HDMI ARC, though it boasts even higher audio bandwidth.

This extra bandwidth allows eARC to support higher-quality surround sound technologies. For example, though most Dolby Atmos audio can be played through HDMI ARC, you’ll need HDMI eARC to play lossless Dolby Atmos audio using the Dolby TrueHD codec.

You typically don’t have to do anything special to enable HDMI eARC; simply connect the HDMI cable as you normally would. If your TV or projector supports eARC, you may see an ‘eARC/ARC’ or similar label on its HDMI port. If you don’t see this label, check the user guide to confirm if eARC is supported.

Which cable do you need for HDMI eARC?

You don’t necessarily need a special cable for HDMI eARC, though a High Speed HDMI cable or an Ultra High Speed HDMI cable is probably a good bet. The latter option is sure to work, as the Ultra High Speed specifications support all HDMI 2.1 features.

As is the case with all newer HDMI cables, the Ultra High Speed cable is backwards-compatible with devices that don’t support HDMI 2.1.

Which is best for home theatre?

If you’re using external speakers with your home theatre system and you’re concerned with maximising the quality of your audio output, HDMI eARC is the way to go. Just note that all of the components in your mix — your TV as well as your soundbar or audio system — must be eARC-compatible to ensure optimal bandwidth. Otherwise, your bandwidth may be limited by the weakest link in your system, i.e. the device that’s only compatible with ARC.

Looking for a speaker or soundbar that will help you get the most out of your home theatre experience? Take a look at an eARC-compatible soundbar such as the Sonos Arc or Sonos Beam, and level up your sound today.