Audio Return Channel (ARC/eARC) – Explained

So what exactly does HDMI ARC do, how is it used, and do we need it? Read on.

A Little Background

The High Definition Multimedia Interface (HDMI) connection was forced upon us over 15 years ago. Over time many of its technical problems have been resolved and it has evolved into a single do-it-all connection supporting the transfer of digital video, audio and control data between various AV components. This high tech connector was to replace all those video, audio and control cables that were needed to connect your ever growing number of AV components and simplify your life. Well that was the idea! With the advent of digital technology and media, CD and DVD, unscrupulous individuals had the ability to “pirate” a perfect copy of a film or song. The HDMI connection was forced into the market by the film studios who needed a method of interconnecting equipment with an encrypted data stream that was difficult to copy; HDMI was their answer. All this has now resulted in the connection becoming the de-facto interconnect between most pieces of AV equipment.

Over the years the original HDMI version 1.0 has evolved to the current version HDMI2.1. Each evolution of the standard adding more functionality to what the data through the cable could do and support. It was HDMI version 1.4 in 2009 that introduced the HDMI Audio Return Channel (ARC).

So What is ARC and when do we need it?

ARC is a convenient way to send digital audio to an “upstream” source from a TV, amplifier or soundbar. A simple example would be a DVD player plugged into your TV but you want all the sound to be sent to a soundbar and NOT to listen to sound on the TV. If the TV has an ARC HDMI connection that socket will send any HDMI sound fed to the TV, and from the TV itself, to the sound bar. It could just as easy be a game console or set-top box that is also plugged into a TV HDMI input.

Before ARC this function could be achieved by adding a TOSlink connection to carry the audio, but as audio standards evolved TOSlink was unable to handle the increase in data bandwidth required to handle multiple uncompressed audio channels.

This way one simple HDMI ARC connection from the TV to a soundbars’ compatible HDMI ARC connection sends all audio from any device selected on the TV to the soundbar.

In order therefore to take advantage of HDMI ARC, you need a television, AV receiver or soundbar with ARC-enabled HDMI sockets. All current HDMI cables will work with ARC (NOT eARC) but you may need to go into a menu or two to set up its correct operation, like turning off the TV’s internal speakers and telling the TV to enable the ARC feature.

An additional feature that you may also want to turn on, that will reduce the number of required remotes, would be HDMI CEC (Consumer Electronics Control). This function will allow one devices remote to control other devices that are connected to it, E.G. the TV volume control controlling the sound bar volume. Be careful using CEC as sometimes it can have unintended consequences and do things that you were not expecting.

ARC Restrictions

The original ARC had a restricted data bandwidth that limited the number of audio channels and sound quality that it could carry. Also manufacturers were left to decide what audio formats their version of ARC would support and whether or not to implement lip-synch that had been introduced back in version 1.3. A real “cluster job”! The original ARC had the capacity to support:

• Stereo audio
• 5.1 Dolby Digital
• 5.1 DTS

It cannot support high bandwidth audio sources like:

• Dolby TrueHD
• Dolby Atmos
• DTS-HD Master Audio
• DTS:X

However it can usually extract the core 5.1 streams that are embedded within any Dolby Digital Plus Stream (Dolby Atmos) from services like Netflix and Amazon Prime Video.

And So Arrives The Enhanced Audio Return Channel – eARC

The following table provides a quick comparison of the various methods of audio AV interconnects:

Image Credit: HDMI.Org

Enhanced Audio Return Channel (eARC) is the next generation of ARC. It’s was implemented in the latest HDMI 2.1 specification. It is basically a much bigger data pipe that can support up to 32 channels of audio, including eight-channel, 24bit/192kHz uncompressed data streams at speeds of over 37Mbps. This huge increase in bandwidth provides support for all of the latest 4K UHD Blu-ray high definition audio formats listed above, with room to grow!!

Image Credit: Vizio

Image Credit: Samsung

This new ARC standard also improves device “handshakes” and reduces the need for HDMI CEC. Remember that BOTH devices must normally support eARC for it to work, and that just about all HDMI devices with an HDMI 2.1 certification will have an eARC connection. However, some older versioned devices may also support eARC especially as some can have their firmware upgraded.

eARC HDMI Cables

According to HDMI.org, if you currently use a standard HDMI cable with Ethernet, or a High-Speed HDMI cable with Ethernet, all should work fine. Ultra High-Speed HDMI cables with Ethernet will always work.

Because of the extra bandwidth needed for some audio formats over eARC, it’s possible that some very old cables may fail. In January 2020 HDMI.org announced a mandatory certification program to ensure any cable labelled Ultra High Speed supports all HDMI 2.1 features including eARC.

Finally ARC Compatibility

eARC is only backwards compatible with ARC to the extent that an ARC device maybe able to extract the lower bandwidth audio core from a given format. So backwards compatibility is somewhat of a “role of the dice”.

Despite some AV receivers and soundbars not having HDMI 2.1 chip sets a number of manufacturers have/are releasing firmware upgrades that will support eARC. Contact your manufactures or look on their web site for more information.