ARC HDMI Audio Return Channel (ARC)

What ARC is

ARC — Audio Return Channel — is an HDMI feature that lets a TV send audio back to a connected AVR or soundbar over the same HDMI cable that normally carries video into the TV. It removes the need for a separate optical (TOSLINK) or coaxial digital cable when the TV itself is the source, for example for built-in streaming apps or an antenna tuner.

It was introduced as part of the HDMI 1.4 specification, released on June 5, 2009 by HDMI Licensing, LLC (the HDMI Forum was not formed until October 2011, after which it took over specification development). ARC was bundled with HDMI Ethernet Channel under the umbrella name HEAC — HDMI Ethernet and Audio Return Channel.

On the audio side, ARC carries stereo PCM and the lossy compressed codecs Dolby Digital, Dolby Digital Plus, and DTS up to 5.1 channels. Dolby Atmos can ride over ARC because Atmos metadata is embedded inside Dolby Digital Plus — but only the lossy DD+ flavor of Atmos, not the lossless TrueHD flavor used on Blu-ray.

How ARC works

ARC reuses two pins on the HDMI connector that earlier HDMI versions did not use for audio: the formerly-Reserved pin and the Hot Plug Detect pin, repurposed in HDMI 1.4 as HEAC+ and HEAC−. The same pin pair also carries the HDMI Ethernet Channel, which is why ARC and HEC are specified together as 'HEAC'.

When both features are active, the spec carries HEC as a differential signal across the HEAC+/HEAC− pair while overlaying ARC as a common-mode signal on the same wires. If only ARC is needed, a single-mode signal on HEAC+ alone is sufficient.

ARC also depends on HDMI-CEC (Consumer Electronics Control) to negotiate volume, mute, and source switching between the TV and the audio device. If CEC is disabled on either side, ARC typically stops working — which is why TVs and AVRs ship CEC under brand names like Anynet+ (Samsung), Bravia Sync (Sony), and Simplink (LG) that users often need to enable explicitly.

The audio payload itself is capped at roughly 1 Mbps. That is enough headroom for stereo PCM and the lossy 5.1 codecs (Dolby Digital, DTS, Dolby Digital Plus), but not for the higher-bandwidth lossless formats — Dolby TrueHD and DTS-HD Master Audio do not fit and cannot be passed over ARC.

One practical wrinkle: ARC is not available on every HDMI port. On both the TV and the AVR or soundbar there is one designated HDMI input/output marked 'ARC' (or 'eARC'). Plugging into a non-ARC port is one of the most common reasons audio fails to flow back to the receiver.

ARC vs eARC

eARC — Enhanced Audio Return Channel — was introduced in 2017 with the HDMI 2.1 specification, raising the audio link's bandwidth from ARC's roughly 1 Mbps to roughly 37 Mbps. That order-of-magnitude increase is what unlocks lossless formats and uncompressed multichannel audio over the same HDMI return path.

Concretely, eARC adds passthrough for the formats ARC could not carry: Dolby TrueHD, DTS-HD Master Audio, uncompressed multichannel PCM up to 32 channels at 24-bit / 192 kHz, and the lossless Dolby Atmos that rides on top of TrueHD on Blu-ray and 4K Blu-ray.

Where ARC depends on CEC for the audio handshake itself, eARC defines its own discovery and handshake protocol independent of CEC. CEC is still useful for one-remote convenience, but eARC will pass audio between an eARC TV and an eARC receiver with CEC disabled — an important reliability win, since CEC implementations are notoriously inconsistent across brands.

The 'backward compatible' framing deserves a precise reading. eARC ports gracefully fall back to ARC mode when the device on the other end only speaks ARC. The connection works and audio still flows, but the link is restricted to ARC's bandwidth and lossy 5.1 codecs — the eARC features (TrueHD, DTS-HD MA, lossless Atmos) are unavailable until both ends are eARC. So at the link level the two are compatible; at the feature level, an eARC TV paired with an ARC-only soundbar is just an ARC system.

Where ARC still appears and what it's good for

ARC remains the default audio-return mechanism on pre-2019 TVs, HDMI 1.4-era AVRs from roughly 2010 to 2018, and budget soundbars that don't carry the eARC certification. Mainstream eARC support on TVs and AVRs began arriving in 2019 model years and is now standard on mid-range and premium kit, but plenty of installed gear is still ARC-only.

For the most common audio source in a modern living room — streaming apps — ARC is genuinely sufficient. Netflix, Disney+, and Prime Video deliver Dolby Atmos inside the lossy Dolby Digital Plus container, which fits inside ARC's bandwidth budget. So a TV with built-in streaming apps and an ARC-only soundbar or AVR can still play streaming Atmos. The eARC upgrade pays off mainly when the source is a 4K Blu-ray player or a game console outputting lossless TrueHD-Atmos through the TV.

Put differently: ARC is the right answer for streaming-led setups and budget soundbars; eARC is the right answer when a disc player or a high-bitrate game audio source is in the chain and the goal is lossless multichannel audio. If the existing TV and audio device are both ARC-only, swapping HDMI cables or upgrading either end without upgrading both will not unlock TrueHD or lossless Atmos — the link will still negotiate down to ARC mode.