eARC vs ARC Enhanced Audio Return Channel vs Audio Return Channel

What ARC and eARC do

Both ARC (Audio Return Channel) and eARC (Enhanced Audio Return Channel) use the same physical mechanism: a dedicated audio path carried over a single HDMI cable connecting a TV to a soundbar or AV receiver (AVR). Rather than running a separate optical or analog cable for audio, the HDMI cable already used for video also carries audio in the reverse direction. From the TV back to the playback device, this lets audio that originates from cable, satellite, streaming apps, or other source devices connected directly to the TV be sent to an AVR or soundbar through that single cable, rather than requiring the TV's built-in speakers or a secondary audio connection.

eARC is the successor feature and shipped as part of the HDMI 2.1 specification.

Bandwidth ceilings

The practical difference between the two comes down to available data rate. According to DPL Laboratories' technical analysis of the eARC specification, standard ARC has a data rate of approximately 3 Mbps, sufficient for up to 5.1 channels of compressed audio. A separate secondary source (TechHive) puts ARC's usable bandwidth at around 1 Mbps. These figures come from different publications and appear to reflect different rounding conventions rather than a resolved single spec number, but both describe the same order of magnitude: a narrow pipe adequate for compressed surround sound and nothing more.

eARC raises that ceiling substantially. DPL Laboratories describes the increase as going from under 3 Mbps under ARC up to 37 Mbps (LVDS). The HDMI Forum's own blog independently states that eARC supports audio formats with up to 192kHz sampling rate and 24-bit depth, with a maximum audio bandwidth of 37 Mbits per second. This corroborates the same 37 Mbps figure from a primary-spec source rather than merely repeating DPL's number.

Format support comparison

ARC supports compressed multi-channel digital audio formats such as Dolby Digital, DTS, and MPEG-2 AAC. It does not support uncompressed high-bitrate audio such as Dolby TrueHD or DTS-HD Master Audio.

eARC enables transmission of uncompressed, multichannel PCM and high-bit-rate lossless formats such as Dolby TrueHD and DTS-HD Master Audio. Per HDMI Forum's spec-summary page, eARC supports high-bitrate audio formats up to 192kHz/24-bit, uncompressed 5.1 and 7.1 channel audio, and 32-channel uncompressed audio, in addition to DTS-HD Master Audio, DTS:X, Dolby TrueHD, and Dolby Atmos.

Common confusions

A frequent point of confusion is that Dolby Atmos can appear to work over a standard ARC-only connection. This happens because Atmos can be carried as object-based metadata layered on top of a compressed Dolby Digital Plus stream (Dolby Digital Plus with Joint Object Coding), which fits within ARC's compressed-audio bandwidth. ARC cannot, however, carry 5.1 channels of uncompressed audio or anything more than that, nor can it handle high-resolution soundtracks encoded in immersive, object-based formats such as Dolby Atmos and DTS:X in their full lossless form.

This is why lossless Atmos specifically (the version encoded inside a Dolby TrueHD stream, as found on Ultra HD Blu-ray discs) fails to pass through an ARC-only TV to an AVR or soundbar: ARC simply does not have the bandwidth for a Dolby TrueHD stream carrying Dolby Atmos, even though the lossy Dolby Digital Plus version of Atmos passes through without issue. An eARC connection is required to carry that lossless TrueHD Atmos stream intact.