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ARC vs eARC: getting sound out of your TV correctly

Published . 7 min read

ARC and eARC use the same HDMI cable and the same labeled socket, and they are not the same pipe. ARC behaves like an S/PDIF link, so it stops at stereo PCM or compressed 5.1; eARC carries a published 37 Mbps, enough for uncompressed 7.1 and for lossless Dolby TrueHD and DTS-HD Master Audio passthrough. Nearly every "the soundbar works but I never get lossless Atmos" complaint comes down to that gap, or to a cable that carries picture while failing on the two pins the return channel needs.

ARC shipped with HDMI 1.4 on 5 June 2009, eARC with HDMI 2.1 on 28 November 2017. HDMI 2.2 is usually dated 25 June 2025, though hdmi.org's own 2.2 pages publish no release date. hdmi.org now lists eARC as an HDMI 2.2 feature rather than a 2.1-only one, without saying whether the specification changed.

Optical (S/PDIF)HDMI ARCHDMI eARC
Uncompressed PCM2 channelsstereo5.1, 7.1, to 32 channels
Compressed multichannel5.1 via IEC 61937Dolby Digital, DD+, DTS to 5.1same, plus lossless
Lossless TrueHD / DTS-HD MAnonoyes

hdmi.org's eARC page prints no bitrate anywhere. It gives the envelope verbatim: "high-bitrate audio formats up to 192kHz, 24-bit, and uncompressed 5.1 and 7.1, and 32-channel uncompressed audio", naming "DTS-HD Master Audio, DTS:X, Dolby TrueHD, Dolby Atmos".

ARC stops short by inheritance. It behaves like S/PDIF: two channels of uncompressed PCM at most, or compressed 5.1 wrapped by IEC 61937. S/PDIF "cannot support lossless surround formats that require greater bandwidth" and has no room for a DTS-HD Master Audio bitstream.

Where 37 Mbps comes from, and what to ignore

Work hdmi.org's two published ceilings and they collapse into one number:

`` 8 channels x 192,000 Hz x 24 bits = 36,864,000 bit/s 32 channels x 48,000 Hz x 24 bits = 36,864,000 bit/s ``

Both land on 36.864 Mbit/s, which rounds to the published 37 Mbps: one raw-LPCM budget you spend on either sample rate or channel count, not two independent limits.

ARC's matching figure, the "1 Mbps" headlining most articles on this subject, has no primary source and cannot be literally true: the legacy DTS core alone runs to 1.5 Mbit/s, and ARC carries DTS. Judge ARC by the formats it passes.

FormatPeak bitrateChannelseARC required
Dolby Digital (AC-3), Blu-ray640 kbit/sto 5.1no
Dolby Digital Plus (E-AC-3)0.032 to 6.144 Mbit/s1.0 to 15.1no
DTS core (legacy)1.5 Mbit/s5.1no
Dolby TrueHD, lossless18 Mbit/s16 in spec, 8 on Blu-rayyes
DTS-HD Master Audio, lossless24.5 Mbit/sup to 8yes

TrueHD is lossless through Meridian Lossless Packing at up to 192 kHz and 24-bit, and Atmos rides it inside MAT frames over HDMI 1.3 or later. DTS-HD Master Audio holds 192 kHz to 5.1, drops to 96 kHz at 6.1 and 7.1, and carries DTS:X on the same bitstream path.

Audio format peak bitrates against the eARC ceiling A bar comparison on one scale, running from zero to the eARC ceiling of 36.864 Mbit per second, published as 37 Mbps. The three formats an ARC link carries are tiny against it: Dolby Digital at 640 kbit per second, DTS core at 1.5 Mbit per second, and Dolby Digital Plus at a peak of 6.144 Mbit per second. The two lossless formats that require eARC are far larger but still fit inside the ceiling: Dolby TrueHD at 18 Mbit per second and DTS-HD Master Audio at 24.5 Mbit per second. ARC itself has no published bitrate, so it is shown by which formats it passes rather than by a bar. ARC carries this needs eARC eARC ceiling peak bitrate Dolby Digital (AC-3) 640 kbit/s DTS core (legacy) 1.5 Mbit/s Dolby Digital Plus 0.032 to 6.144 Mbit/s Dolby TrueHD 18 Mbit/s DTS-HD Master Audio 24.5 Mbit/s eARC ceiling 36.864 Mbit/s, published as 37 Mbps One scale. The ceiling is 8 channels x 192,000 Hz x 24 bits, or 32 channels x 48,000 Hz x 24 bits. ARC has no published bitrate and so has no bar here. Judge ARC by the formats it passes.
Dolby Digital Plus peaks at 6.144 Mbit/s, which is why the compressed flavor of Atmos fits an ARC link and the TrueHD flavor cannot.

Atmos is not a transport, so the logo misleads

Atmos never travels on its own. A spatially-coded sub-stream is added to Dolby TrueHD or Dolby Digital Plus, or it arrives as metadata in Dolby MAT 2.0, an LPCM-like format. Samsung's soundbar documentation splits the two cases in as many words: HDMI-eARC supports "Dolby True HD (Including Dolby Atmos uncompressed)" and "Dolby Digital Plus (Including Dolby Atmos compressed)".

So a lit Atmos indicator tells you a spatially-coded stream arrived, nothing more. The lossy Dolby Digital Plus flavor fits an ARC-class pipe. The TrueHD flavor does not, and that is the one case where eARC is mandatory rather than nice to have. Which carrier Netflix or Disney+ hands your TV is not published, so do not read the flavor off a logo.

Cables, and the pins that fail silently

ARC and eARC ride on HEAC, which uses two connector lines: the previously unused Reserved pin as HEAC+ and the Hot Plug Detect pin as HEAC-. Plain ARC can run single-ended on HEAC+ alone; HDMI Ethernet runs differentially across both.

The requirement usually quoted for eARC is an "Ultra High Speed", "Premium High Speed with Ethernet", or "High Speed with Ethernet" cable. hdmi.org's own cable page never mentions ARC or eARC, listing bandwidth tiers only, from Ultra96 at 96 Gbps down to High Speed at 10.2 Gbps. Samsung just asks for a cable marked "High Speed" or "High Speed with Ethernet".

Video does not touch the HEAC pins. A cable with a badly terminated Reserved or Hot Plug Detect pin gives a flawless 4K picture and no eARC audio. "But the video works fine" proves nothing, so swap the cable before spending an evening in menus.

Which lines in one HDMI cable carry picture and which carry return audio A schematic of a single HDMI cable between a TV socket labelled HDMI IN (eARC) and a soundbar socket labelled HDMI OUT (ARC). Three separate paths run inside the same cable. The TMDS lanes carry the picture toward the TV. Two further lines, the Reserved pin used as HEAC plus and the Hot Plug Detect pin used as HEAC minus, carry the return audio in the opposite direction, toward the soundbar. Marks on those two lines show where a bad termination sits. Because the picture path never touches them, a cable faulty there still shows a flawless 4K picture while eARC audio stays silent. one HDMI cable TV HDMI IN (eARC) Soundbar HDMI OUT (ARC) TMDS lanes carry the picture picture flows to the TV Reserved pin, used as HEAC+ these two lines carry the return audio, TV to soundbar Hot Plug Detect pin, used as HEAC- a badly terminated Reserved or Hot Plug Detect pin gives a flawless 4K picture and no eARC audio, so a working picture proves nothing Plain ARC can run single ended on HEAC+ alone. HDMI Ethernet runs differentially across both.
The two return-channel lines are the only part of the connector a picture test never exercises, which is why the cable swap belongs before the menu hunt rather than after it.

Step zero: what your brand calls CEC

One sentence explains most of the pain: CEC wiring is mandatory, but implementing CEC in a product is optional. The bus is a single-wire AV.link derivative carrying up to 15 devices at a few hundred bits per second, which is why handshakes take seconds and power-on order matters.

The rest of the pain is naming. Twenty-four trade names, eighteen vendors, one feature.

Trade nameManufacturer
Anynet+Samsung
SimpLinkLG
BRAVIA Link / BRAVIA Sync / Control for HDMISony
VIERA Link / HDAVI Control / EZ-SyncPanasonic
EasyLinkPhilips
Aquos LinkSharp
CE-Link / Regza LinkToshiba
RIHDOnkyo
Kuro LinkPioneer
NetCommand for HDMI / Realink for HDMIMitsubishi
INlinkInsignia, Westinghouse
Fun-LinkFunai, Sylvania, Emerson, Magnavox, Philips
T-LinkITT, Thomson
E-linkAOC
RuncoLinkRunco
HDMI-CECHitachi
CECHisense, Vizio
1-Touch PlayRoku

Sony and Panasonic each ship three names; Philips appears twice. Hitachi, Hisense and Vizio call it plain CEC, so a Vizio owner hunting for the equivalent of Anynet+ wants those three letters.

No sound at all

  1. Wrong socket. Samsung labels the TV input "HDMI IN (ARC)" or "HDMI IN (eARC)", and the bar's port "HDMI ARC" or "HDMI OUT". Every other TV HDMI socket is an input, not a return path.
  2. Output still on the TV speakers: Settings > Sound > Sound Output > your soundbar.
  3. eARC mode off. Samsung's switch is Settings > Sound > Expert Settings > HDMI eARC Mode, set to Auto; left off, you drop to ARC-class behavior silently.
  4. CEC disabled under a name you did not recognize.
  5. A cable without the Ethernet/HEAC capability, one with those pins badly terminated, or one that needs reseating: disconnect at both ends, reconnect, certified cables only.
  6. Handshake timing. Samsung's procedure has the TV, the bar and every source powered off before anything is connected, and warns that "muting occurs temporarily during device connection".

Before blaming the chain, isolate the panel: Home > Menu > Settings > Support > Device Care > Self Diagnosis > Sound Test. Clean sample audio there puts the fault upstream of the TV. Samsung lists a software update as a fix too.

Sound works but the format is wrong

Digital Output Audio Format decides this one. Samsung documents Auto as "the audio device automatically outputs in a supported format" and Pass-through as "audio data is output with no processing". Pick Pass-through when you want a bitstream to reach a decoder untouched; on Auto the TV may hand over something it has already processed.

If you "fixed" an ARC problem by switching to the optical output, you capped yourself below ARC: TrueHD-borne Atmos, DTS-HD Master Audio and DTS:X are all out of reach on an S/PDIF-class link.

Dialogue buried under effects that sound fine is a downmix symptom, not a volume one: collapsing multichannel to stereo folds the discrete center channel away. Voice enhance masks that; it does not correct it. Night mode, on every Samsung soundbar category from the 11.1.4ch Q-Series down to the 2.0ch Music Frame, is worth ruling out too.

Lip-sync got a standardized fix in 2025

Guides written before 2025 offer a manual audio-delay slider as the only answer to lip-sync drift. HDMI 2.2 adds the Latency Indication Protocol, which hdmi.org calls "an advancement over existing A/V sync methods for improving audio and video synchronization, especially for multiple-hop system configurations". The symptoms it names are lip movements out of step with words and misaligned footsteps or closing doors, specifically in chains running through an AV receiver or soundbar. None of that helps hardware already in your rack, but an article offering only the slider is now incomplete.

Which one to insist on

Broadcast TV and streaming apps feeding a 5.1 bar will not be limited by plain ARC, so eARC there buys headroom you never fill. Add a Blu-ray player, or a 7.1.4-class bar, and it stops being optional: TrueHD's 18 Mbit/s and DTS-HD Master Audio's 24.5 Mbit/s sit far outside an S/PDIF-class link.

The cable is also no longer the only route. LG's WOWCAST Built-In claims "up to 12 audio channels of wireless and lossless Dolby Atmos", and Samsung markets wireless Dolby Atmos on its Q-Series, Ultra Slim, All-in-One and Music Frame bars, though not on the ones sold with a separate subwoofer. Neither vendor says whether those modes still need eARC, so do not plan a build around dropping the cable.

Do not trust a spec sheet to tell you which socket to use, either. LG's page for the OLED65G5WUA, its 65-inch 2025 G5 OLED at $3,399.99 in July 2026, confirms Dolby Vision and Dolby Atmos but publishes no HDMI port count and no hint of which port carries eARC. The label on the chassis is the only reliable answer.

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