HDMI ARC vs eARC vs Optical: eARC Carries 37 Mbps, and Streaming Atmos Does Not Need It

Short answer: connect the soundbar’s HDMI OUT to the TV port labeled ARC or eARC, and only fall back to optical if HDMI misbehaves or the TV has no ARC port. eARC has up to 37 Mbps of audio bandwidth against roughly 1 Mbps for ARC, but that headroom matters only for lossless formats from discs, and for a few sources such as Apple TV 4K that send Atmos in a bulky form. Atmos from streaming apps travels inside Dolby Digital Plus and fits through plain ARC. Most “my soundbar sounds wrong” problems are not the cable or the port standard. They are one TV menu setting.

Find the right port first

Two labels matter, and both are printed on the hardware.

• On the TV: look for the HDMI port marked ARC or eARC. Usually only one port has it. Any other HDMI port is input-only and will never send sound out.
• On the soundbar: use the port marked HDMI OUT, TV, or HDMI (ARC/eARC). Ports marked HDMI IN are for plugging a player into the bar.

Then, in the TV’s sound menu, set the output to the HDMI ARC/eARC device (wording varies: “Receiver,” “Audio System,” “HDMI ARC”), and turn on HDMI-CEC, which ARC depends on. If the TV offers a separate eARC mode toggle, set it to Auto or On. If no sound appears, power-cycle both devices at the wall before changing anything else; the ARC handshake happens at power-up and sometimes just fails.

What each connection can carry

HDMI Licensing Administrator describes eARC as supporting audio up to 192 kHz / 24-bit, uncompressed 5.1 and 7.1, and the lossless formats Dolby TrueHD, DTS-HD Master Audio, Dolby Atmos and DTS:X. Plain ARC was specified to match what optical could do; Dolby Digital Plus over ARC came later as something TV makers chose to implement, which is why it works on the great majority of TVs but is worth confirming on an older set.

There are three kinds of Atmos, and they need different pipes

“Atmos” on a box says nothing about how the signal is packaged, and the packaging decides which connection works.

The first row is what most households actually watch, and it explains the headline: a soundbar fed by the TV’s own apps, a Roku or a Fire TV stick gets full streaming Atmos over plain ARC. It is the second and third rows where an ARC-only TV quietly drops you to Dolby Digital 5.1 or stereo with no error message.

Check Dolby Atmos soundbars with eARC on Amazon

When eARC actually matters

For eARC to work, both the TV and the soundbar must support it; a link with one ARC-only end runs as ARC. eARC TVs became common from about the 2019–2020 model years. If you are choosing a TV as well, our OLED vs Mini LED guide covers the picture side of that decision.

The workaround for an ARC-only TV: a soundbar with HDMI inputs

If the TV is ARC-only and you own a disc player, Apple TV 4K or console, you do not need a new TV. Many mid-range and higher soundbars have one or more HDMI IN ports. Plug the source into the soundbar, and the bar’s HDMI OUT into the TV. The bar takes the full-quality audio directly and passes the video on; the TV’s ARC limitation never enters the chain.

Check the soundbar’s video passthrough spec before relying on this. Older and cheaper bars pass 4K at 60 Hz with HDR but not 4K at 120 Hz or VRR, which matters for a current game console. If the bar’s passthrough falls short, an HDMI audio extractor with an eARC output is a second route: it sits between source and TV and splits the audio out to the bar.

Check soundbars with HDMI input passthrough on Amazon

DTS: the TV may be the blocker, not the cable

With ARC and eARC the TV is a middleman, and it only forwards formats it is licensed to handle. Samsung’s own support pages state that its TVs do not support DTS, and that includes passing it through to a soundbar. LG left DTS off several model years before bringing it back, and other brands vary by year. Dolby formats do not have this problem in practice.

If you have a disc collection with DTS or DTS-HD soundtracks and a TV that will not pass them, the options are: connect the player directly to the soundbar’s HDMI input, or set the player to decode to PCM — multichannel PCM needs eARC; over ARC you will get stereo.

The TV setting that silently downgrades everything

Buried in the TV’s sound menu is an option called Digital Audio Output, Digital Sound Out, or HDMI audio format. Its choices are usually:

• PCM — the TV decodes everything itself and sends stereo. An Atmos soundbar receiving this will never light its Atmos indicator.
• Auto / Bitstream / Pass-through — the TV forwards the original Dolby or DTS stream to the soundbar. This is what you want.

Many TVs ship set to PCM, or revert to it after a firmware update or after you switch between TV speakers and the soundbar. If a soundbar suddenly sounds flat, check this before anything else. Then check the same setting in the source device: streaming boxes and consoles have their own audio-format menu, and “stereo” or “PCM” there has the same effect. Most Atmos soundbars show the incoming format on their display or in their app — that readout is the quickest way to see what is really arriving.

CEC quirks: one feature, a dozen names

ARC relies on HDMI-CEC for the TV and soundbar to find each other and for the TV remote to control volume. Every brand renames it:

Typical symptoms and fixes:

• The soundbar wakes up at random, or the TV switches inputs on its own. Another CEC device (a console or streaming stick) is sending wake commands. Turn off CEC on that device, or disable its “power on TV” option, rather than disabling CEC on the TV.
• TV remote stops changing soundbar volume. Toggle CEC off and on in the TV menu, then power-cycle both at the wall.
• Sound comes from the TV speakers after every power-on. Make sure the TV’s output is fixed to the HDMI audio system instead of “auto,” and that the soundbar’s auto-power or CEC option is enabled.
• Nothing works after adding a new device. CEC assigns addresses at power-up. Unplug everything for a minute, then power the TV first, the soundbar second, the sources last.

The eARC link has its own discovery mechanism and does not strictly need CEC to pass audio, but remote-control volume still rides on CEC, so in a living room you generally want both on.

Lip-sync: why voices lag and how to fix it

Modern TVs process video heavily — motion smoothing, upscaling, local dimming — which delays the picture by tens of milliseconds. Soundbars add their own processing delay to the audio. When the two do not match, lips and voices drift apart.

• eARC makes automatic lip-sync correction mandatory, so the TV tells the soundbar how long its video pipeline takes and the bar compensates. With ARC the feature is optional and less dependable; with optical it does not exist.
• Manual adjustment: look for AV Sync, Audio Delay or Lip Sync in the soundbar’s app or remote, and sometimes in the TV’s sound menu as well. Adjust in small steps while watching a close-up of someone talking.
• Reduce the cause: Game Mode and turning off motion smoothing shorten the TV’s video delay.
• If only one app drifts, it is the app. Restart it or the streaming device before touching delay settings that are correct for everything else.

Cables: what you need and what you do not

ARC works over any HDMI cable made since HDMI 1.4. For eARC, HDMI Licensing Administrator states that High Speed HDMI Cables with Ethernet and Ultra High Speed HDMI Cables both support it — and nearly every cable sold in the past decade is at least High Speed with Ethernet. A very old or very cheap cable missing that wiring is the exception that produces “eARC not detected.”

If you are buying, get a certified Ultra High Speed cable: the package carries a label with a QR code and hologram you can verify with the HDMI Cable Certification app. There is no audio-quality difference between working digital cables, so there is no reason to pay for exotic ones. Keep the run short — a soundbar sits under the TV, and 3 to 6 feet is plenty.

For optical, any TOSLINK cable works. Remove the tiny plastic caps from both ends (a common first-time miss), push until it clicks, and avoid sharp bends, which crack the fiber.

Check certified Ultra High Speed HDMI cables on Amazon

Check optical TOSLINK audio cables on Amazon

When optical is the right choice

Optical is old, limited and extremely dependable, because it has no handshake and no control channel. Use it when:

• The TV has no ARC port, or its one ARC port is needed for something else.
• CEC is causing chaos you cannot tame, and you would rather control the bar with its own remote.
• The soundbar is a 2.0 or 2.1 model. Stereo and Dolby Digital 5.1 are all it can use, and optical carries both.
• You are diagnosing a fault. If optical gives clean sound and HDMI does not, the problem is the ARC handshake, the cable or a setting, not the soundbar’s amplifier or speakers.

The costs: no Atmos or Dolby Digital Plus, and no volume control from the TV remote unless the soundbar can learn infrared codes — most can; look for “IR learning” in its manual. Set the TV’s digital output to Dolby Digital or Auto instead of PCM to get 5.1 rather than stereo.

Check 2.1 soundbars with HDMI ARC and optical on Amazon

Where this article stops

This guide covers a TV and one soundbar. It does not cover AV receivers with multi-zone setups, wireless rear-speaker pairing, or a TV that shows no picture at all, which is a different handshake problem from the one here. Format support on a specific TV or soundbar changes with model year and firmware, and the only authoritative source is that model’s manual or spec page; we have not tested individual models. Figures quoted here come from HDMI Licensing Administrator and manufacturers’ support documentation.

Summary

Use the TV’s ARC/eARC port and the soundbar’s HDMI OUT, turn on CEC, and set the TV’s digital audio output to Auto or Pass-through instead of PCM — that setting causes more flat-sounding soundbars than any cable does. Plain ARC carries Dolby Digital Plus, which is how every major streaming service delivers Atmos, so eARC’s 37 Mbps only earns its keep with lossless TrueHD or DTS-HD from discs and with Apple TV 4K or Xbox Atmos. On an ARC-only TV, a soundbar with HDMI inputs sidesteps the limit. Optical carries stereo and 5.1 Dolby Digital or DTS and nothing newer, but it has no handshake to fail, which keeps it useful as a fallback and a diagnostic.

More home theater and gadget guides at GadgetHub English.

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