Key takeaways
- Optical physically cannot carry Atmos or DTS:X even when the new soundbar is fully capable, since it tops out at Dolby Digital 5.1 and DTS 5.1.
- Leaving a TV set to PCM instead of bitstream quietly strips Atmos and DTS:X metadata even over an eARC connection that is otherwise fully capable of carrying it.
- Only one HDMI port on a modern TV actually carries the return audio channel a soundbar needs, and using a different one leaves that channel unavailable regardless of cable quality.
- An HDMI switch bought before ARC and eARC existed has no path for a return audio signal at all, and removing it is usually the actual fix rather than troubleshooting around it.
- Firmware updates regularly patch specific eARC handshake bugs between brand combinations, so a setup that worked for months can start failing after only one side updates itself.
The soundbar shows an Atmos logo on its display, but the sound underneath is plain stereo or 5.1 at best. That is one of the most common complaints behind a home theater service call, and it almost always traces back to one of five habits formed while connecting the gear, not a fault in the bar itself.
Mistake 1: The old optical cable never got replaced
Upgrading to an Atmos soundbar and reusing the optical cable already run behind the TV feels efficient. It is already in place, it already carries sound, and the new bar makes noise the moment it is plugged in, so nothing seems wrong at first.
What it costs: optical, also known as TOSLINK, has no bandwidth for object based metadata and tops out at Dolby Digital 5.1 and DTS 5.1, both compressed formats. Atmos and DTS:X simply cannot travel down that cable, no matter how capable the soundbar plugged into the other end is.
A customer called convinced the new bar itself was faulty, since the box promised Atmos and the living room got plain stereo instead. The old optical cable, still taped along the skirting board from a system bought eight years earlier, was the entire explanation. Nothing about the bar needed fixing at all.
The fix is a single cable swap: connect through the TV’s HDMI ARC or eARC port instead. The full difference between optical and HDMI for TV audio covers what each connection can and cannot carry, including why ARC alone is enough for most streaming Atmos. The Dolby technology overview explains why that object based metadata needs a connection with real bandwidth behind it in the first place.
Mistake 2: The TV’s audio output stayed on PCM
PCM is the default digital audio setting on plenty of televisions straight out of the box, buried in a menu most people open once during setup and never again. Sound plays fine, so the setting never gets a second look.
What it costs: PCM means the television has already decoded the audio itself before sending it onward, which strips the object based metadata Atmos and DTS:X depend on even when the HDMI connection is otherwise fully capable of carrying it. The soundbar ends up receiving plain channels instead of objects.
The fix is one setting change: bitstream, sometimes labelled passthrough, instead of PCM, whenever a soundbar or receiver is doing the decoding rather than the TV itself. Which setting suits which setup covers the small number of cases where PCM is actually correct, mainly a TV with no external audio device attached at all.
Confirming the change actually stuck matters as much as making it. The soundbar’s own display or app should show a format readout, Dolby Digital Plus or Dolby TrueHD rather than plain PCM, during a title already known to carry Atmos. If it still reads PCM after the setting was changed, the setting did not save, or a second app specific audio option on the TV is quietly overriding it.
Mistake 3: The cable is in an HDMI input, not the ARC port
Most televisions carry three or four HDMI inputs that all look identical from the back panel. Plugging into whichever one happens to be free, rather than the one specifically labelled ARC or eARC, feels like it should not matter.
What it costs: silence, or audio that only works for some apps and not others. Only one HDMI port on the television carries the return audio channel a soundbar depends on, and using a different one leaves that channel unavailable no matter how new or expensive the cable itself is.
The fix takes under five minutes: check the TV’s own manual for the exact port number marked ARC or eARC, since on screen labelling is often missing or too small to read behind the set. Finding and confirming the correct port walks through this by brand.
One install had two HDMI inputs sitting side by side on the back of the TV, identically shaped, with a label printed in grey text on a black panel that was unreadable without a torch. The soundbar had been in the wrong one for three weeks before anyone noticed, since the picture worked perfectly the entire time and only the audio quietly stayed at plain stereo.
Mistake 4: An old HDMI switch is still in the chain
A switch box bought years ago to add extra HDMI inputs to an older TV often survives every upgrade since, quietly sitting between the new soundbar and the rest of the rack because it still physically works.
What it costs: a switch built before ARC and eARC existed has no path for the return audio channel to travel through at all, and one built before HDMI 2.1 caps bandwidth well below the 48 Gbps a modern Atmos and 4K120 signal needs. Whether the soundbar or the TV should be the hub is worth settling before adding any switch back into the chain.
An HDMI switch that predates eARC will not pass a return audio signal through at all, even if every other cable and setting is correct. Removing it entirely, rather than troubleshooting around it, is usually the actual fix.
The fix is removing the switch from the audio path specifically, even if it stays in place for video only, or replacing it with one explicitly rated for eARC and HDMI 2.1 bandwidth. A switch bought around 2015, built to HDMI 1.4’s roughly 10 Gbps ceiling, cannot carry a modern eARC signal at all, and no amount of reseating cables changes that fact.
Mistake 5: Firmware updates keep getting postponed
A soundbar that already works gets left alone. Firmware update prompts get dismissed on both the TV and the bar, sometimes for months, because nothing appears broken yet.
What it costs: manufacturers regularly patch specific eARC handshake bugs between brand combinations, and a working setup can start dropping Atmos or falling back to stereo after one side, the TV or the bar, updates itself automatically while the other stays on old firmware. What firmware updates actually fix, and what they occasionally break covers both sides of that trade.
A customer’s new receiver kept losing Atmos every few weeks for no obvious reason, and the pattern only became clear once the TV’s own update log was checked: three separate automatic updates in two months, each one resetting the digital audio output back to a default the receiver did not expect. The fix was checking that single setting after every update rather than assuming it would hold.
| Connection | Carries Atmos | Common mistake |
|---|---|---|
| Optical | No, tops out at 5.1 | Reused from the old system out of habit |
| HDMI ARC | Streaming Atmos only | TV left on PCM instead of bitstream |
| HDMI eARC | Streaming and disc based | Cable plugged into the wrong HDMI input |
All five mistakes share the same shape: nothing on the surface looks broken, sound still plays, and the fix is a single cable, a single menu setting, or a single update check rather than a return or a new purchase. None of them require buying anything new, which is exactly why they go unnoticed for so long.
- Confirm the TV connects to the soundbar over HDMI ARC or eARC, not optical
- Set the TV’s digital audio output to bitstream or passthrough
- Verify the cable is in the port actually labelled ARC or eARC
- Remove any HDMI switch that predates eARC from the audio path
- Check both TV and soundbar firmware every few months, not only when something breaks
Questions readers ask about this
Not necessarily. A lit Atmos logo means object based data is arriving, so a thin sound is more likely a calibration or speaker placement issue than a connection fault. Check the connection first to rule it out, then look at level settings and up-firing speaker placement if the logo is genuinely on.
Yes, most soundbars accept both physically, though only one input is active at a time, chosen in the bar's own input menu. It causes no harm and no benefit beyond convenience, since the active connection still needs to be HDMI ARC or eARC for Atmos to work at all.
Check the switch's own specification sheet for ARC or eARC support directly. Most switches sold before around 2016 predate both entirely, and the symptom is a total absence of return audio regardless of what the TV's own settings say, since the switch has no signal path for it.
Installing it within a week or two is generally sensible, particularly after adding a new source device to the rack. Waiting slightly to check for release notes mentioning known issues is reasonable, but leaving updates dismissed for months is what actually causes most of these mistakes.
Yes, on the small number of setups where the TV itself is doing all the decoding and the soundbar is only reproducing already decoded audio rather than receiving a raw bitstream. That arrangement is uncommon with a modern Atmos capable soundbar, which is normally the device doing the decoding.
About the author
Rahul Gupta
Rahul Gupta has spent nearly a decade quietly wiring living rooms, testing soundbars in every awkward apartment layout imaginable, and untangling the kind of HDMI handshake problems that make people give up on Atmos altogether. He writes here about what actually works when you get the boxes home—not what the spec sheet promises. If a piece of gear on this site earns a recommendation, it earned it in a real room with real furniture, not a lab.
