The Arc has no HDMI input of its own, so your TV is always in the middle: the source sends Atmos, the TV passes it over (e)ARC, and the Arc decodes it. When Atmos doesn't play, the break is almost always at the TV — and the single most common cause is the TV's digital audio output being set to PCM. So before changing anything, find out what the Arc is actually getting. (If the Arc is silent entirely rather than just missing Atmos, start with Sonos Arc no sound from the TV instead.)
First, check what the Arc is receiving
In the Sonos app: System > System Settings > About My System, scroll to the Sonos Arc, and read the "Audio In:" line. It tells you exactly where you stand:
- "Dolby Atmos" or "Dolby Atmos (Dolby TrueHD)" → it's working; you're done.
- "Dolby Digital" → the TV is passing compressed audio but not Atmos — fix passthrough.
- "Stereo PCM" or "Multichannel PCM" → the TV is decoding to PCM instead of passing the bitstream. This is the #1 cause.
(Quicker glance: the Now Playing screen shows the Dolby Atmos logo on a real Atmos signal.)
Fix it
- Set the TV's digital audio output to Pass-Through / Bitstream / Auto — not PCM. PCM strips Atmos. This one setting fixes most cases.
- Enable eARC and use the eARC port with a certified Ultra High Speed cable. Plain ARC can carry lossy Atmos (via Dolby Digital Plus) but never the lossless TrueHD kind; eARC carries both — see ARC vs eARC differences if you're unsure which port you're on.
- Make sure the source actually outputs Atmos. Built-in TV apps send Dolby Digital Plus Atmos (works over ARC/eARC). An Apple TV 4K sends Atmos in a format that requires eARC — with eARC off it drops to stereo PCM. A 4K Blu-ray's TrueHD Atmos needs eARC plus a TrueHD-capable source.
TV-brand settings that trip people up
The menu names differ, but the idea is identical — enable eARC and set output to passthrough:
- Samsung: Sound > Expert Settings → HDMI-eARC Mode: Auto, Digital Output Audio Format: Pass-Through; turn on Anynet+.
- LG: Sound > Advanced → eARC On, Digital Sound Out: Pass Through (some models need Auto to avoid Netflix/Disney+ dropouts).
- Sony Bravia: enable Passthrough + eARC. Note some Bravias don't support Atmos passthrough at all — that's model-dependent, not a setting you can force.
FAQ
The app says "Stereo PCM" — what's wrong? The TV is decoding to PCM instead of passing the bitstream. Set its digital audio output to Pass-Through/Bitstream and it'll switch to Dolby.
Do I need eARC, or is ARC enough? ARC can do lossy Atmos (Dolby Digital Plus) only. For lossless TrueHD Atmos from discs — and for the Apple TV 4K's Atmos at all — you need eARC.
Atmos works from Netflix but not my Apple TV. The Apple TV's Atmos needs eARC. Built-in apps use a format that survives plain ARC; the Apple TV doesn't. Enable eARC on the right port.
How do I confirm it's actually Atmos? Check About My System → Audio In, or look for the Atmos logo on the Now Playing screen. Don't trust the source app's label alone.