HDMI eARC and HDMI 2.1, Explained

ARC and eARC send audio backwards down an HDMI cable — from the television to the receiver, rather than the usual direction. That is what lets a television’s built-in apps play through your speakers without a second cable.

The upgrade from ARC to eARC is about how much audio can travel that path, and HDMI publishes the answer.

What eARC is specified to carry

From HDMI’s own specification page, eARC:

“supports the latest high-bitrate audio formats up to 192kHz, 24-bit, and uncompressed 5.1 and 7.1, and 32-channel uncompressed audio. It also supports DTS-HD Master Audio, DTS:X, Dolby TrueHD, Dolby Atmos.”

Those four format names are the point. TrueHD and DTS-HD Master Audio are lossless soundtrack formats; Dolby Atmos on Blu-ray rides on top of TrueHD. They are the formats the older ARC connection and an optical cable cannot carry.

The part almost nobody checks: only one port is the eARC port

eARC lives on the HDMI output, not on the inputs. On the receivers we cover:

So the cable that carries audio back from your television has to be plugged into that specific socket, and the television’s HDMI port has to be its eARC port too. Both ends have to support it. This is the single most common reason an eARC connection silently falls back to plain ARC.

The finding: an 8K receiver is 8K on some inputs

This is the part that costs people money, and every manufacturer publishes it plainly enough — in a footnote.

Three receivers, three manufacturers, and all three give you exactly three HDMI 2.1 inputs. If you own a PlayStation 5, an Xbox Series X and a 4K Blu-ray player, you have filled them. Add a fourth device that wants 4K/120 and it goes on a 2.0 port, where it will run at 4K/60.

Onkyo is the clearest about it, publishing input numbers with the split stated. Onkyo’s three HDMI 2.1 inputs are also the reason it is the pick on this page for anyone with consoles — it is not more 2.1 ports than the others, it is the same three, published unambiguously.

The other HDMI 2.1 features, and which receivers publish them

The video features that travel with HDMI 2.1 matter to gaming more than to film.

• VRR— variable refresh rate, so the display matches the console’s frame output rather than tearing or stuttering.
• ALLM — auto low latency mode, which switches the television into game mode automatically.
• QFT — quick frame transport, which reduces latency by sending each frame faster.

Denon publishes VRR, QFT and ALLM for the AVR-X1800H along with 8K/60 Hz and 4K/120 Hz passthrough. Yamaha publishes 8K/60 and 4K/120 for the RX-V4A. Onkyo publishes HDMI 2.1 at 8K/60 and 4K/120 on inputs 1–3 and both outputs.

If you have no console, none of this changes anything about how a film sounds or looks.

When you still need optical, and when you should not use it

Optical remains genuinely useful in two situations: connecting an older device that has no HDMI audio output, and breaking a ground loop, because an optical link makes no electrical connection between the boxes at all.

It is the wrong choice when the formats matter. Every device we cover states its optical limits explicitly — WiiM publishes “stereo PCM only” for the Pro Plus’s optical input, with Dolby Digital and DTS unsupported; Denon publishes linear PCM for the PMA-600NE’s optical and coaxial inputs. The comparison is worked through in optical vs coaxial vs USB.

There is a middle case worth knowing about. The WiiM Ultra publishes an HDMI ARC input accepting PCM and Dolby Digital 5.1, while the WiiM Amp publishes HDMI ARC as stereo PCM only with Dolby Digital and DTS not supported. Same connector, same brand, different capability — which is exactly why the format list matters more than the socket name.

Who decodes, and why it changes what you should set

There are two ways audio can travel from a source to your receiver, and the setting that chooses between them is buried in every device’s audio menu.

Bitstream sends the undecoded soundtrack and the receiver decodes it. This is what you want for Dolby Atmos and DTS:X, because the receiver is the box that knows how many speakers you have and where they are.

PCM means the source decodes it and sends the finished channels. The receiver then has less to do — and on some devices, less it is able to do, because object-based formats like Atmos have already been rendered to a fixed channel layout before they arrive.

The practical rule: set the source to bitstream when the receiver supports the format, and to PCM when it does not. That second case is common. Denon’s own info sheet for the AVR-S670H lists no Atmos and no DTS:X — Dolby TrueHD, Digital Plus and Pro Logic II only — while Denon’s product page title for the same model says “with Dolby Atmos”. We publish both, and we lean on the spec table. If Atmos is the reason you are buying, verify before you do.

Bass management still happens after eARC

Getting a lossless soundtrack into the receiver is only the first half. What the receiver then does with it is decided by the settings the calibration routine writes — speaker sizes, crossover frequencies, distances and levels.

It is worth saying because the two get confused. eARC is a transport question: can the audio physically get here. Bass management is a routing question: where does each frequency go once it has. A perfect eARC connection into a receiver that thinks your bookshelf speakers are “large” will still send them bass they cannot produce, and the subwoofer will sit idle.

Check the speaker sizes and crossovers after any change to the connection, not just after a speaker change.

Cables

For 8K/60 or 4K/120 you need a cable certified for the bandwidth. For eARC audio alone, an existing high-speed HDMI cable is normally fine, because eARC’s audio payload is a small fraction of a video signal’s.

We do not have a cable specification we can compare and rank, so we are not recommending one. Buy a certified cable of the right category and stop there.

The practical checklist

1. Television to receiver:the television’s eARC port to the receiver’s HDMI output. Not an input.
2. Both ends must support eARC, not just the receiver. If either is ARC-only, you have ARC.
3. Enable it. On most televisions eARC is a menu setting, often alongside a CEC control that has to be on as well.
4. Put your 4K/120 sources on inputs 1–3 and everything else on the rest. The 2.1 inputs are a subset on every receiver we cover.
5. If a soundtrack format is missing, check the television’s output setting before assuming the receiver is at fault.