Quick answer: HDMI audio out comes from three places: the ARC or eARC return channel, an extractor box that splits audio from an input stream, or the source menu itself. The format you receive is decided by the EDID the sink reports. If the display advertises stereo only, the source will downmix before the extractor ever sees the stream.
A customer connects an extractor, sets the TV to bitstream, and still gets two channel audio. Nothing is broken. The source read an EDID that described a stereo display, so it downmixed before transmission, and the extractor faithfully passed the result. Understanding that order of operations saves hours of swapping boxes, and it explains why the same extractor works in one room and not in another with a different television.
The three legitimate audio paths
ARC sends audio backwards down the same HDMI cable that carries video to the display. eARC adds bandwidth and a dedicated data channel, so it can carry lossless formats. An extractor sits between source and display, reads the stream, and outputs audio over TOSLINK, coaxial RCA or analog while passing video through. The source menu option is the simplest path when the player has a second output or a built in app that can send audio elsewhere.
Each path has a different failure mode. ARC depends on CEC and on both ends agreeing about the return channel. An extractor depends on EDID management and on its own ability to pass high bandwidth video untouched. The source menu depends on the app supporting the format at all.
How EDID decides what you hear
The sink describes itself first
When the link starts, the display returns an EDID block listing supported resolutions and audio formats. The source then chooses a format both ends accept. A television that reports two channel PCM forces a downmix at the source. An extractor placed between them can present its own EDID, claiming support for Dolby Digital or multichannel PCM, which is how it recovers surround that the display would otherwise refuse.
Downmix happens before the cable
Once the source has downmixed, no downstream device can rebuild the missing channels. This is the single most common misunderstanding in HDMI audio troubleshooting, and it is why the extractor must sit where it can influence the handshake rather than after a splitter that already answered for the display.
Choosing between an extractor and ARC
| Path | Best for | Limit | Typical symptom |
|---|
| ARC | TV apps to soundbar, one cable | Compressed 5.1 only | No sound after input change |
| eARC | Lossless audio, object formats | Both ends must support it | Falls back to ARC silently |
| Extractor | Legacy AV receiver, analog amp | Needs EDID control | Stereo only, or no video |
| Source menu | Player with dual outputs | App dependent | Format greyed out |
What actually breaks in the field
CEC fights between devices
ARC rides on the CEC bus, and CEC implementations differ enough that one device can steal the audio path or wake the wrong input. Disabling CEC on the display and using an extractor is often more stable than debugging the bus.
Video passthrough that is not transparent
A cheap extractor may strip HDR metadata, force a lower colour depth or refuse 4K120. Check that the box declares the same video capability as the display, otherwise the picture degrades to fix an audio problem.
Power sequencing after standby
Extractors that lose power with the display can leave the source holding a stale EDID. A cold boot of all three devices usually restores audio, which points to the sequencing rather than the cable.
Practical scenarios
- Soundbar with one HDMI port: connect the source to the soundbar input and pass video to the display, so the bar answers the handshake with full audio support.
- Old analog amplifier: use an extractor with analog output and set the source to PCM, since the amplifier has no decoder.
- Projector without ARC: an extractor at the projector end feeds a receiver, and the projector only sees video.
- Console plus capture card: put the extractor before the capture device so the card sees the same video the display does.
FAQ
Why does my extractor output stereo only?
The EDID it presents probably claims stereo, or the source downmixed before the extractor. Check the source audio setting first.
Can ARC and an extractor be used together?
They can, but the handshakes may conflict. Choose one audio path and disable the other in the display menu.
Does HDMI audio out support 5.1 over TOSLINK?
TOSLINK carries compressed 5.1, not lossless. If the source sends lossless, the extractor must downmix or the format will not pass.
Next step
Decide the audio path before buying hardware, because the EDID behaviour follows from it. The eARC and ARC guide covers the return channel in detail, the coaxial S/PDIF guide explains the digital output most extractors provide, and the HDMI distance guide keeps the video side of the chain inside its limits.
