Optical Audio Adaptor, how does it work?

  • 23 March 2024
  • 8 replies

Ok, I have to plead optical audio ignorance here, but how does the Optical Audio Adaptor (came with the ARC sound bar) work?  

How does the adaptor convert the optical audio out signal from the TV to an HDMI signal?  There is no electronics to convert from optical audio to HDMI built into this thing that I can see!

The reason I asked is because I assumed that I could simply plug the optical audio adaptor into to my LG TV’s optical audio out plug (as it should be), set the tv to optical output and the connect adaptor via HDMI cable to one of the HDMI plugs on a Pioneer receiver and I’d get audio.  Apparently it doesn’t work that way!  

What am I missing?  

Any input would be appreciated and thanks in advance.



8 replies

Userlevel 7
Badge +23

It is likely a Sonos-only device.

HDMI-ARC doesn’t use most of the wires in the HDMI plug. My guess is that this adapter takes optical and converts the signal to digital then sticks it on a couple of pins. The Arc/Beam’s hdmi port likely has some magic to recognize the adapter and knows how to take the “digital optical” signal.

A “real” hmdi signal, that you’re receiver is expecting, require an awful lot more signal (like video!) to work.

I’m pretty sure that adapter only works with Sonos devices.

Can we assume it at least draws power from the HDMI that it is attached to so that it can do this transformation of data? Hmmm. I need to go read up again on the HDMI spec, it’s been years. 

It’s hard to believe it’s totally passive, but then I’m not an expert here, I have insignificant knowledge.

Userlevel 7
Badge +22

Answer may be in even more detail here, I don’t want to wade through all of it though.



“Therefore the adapter gets power from soundbar HDMI connector and it has a TOSLINK input to receive optical S/PDIF digital audio stream from the TV. The same S/PDIF stream is then sent to the soundbar over the UTIL pin in HDMI connector almost as if it were a coaxial S/PDIF signal, the electrical specs are only slightly different.”

There are two audio paths on an HDMI cable — to and from. On a regular HDMI connection audio from a source (DVD  player, cable box, AppleTV, etc.) will go directly to a TV. However, most modern TV’s can also be their own source for online content. This requires an “audio return” path from the TV back to the A/V receiver that is handling audio for the TV. The audio return path uses a separate set of pins in the HDMI cable and a processor at both ends of the cable must be aware of this. SONOS soundbars use the return audio path or an optical connection that knows nothing about the HDMI drama. The SONOS HDMI to optical converter routes the return audio to the optical connection.

HDMI sockets can provide a limited amount of power to a client device.

Ok, I appreciate every ones input & think my question has been answered.  The Sonos optical audio to hdmi adaptor will not do what I want and that was just to get the tv audio down to a receiver used driver outside speakers.  Back to the drawing board.  Thanks again.

Userlevel 7
Badge +22

The TV’s TOS / optical connection is likely your best bet and the most versatile option.

Yes, I’m going to buy an optical cable and give that a try.  I was just trying to do this with unused cables I already have laying around.  Thank you.