I'm looking at the small Sonos optical audio (toslink) -> HDMI cable in front of me and I don't know how it works (https://www.sonos.com/en/shop/optical-audio-adaptor.html). It has an optical audio input and can be connected to a speaker via HDMI, so basically it looks like it converts the optical signal.
I can only find clunky HDMI audio splitters that also output optical, but I don't know how this cable works since it is so small – or is it and this is totally normal?
How do optical -> HDMI cables / splitter work anyways? Is there a small IR diode in there detecting optical signals directly converting them? Is there a small contraption inside this cable?
Best Answer
That adapter is meant to be used with a soundbar that can only receive audio from a television via HDMI Audio Return Channel (ARC) connection.
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.
So the adapter does not need to handle HDMI streams at all. However it might have a specialized chip for the ARC physical interface to meet the electrical specs of the S/PDIF signal.