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. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.