Hi. This may sound like a daft question but do TV channels broadcast in more than one format?
What I mean is before I had the Sonos Arc I had no idea what format I was playing as I had no way of knowing.
Then before I had added the Sonos Sub Gen 3, the Sonos app was showing as, say, Stereo PCM and finally now that I have added 2 surround speakers it is showing as Dolby Digital 5.1
So surely the same broadcast must be broadcasting audio in multi-formats at any one time? 
There is communication between your Arc, TV, and whatever source is playing about what audio quality your system is capable of playing, to give you the best quality audio. Same thing happens when it comes to video quality. TV channels, streaming sources, game consoles, physical media, etc generally do come in multiple formats so that you get the best quality that your particular setup can handle. Obviously, some content isn’t created in all formats, and therefore, you won’t get the best quality every time, or content isn’t capable of playing on your system (although stereo is generally the default).
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