please notice the additional signals...how come?
(http://t.imgbox.com/accFzQyH.jpg) (http://imgbox.com/accFzQyH) (http://t.imgbox.com/adtE3wTt.jpg) (http://imgbox.com/adtE3wTt)
“encoded” with what?
As for why, lossy encoding changes signals and can add distortion; I would have hoped that was obvious. Please also now notice that the added components are below –110 dB, and it is highly unlikely that you could hear them, even on their own but especially with normal signals superimposed over them.