Originally Posted by PhilipOneL
Are AAC+ and xHE-AAC synonyms?
No. AAC (Advance Audio Coding) is one of the audio coding format standards.
Very simply, HE-AAC (High Efficiency Advance Audio Coding) is an upgrade to AAC. This is sometimes termed AAC+.
xHE-AAC (extended High Efficiency Advanced Audio Coding) combines HE-AAC with MPEG-D.
There are may references on the web, here is one: