So what it boils down to was Elvis produced his own records. He came to the session, picked the songs, and if something in the arrangement was changed, he was the one to change it. Everything was worked out spontaneously. Nothing was really rehearsed. Many of the important decisions normally made previous to a recording session were made during the session. What it was was a look to the future. Today everybody makes records this way. Back then Elvis was the only one. He was the forerunner of everything that's record production these days. Consciously or unconsciously, everyone imitated him. People started doing what Elvis did.
Bones Howe. recording engineer, as quoted in Elvis, A Biography (1971) by Jerry Hopkins.