The places where Elvis Presley and his band once stood while recording hits at fabled Sun Studio in Memphis, Tennessee have been marked with crosses on the studio floor - because those were the spots perfectionist producer Sam Phillips considered the best for sound.
Now, anyone recording at the music mecca is advised to use the crosses to get the optimum quality when recording tracks.
Producer T Bone Burnett recently discovered the Sun Studio secret while working on John Mellencamp's new album.
He tells Rolling Stone magazine, "Sam walked around that room and found where every instrument sounded best."
But the in-demand producer warns others heading to Sun Studio to be prepared for a spooky experience: "It has ghosts."