Rodney Jerkins spoke about the sound of the 'Invincible' album, and he strongly implied that the album would have sounded cleaner if they used Pro Tools (which is a digital way of recording), instead of using Analog (which is a analog way of recording).
But Michael Jackson insisted on using Analog, because he was not only uncomfortable with Pro Tools but also he was a little scared of this technique.
"I like digital because it's a lot cleaner, but I love the warmth of Analog. Sometimes I use both. We record everything in Pro Tools. The last time I used Analog was on Michael Jackson in 2000. He was a little scared of Pro Tools. We tried to get him to use it, but he didn't want to go that route yet and I understand: He came from the school of Analog" (Rodney Jerkins, Mixonline.com)
Also, many fans want the 'Invincible' album to be produced and mixed again but using this time real musical instruments because they like the sound of the 'Threatened' song (with real musical instruments) that is played in the 'This Is It' film.