That is only Drop D. It simply changes what you play on the low E string. You can pretty much play the song either way with very little difference, but it is 'better' in drop D (for the droning low D at one specific point after/during the solo ------------ "Did you ever really need somebody, really need them bad..."

Remember that he would often use slightly different tunings when playing some of the songs live (ex. Bron-Y-Aur Stomp live he would play in open G rather than F, but for the most part these were simply key changes) Also, I have no idea if he stayed in the same tuning for When the Levee Breaks on 'No Quarter.' (playing on the Ovation 12-string). Hard to tell.