Watch the Steady Top Note online guitar lesson by Brad Carlton from Chord Studies: Slow Blues Progressions Vol. 1
This is a slow blues in the key of F. Notice how the chords are voiced: you'll notice the top note of each chord frequently is the same note and also the use of those 9 sus 4 chords to give the progression an airy and modern sound. Take a look at the fourth chord in the progression: this chord is an Ab with a sixth and a seventh note in the bass. Slashes are used to denote when a tone other than the root is in the bass of the chord.