Watch the Freddie Free online guitar lesson by Chris Buono from Guitar Lab: Blues Progressions
In Freddie Free we free ourselves of the #ivdim7 chord and go down another additive-chord road that's completely different. Playing a seemingly straight laced 12-bar blues in Bb, everything seems standard-blues-progression copacetic until bar 11 where a bVII7 (Ab7) gets dropped. This hip approach is inspired by the work of jazz luminary Miles Davis and his forward-thinking composition entitled "Freddie Freeloader". The shift and surprise this chord brings is very effective and actually sounds smooth as butter even in simple voice leading scenarios. This is partly due to the fact you're moving a 4th below (or 5th above) from the IV chord (Eb7) in bar 10, which is a movement that's strewn about the blues and is extremely stable.
Freddie Free also gets you hip to the idea of mixing concepts. Taking some ideas from Larry's Trick with complementary m7 chords bouncing off the primary changes, this time they are played after the primary chord. In the third chorus the idea is taken to new levels where the primary chords are subbed out to m7b5 chords built off the 3rd and the bouncing m7s are built from the 6th.