Watch the Affordable Shuffle Solo online guitar lesson by Jeff McErlain from Essentials: Advanced Blues Soloing
I would say this is the most difficult solo in this course for a number of reasons - the overall feel, triplet slurs, and of course, the quick diminished lick. Let's discuss the diminished scale, as everything else is a mixture of the major and minor pentatonic scales. The diminished scale is symmetrical, often referred to as the symmetrical diminished scale! The scale formula is half step - whole step - half step - whole step, etc. It's an eight-note scale, and the theory behind it can get pretty deep, so here we're just sticking our toe into the pool.
The typical spot where Robben uses the scale is the change from the I7 to the IV7 chord in the blues. This occurs on Bar 4 as a change to the iV7, which occurs on Bar 5. The simple explanation as to what is going on is that we're adding some tension before the change in resolving to a chord tone on the downbeat of Bar 5. I would suggest playing the lick and looping it, as you can use the Soundslice function. Please take advantage of that tool, it's fantastic!