Robben Ford has spent his career carving out a musical buffer between blues, rock and jazz/fusion. That could be a recipe for slick blandness, but Robben creates something wonderful, combining the best elements of his diverse influences.
One of the best-known aspects of his playing is the diminished scale, which "seems to loom large in my legend", as he jokes. In these examples, we'll work through the concepts that Robben discusses on the video, showing how the diminished scale is closely bound up with the old 12-bar blues progression.
First of all, the technical stuff. The diminished scale has eight notes, with alternating semitone and whole tone intervals. You can start with either interval, but the more common half-whole variety is applicable to what we're doing here. Here it is in G.
Ex1 tab (right-click to download)
It's a strange scale, but it works nicely over a (jazzy) blues in G because it contains so many tasty notes. The b9th (Ab), #9th (A#) and 13th (E) are common extensions added to the G7 chord, and then the C# (or Db) is the tritone, a vital bluesy sound!
Ex2 tab (right-click to download)
Feel free to jam with the scale, but here's what Robben shows us on the video. The B note in the G diminished scale becomes a moment of tension as we await the imminent C7 chord. Moving chromatically to the C note takes us out of the diminished scale, but the urge to resolve to the root note of C7 is more powerful.
Ex3 tab (right-click to download)
Using Bb13 as a passing chord, Robben creates this cool chord-melody change from G to C. Strictly speaking, a 13 chord should also include the 9th, but by omitting it, all of the notes from G13 and Bb13 are within the G diminished scale. Clever!
Ex4 tab (right-click to download)
Robben prefers not to use this trick with C diminished (C Db D# E F# G A Bb) for the C7-G7 (IV-I) change. There's certainly a different shape to it, without that chromatic resolution. However, he uses it later in the blues progression, for the D7-G7 (V-I) change.
Ex5 tab (right-click to download)
People often confuse the diminished scale with the diminished 7th arpeggio, which is basically a stack of minor 3rd intervals (Gdim7 is G Bb Db E). That's not so daft, though; the diminished scale contains two interlocking dim7 arpeggios, Gdim7 and Abdim7 in this case.
Ex6 tab (right-click to download)
And the upshot of that is that every note in the scale is a minor 3rd (three frets) from another scale note. Therefore, any diminished scale phrases or lick can be moved up or down three frets and you'll still be within the scale.
Ex7 tab (right-click to download)