Watch the Level 3: Blues Chord Melody online guitar lesson by Jason Loughlin from Take 5: Blues Chord Melody
In this etude, we'll be adding augmented and diminished chords. We can add these to the chords in our progression or to any of the IV/I, IV/IV, V/I or V/V's to get an altered sound. An altered chord means that has either the 5th, 9th or 11th lowered or raised a half-step. An augmented sound can be adding to any chord acting as a dominant to the chord following. Most commonly it's used on the I chord leading into the IV or the V chord leading back into the I.
The diminished shape is a little trickier to use. It's primarily used to access the b9th of a chord. The easiest way to apply it is to build it off of the note a half-step higher than the root of the chord, the 3rd, the 5th or b7th. If you were playing over an A7, you could build it off of Bb, C#, E or G. This would lead nice into a D7.