In this video
Acoustic Loop - D Backing Track
We learn a melancholic jam in the key of D major.
Theory points
Chords in the key of D major are; D, Em, F#m, G, A and Bm.
This example also uses a G minor chord, which is the minor IV chord in this key. This is a common trick when going from IV (major 4 chord, iv (the minor 4 chord) and I (one chord, i.e. key of the song).
The minor IV chord works so well because of the descending chromatic movement between the chord tones. The third of the IV major chord moves down a half-step to the third of the minor iv chord which moves down to the fifth of the I chord.
Strumming Pattern
Lead Line
This chromatic movement from the chords in echoed in the lead line. The lead is built upon a descending melodic line played on string 3 only and mainly uses notes only from the chord it is played over.
The G minor chord in this progression is out of key and therefore we should match our lead notes with the chord we are playing over. This moves us beyond using one scale for an entire song or jam, using a technique known as following the chord.
See all chord diagrams below. Blue notes = chord tones, Orange notes = string 3 descending chromatic
Chord 1 - D7
Chord 2 - G major/ D
Chord 3 - G minor/ D
Chord 4 - D major
Full example - Interactive tab