In my last post I explained the structure of suspended fourth (sus4) chords. Now I would like to say a few words about improvising over these chords. By 'static', I mean sus4 chords that do not resolve to another chord (usually a fifth below). These static chords are used in a modal way with no need to resolve. As I mentioned in my last post, a great example for such static sus4 chords is Herbie Hancock's composition Maiden Voyage.
I would like to focus on pentatonic scales because they sound great over suspended chords, and most guitar players already know them. As you probably know, the most common pentatonic scales are the minor and the major pentatonic scales:
A minor pentatonic scale: a - c - d - e - g
C major pentatonic scale: c - d - e - g - a
These two scales are of course identical, they just have different roots. Let's have a look at the notes of a 7sus4 chord with added tensions 9 and 13, e.g. with root D:
D13sus4 = Am9/D = d - g - a - c - e - b
(If you have trouble understanding this, just check my previous post).
If you compare these notes to the notes of the A minor pentatonic scale, you'll notice that the scale contains all chords tones except for the 'b'. That makes this scale is a great choice for improvising over a D13sus4 chord (and over all other D7sus4 chords with or without added tensions). If you want to use a scale that also contains the 'b' (which is the '13' of the chord), then you'll have to exchange this note for another chord tone if you want to stick to pentatonic scales (because they only contain five notes, whereas the D13sus4 chord has six notes). The E minor pentatonic scale adds the 'b' at the expense of the 'c':
E minor pentatonic scale: e - g - a - b - d
Listen to the next two sound samples to hear how those two scales sound over a D13sus4 chord:
A minor pentatonic scale over D13sus4:
E minor pentatonic scale over D13sus4:
I hope you agree that they both sound good.
Let's summarize: if you want to play pentatonic lines over a suspended fourth chord (e.g. D7sus4, D9sus4, D13sus4), use a minor pentatonic scale with the root either a perfect fourth below or a major second above the root of the chord. Over a D7sus4, this gives A minor and E minor pentatonic, respectively.
I'd recommend to you to use this pentatonic approach to improvise over Maiden Voyage by Herbie Hancock. The song starts with 4 bars of D13sus4 (Am9/D) followed by 4 bars of F13sus4 (Cm9/F). These 8 bars are then repeated. For a start, just use these 16 bars for playing some pentatonic lines. So what are the scales? As mentioned before, over D13sus4 you can use either the A minor or the E minor pentatonic scale. Over F13sus4 you use the C minor or the G minor pentatonic scale. Enjoy!