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Diatonic 7th Variations


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By Ross Krutsinger


Last time in “Using Triad Inversions,” we looked at using different triad inversions to modify, or spice-up, a triad-based bass line.  After mastering the various triad inversions, we are now ready to look at using diatonic 7ths to further modify a bass line.  As before, we will use a bass line similar to the one in Bob Marley’s Keep On Movin’ as our starting place (see example 2)  Thinking in terms of triads, this bass line follows the I-ii chord progression, or, in the key of A, Amaj-Bm.  When considering the 7th chords, these  become Amaj7 and Bm7, respectively.  

In addition to the root position, there are 3 inversions of a 7th chord (see example 1.)  Each inversion of a 7th chord has a different sound, partly determined by the order of the notes from low to high, and partly due to the intervals between the notes.  The root position voicing has the root of the chord as the lowest note, while the first inversion places the root as the highest note.  The second inversion places the root just above the lowest note, and the third inversion places the root just below the highest note.  By looking at the intervals in each inversion of Amaj7 and Bm7, we see that the root position voicing is a series of thirds, where as the 1st, 2nd, and 3rd inversions have two third intervals, and one second interval.  (Many other types of 7th chords exist, but for now we will concentrate only on the major and minor 7 inversions.) 

Example 3 shows the modified bass line that I created last time using triad inversions.  We see that the notes from the original line are the same, but are sometimes displaced up or down an octave.  Using the triad inversions from before gives us a starting place for further modifications.  Since the original bass line does not use the 7th of each chord voicing, we will be creating a line that could sound very different from the original line.  We can still maintain a feel similar to the original bass line, but modifying the line using 7ths involves adding notes or changing notes from the original line.  

Example 4 shows one possible line that could be played when using the various inversions of Amaj7 and Bm7.  This line is much different than our starting point bass line, but maintains the original melodic content.  Notice that the 7th is often used as a passing note and that each 2-beat phrase just adds to the notes from the original bass line.  This line is busier than the original bass line, but it shows one possible way to incorporate diatonic 7ths and their inversions.  This technique is useful in all types of musical situations and becoming familiar with the various inversions of 7th chords and how to apply them gives bassists another tool for creating great bass lines. 


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