It is important to understand that when we are creating harmony with our chord progressions we are also creating melody. With any chord progression, there will be a bass line, which is a melody. And often, if we want our song or harmony to stand out, embellishing this bass line can help, and this is what we are calling a “strong bass line”.
A bass line can follow the scale of the key that we are in, or it can behave chromatically, adding complexity to our song’s harmony. In the “Strong Bass Line” video, the first example David gives us is of a bass line that is simply a descending C major scale. So, beginning on C, we simply go backwards in the key of C Major – C -> B -> A -> G -> F -> E -> D and then back to C. This is simple to do, but makes our bass line much more interesting than say, just playing one or two bass notes during the chord progression. If we want to get outside of the key a little bit, we can use the chromatic scale. In the next example David gives us, we are still in the key of C, but we add some new chords to the chord progression in inversion, to give us a nice chromatic bass line.
The first 5 chords of this example are: I C, V G, v g, IV F, and iv f. Inversion is just a fancy way of saying that the bass note is not the root note, but a different note in the chord. So, the C is in root position, but G, Gm, F, and Fm, are all in inversion (the 3rd of each chord being the bass note). If we didn’t put these chords in inversion we wouldn’t be able to get such a smooth chromatic bass line. A bass line of C – G – G – F – F might sound too static, while the chromatic bass line C – B – Bb – A – Ab can make the line interesting.
Often there is not anything wrong with the chord progression we have: we might just be voicing it in a generic or uninteresting way. If we can voice our chords in a way that makes the constituent lines of the harmony compliment the dominant melody/melodies, we can help make a good song a great song.