A great way to expand the sound of your playing and song writing is to compose your bass lines in a linear way, ascending or descending. Often the bass playing of a song may revolve around moving with the root notes of the chords of a progression. In simple terms if a progressions was G - em - C - D, then the bass would play the notes (or patterns constructed around the root notes consisting of...) G - E - C - D.
A different approach involves selectively using individual notes from chords to create a more linear bassline. It's a great style that has been used in scores of hit songs for decades, and of course goes back to jazz and classical styles. In the example above you could try the bass line G - B - C - D, only playing root notes.
The example shown below is in the key of d minor and uses a descending bass line behind the d minor chord. The traditional score is quite simple, as is the guitar tab. It's not very rhythmic as the example is composed for one instrument only. You can see quite clearly a descending bassline behind a d minor chord. If you have more than one instrument you can get a bit more dynamic with the actual playing of the song with one person playing the chords and the other playing the bass line.
If you want to try the bassline against a chord progression try the chords d min, C Maj, B Flat, F Maj. You can vary your style during your song. Perhaps play solid root note bass during verses and switch to a moving pattern like the example during choruses. Have fun and experiment!
One last point for guitarists- if you're working at playing this line solo you may need to let the bottom e string ring open to create the chord you need. This will actually be a Dsus2/Bb and in context creates a great airy/atmospheric sound. Use your pinky finger to play the C note in bar 1.
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