How to Write a Bass Line: Root Notes and What Bass Players Play
String together the notes a bass player plays through a song and you get a line: the bass line. In a band, bass is what ties harmony and rhythm together: it states the foundation of each chord and holds the pulse with the drums. A good bass line often goes unnoticed, but take it away and the bottom falls out of the song.
Someone new to the band picks up the chord chart: C, G, Am, F. The guitarist knows what to do, they'll play the chords. For the bass player the question is different: which notes, in what rhythm, go under those four chords? Most of the answer is already written on the chord chart.
What does a bass player actually do?
Bass has two jobs. The first is harmonic: it tells everyone which chord the song is on, from the bottom up. Even when guitar and keys play the chord, the ear picks up chord changes mostly from the bass. The second is rhythmic: together with the drums, it carries the tempo and feel.
That's why most notes in a bass line come from the chord itself. The ones that get the most weight are the root, the third and the fifth. The steps below start from those three.
What's a root note, and why start each chord on it?
The root is the note the chord is named after. The root of C is C, of G is G, of Am is A. The letter on the chord chart already tells the bass player the first note to play.
Playing the root when the chord changes is the clearest way to tell everyone about the change. So the first rule is: play the root on the first beat of each new chord. For a start, just playing roots in straight eighth notes gives the band a solid floor. Plenty of rock bass lines are exactly that.
If chord symbols are giving you trouble, how to read chords covers the basics.
What do fifths and octaves add?
Roots alone are solid, but they can start to feel flat. The first two notes to add are the fifth and the octave. The nice thing is they always sit in the same place relative to the root.
- Fifth: One string up, two frets along from the root. If you're playing A on the 5th fret of the E string, its fifth is E on the 7th fret of the A string.
- Octave: Two strings up, two frets along. The same note, an octave higher.
A few basic patterns built from these give you different feels:
| Pattern | Over C | Feel |
|---|---|---|
| Root only | C, C, C, C | Simple and driving |
| Root and fifth | C, G, C, G | Gently rocking, balanced |
| Root, fifth, octave, fifth | C, G, C (high), G | More movement |
| Root, third, fifth (arpeggio) | C, E, G, E | Melodic, shows the chord's colour |
How do chord tones make a bass line richer?
Playing the notes of a chord one after another is called an arpeggio. Add the third to the root and fifth, and the bass line turns melodic. But watch one thing: the third is the note that makes a chord major or minor.
The third of C major is E, of C minor is E flat. In Am the third is C, in A major it's C sharp. Miss the "m" on the chart and play the wrong third, and the chord sounds off even when the guitar plays it right. Since the root and fifth are the same in major and minor, sticking to those two on a chord you're unsure of is the safe choice.
Where do passing and approach notes go?
To smooth out the move between two chords, you can use a note a half step below or above the next chord's root. That's called an approach note. For example, going from C to F, play E on the last beat of the bar and step up to F.
Approach notes have two rules:
- Put them on a weak beat. Beat 2 or 4, or between beats. A note outside the chord on a strong beat can sound like a mistake.
- Resolve straight away to a chord tone. An approach note doesn't mean much on its own. It makes sense because of where it's going.
Using them sparingly matters too. A bass line with an approach note at every change starts to sound busy fast.
How does it all come together over four chords?
Back to the C, G, Am, F from the start. Say each chord lasts one bar of four beats. A simple line built from roots, fifths and approach notes could look like this:
| Bar | Chord | Notes | What's happening |
|---|---|---|---|
| 1 | C | C, G, C, F sharp | Root and fifth, approaching G on the last beat |
| 2 | G | G, D, G, G sharp | Root and fifth, approaching A on the last beat |
| 3 | Am | A, E, A, E | Root and fifth, and the last E also sits a half step below F |
| 4 | F | F, C, F, B | Root and fifth, approaching C to loop back |
Play it with just the roots first, then add the fifths, then the approach notes. Listening to how the band sound changes with each layer makes it easier to decide what suits the song.
How do you get started with walking bass?
Walking bass is a line that "walks" in even notes, usually quarter notes. It's all over jazz and blues, mixing chord tones, scale notes and approach notes.
A simple pattern is enough to start: root on beat 1, other chord notes on beats 2 and 3, and on beat 4 a note a half step away from the next chord's root. Try it over a 12-bar blues. The chords don't change too often and the cycle is predictable, which makes it good practice.
What does the bass play on a slash chord like C/E?
Sometimes a chart shows chords with a slash, like "C/E." The chord is on the left of the slash, the bass note on the right. So on C/E the guitar plays a C chord and the bass plays E. E is already the third of C, so the chord stays intact, but the bass takes a different, usually smoother path.
When you see a slash chord, playing just the note on the right for as long as that chord lasts is usually the right move. Whoever wrote the song picked that bass note on purpose.
When should a bass player play less?
Space in a bass line is a choice too. If the rhythm guitar is busy, the keys player is covering bass notes with the left hand, or the vocal is up front, keeping the bass simple makes the song clearer. In rock and pop, not getting in front of the vocal is a good general rule.
The best way to play less but play right is to land with the kick drum. Hitting the root where the kick hits puts a solid floor under the band.
When the band changes a song's key, the bass player's maths starts over. In BandUp's lyrics and chords editor, transposing shifts all the chords and the key together. In Stage Mode, live transpose moves the chords to the target key and the change shows up on every member's screen instantly. So the bass player can read the new roots off the screen instead of working them out on the fly.
How that relationship works is really the answer to what is groove.