How to Write a Bass Line

The bass has two jobs at once. It tells the ear which chord is sounding, because the lowest note decides how you hear everything else. And it's part of the rhythm, almost as much as the drums. A good bass line does both at the same time. We'll start from the simplest possible line and build it up step by step, over the Am, F, C, G loop you know by now.

The note that decides the chord

Before writing a line, try this experiment. Keep the three notes A3, C4 and E4 on the piano, an A minor chord, and change only the note played underneath.

With A underneath, you hear an A minor chord, nice and stable. With F, the same chord becomes an F major chord with a major seventh added, Fmaj7, softer and dreamier. With C, it sounds less settled, like an inverted chord. The three upper notes didn't move: only the bass changed what you hear. That's why a bass that plays any old note from the scale can undo chords that were well written in the first place.

The root, then the octave and the fifth

The simplest line plays the root of each chord, the note that gives the chord its name, once per bar. It's always right, and you hear it in a lot of tracks, often as held notes under pads. It has just one flaw: it hardly moves.

The first way to bring it to life is to add the octave, the same note twelve semitones higher. The bass jumps from A2 to A3 and back. Since it's the same note, the harmony doesn't change, but the movement creates a bounce. The second way is to add the fifth, the note seven semitones above the root, which is also part of the chord. That's E for Am, C for F, G for C and D for G. Listen to the bass on its own, with these three notes.

You heard it: the line moves a lot more, and yet it never clashes with the chords, since it only plays notes that belong to them. You can also put the fifth below the root, which gives a very steady motion, like a pendulum. Root, octave and fifth form the skeleton of a large share of bass lines, in almost every genre.

Passing tones to connect the chords

Like a melody, the bass can borrow passing tones to get from one chord to the next. Between A and F, it can go down through G; between C and G, through B and A. Placed at the end of the bar, right before the change, these notes make it sound as if the bass is walking toward the next chord.

There's a spicier version: the chromatic approach note, which arrives on the next root from the semitone just below or just above. For example, a G♯ right before the A that starts the loop again. This note is outside the scale, but it's so short and resolves so quickly that the ear hears it as momentum rather than a mistake. Use it sparingly, on an eighth note or a sixteenth note.

Listen especially to the ends of the bars: each time, the bass announces the chord that's coming. A bass like this is said to “walk,” an idea that comes from jazz and that you find, in more discreet forms, in funk, house and R&B.

Syncopation and anticipation

So far, the bass hits mostly on the beats. Now shift some notes onto the offbeats, or hold a note over a strong beat: you get a syncopated bass, which instantly adds groove. You discovered syncopation in the part on rhythm; applied to the bass, it often makes the difference between a stiff loop and a loop that dances.

One special case deserves its own name: anticipation. The bass plays the root of the next chord a little before the change, an eighth note or a sixteenth note before the bar line, and holds it over. So the chord arrives from below first. This small shift, typical of a lot of Latin music and also common in pop and house, gives a feeling of forward momentum.

Look at the grid: few notes start right on a beat, and the F2 starts before the bar line. For the anticipation to work, the anticipated note has to be held over the change or followed by a silence. If you play it again on the first beat, the effect mostly disappears. The last A2, for its part, announces the loop coming back to Am; since the loop plays it again on the first beat, it isn't a true anticipation.

Bass and kick: line up or stay out of the way

The bass shares the low register with the kick. The two often occupy the same frequencies, and their rhythmic relationship matters enormously. There are two main strategies, and many tracks combine both.

The first is to line the bass up with the kick: every time the kick hits, the bass plays too. The impact is massive, and that's often the case in trap, where the 808 largely follows the kick's rhythm. The second is to have the bass play between the kicks. In house and techno, a bass on the offbeats, between two kicks of the four-on-the-floor, is a classic: the kick takes the beats, the bass takes the gaps, and each one keeps its place.

Listen to how the two lock together: the kick and the bass never step on each other. When you line them up instead, check that they aren't fighting over the same frequencies; the next lesson will show you how to tune the kick to the 808. Many producers also add compression triggered by the kick, called sidechain, which ducks the bass for a brief moment on every hit. It's a mixing tool, but it carries this same idea of sharing the space.

In the next lesson, we stay in the low end with a rather special kind of bass, the 808, which raises its own tuning questions.