How To Arrange A Great Bass Line For Any Chord Progression

by Anthony Gore

 

This article presumes a basic understanding of chords. If you are unfamiliar with the theory behind chords, or you could do with a brush up, take this 5-minute lesson before reading on: http://www.musictheory.net/lessons/html/id40_en.html

 

The simplest way to arrange a bass line under any chord progression is to use the tonic note of each chord as the bass note, as shown in the example below.


Ex. 1: tonic note of each chord used in bass

There’s nothing wrong with this approach, but there are methods we can use to create a variety of other interesting bass lines for this same progression, namely by using inversions and passing notes.

 

Inversions

Instead of using the tonic in the bass, you can use other notes from a chord in the bass i.e. the third, fifth or seventh. Chords with notes other than the tonic in the bass are known as "inversions". An inversion of a chord, while technically still the same chord, has a slightly different character of sound.

Generally inversions are written with the chord name, followed by a forward slash, followed by the note that is in the bass. For example, D minor with a C in the bass would be written Dm7/C.

 

"Smoothness"

Why use inversions? You may prefer the sounded of an inverted chord, which is reason enough, but generally their purpose is to ‘smooth out’ a bass line.

When we refer to a "smooth" bass line, we’re talking about one that is not angular; the movement between one note to the next is not in large leaps, but in smaller steps. Look at the shape of the bass line in Example 1 above, and compare that to bass line in the example below, which has the same chords as example one, but smooths out the line by using inversions of the chords.


Ex. 2: similar to Example 1, but utilises inversions.

Essentially, inverted chords give you extra flexibility when writing a bass line, allowing a variety of chord changes to sound smooth where they may have sounded awkward if you only used the tonic in the bass.

 

Harmonic Stability

On the flip side, good bass lines also make the chord progression sound harmonically stable. This concept is best explained through an example:

Ex. 3: inversions on every chord

You’ll see here that every chord is written in inversion. Even though the bass line is very smooth, the sound is quite unstable. Without using some tonic notes in the bass line, the ear becomes disconnected. This may be a desired effect, but most of the time it will not be appropriate.

Consider that in Example 1, where we have a reasonably unsmooth line, the bass line sounds much more "right" than that of Example 3. This is because the line in Example 1 creates perfectly stable harmony, due to the exclusive use of tonic notes. The point is that while it’s important for a bass line to be smooth, it generally should not be at the expense of harmonic stability.

With harmonic stability in mind, there are three guidelines to consider when using inversions:

  1. They should not be used too generously, or the chord progression will sound unstable.
  2. The position of the inverted chord matters. ‘Strong’ points of the chord progression generally won’t be appropriate for an inverted chord, such as the first and last chord of the progression, and perhaps on the first beat of bars within the progression. Inverted chords suit weaker points much better, e.g. in the middle of the bar and on off-beats. The strong and weak points are different for every progression, so you will have to use your discretion when making such decisions.
  3. One inversion following another sometimes won't sound as good as one inversion between two non-inverted chords.

 

Passing notes

An additional way to make a bass arrangement interesting is to use "passing notes".  These are notes that do not fall on the same beat as the chord, but are there to bridge between two chords.


There are two varieties of passing notes to be mentioned:

  1. Tonal passing notes. These are notes that do not occur in the chord, but do come from the key of the progression. In Example 4, below, the passing note between the Cm chord and the Eb chord, i.e. the D in the bass, is a tonal passing note, as D belongs naturally in the Cm key.
  2. Chromatic passing notes. These are notes that do not belong to the chord, or the key. In Example 4, the E that falls between the Eb chord and the Fm chord would be considered a chromatic passing note, as E is not in the Cm key (hence the natural accidental). Usually chromatic passing notes will be one semitone below the ‘destination’ note, (e.g. the E is one semitone below the destination F in bar 2) as this gives a "leading into" effect.

Ex. 4: a progression with passing notes

Like inversions, passing notes should not fall on strong beats, but should occur only in passing, as the name suggests. They are usually used, again, to smooth out the bass line.

Summary

 

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