Altered chord


Audio: altered chord (0:04)

Altered chord
Figure: altered chord

altered chord plays an altered chord on cornets and trombones. The altered chord figure shows the score.

An altered chord is a chromatic chord containing one or more notes that are not part of the prevailing key.

At home, I have a book, published in 1960, called 500 Advanced Chord Shapes for the Guitar. Whilst writing the guide I opened it at random and chose the most complex chord on the page. It was labelled Eb13(b9+11). I quietly closed the book and briefly pondered why it was 50 years since I last read it.

Writing an altered chord is simple: any note in any chord can be altered. Notating it, though, is not for the faint-hearted.

To write a 13(b9+11) chord, construct the unaltered chord first, then alter the notes. A thirteenth chord labelled 13 is built from a dominant seventh chord and contains an interval of a thirteenth, an octave plus a sixth. The chord is altered by flattening the ninth, b9, and augmenting the eleventh, +11. The result is a seven note chord containing two chromatic notes (three if you count the minor seventh above the root).

And what a wonderful chord it is too. Unfortunately, it is unplayable on a guitar. A guitar has 6 strings, the chord has 7 notes. Something has to give. That something is the root note. It is omitted because the rest of the notes are said to imply the existence of a silent root.

Wish someone had told me this all those years ago.

Every altered chord must contain at least one accidental. The presence of an accidental is a good sign that a chord is an altered chord. It is not, however, foolproof. Some chords with accidentals are diatonic chords. For example, the chord Bm7b5 looks like an altered chord. It contains the notes, BDFA. These notes are part of the key of C major. Bm7b5 is diatonic in the key of C major and is numbered vii7b5.

What is interesting from the perspective of a jazz writer is when and why an altered chord is used. One obvious reason is to add variety to a piece of music, an altered chord provides a fresh sound. Another reason is to harmonise a given melody. Another is that it can be constructed from a scale other than the usual major or minor scale. A less obvious reason, used in altered chord, is that it is constructed from two or more simultaneous and different keys and voiced using the technique of upper structure voicing.

Upper structure is a method for voicing a jazz chord. The technique can be applied to a seventh chord, an extended chord or an altered chord. The lower structure contains the lowest pitches and is voiced in the bass staff. It contains the two guide notes in a seventh chord, the third and the seventh above the root. The upper structure, the highest pitches in the treble staff, contain the rest of the notes. Typically, these form a major or a minor triad although it can also be some other type of chord.

A complete C7b9 chord, for example, contains the notes, CEGBbDb. It would be voiced EBb in the lower structure, the guide notes forming a tritone, and representing an incomplete seventh chord. The remainder of the notes, CGDb, are voiced in the upper structure. They form a chordioid, a lovely but little used term for a nontertian chord. This voicing has an ambiguous tonality. Alternatively, the upper structure notes can be respelled to form the enharmonic chord, CEbG, a C minor triad. The lower structure is then deemed to be in the key of C major, and the upper structure is in the key of C minor.

A chord in upper structure voicing can be incomplete. The fifth is often omitted in a seventh chord and its extensions, the root can be omitted in a big chord, and any note can be doubled. An incomplete C7b9 chord, for example, could consist of the four notes EGBbDb, without the root. The tritone, EBb, can be voiced in the lower structure, and an incomplete E minor seventh chord, EGDb, constructed in the upper structure by doubling the note, E. This C7b9 chord voicing straddles the keys of C major and E minor.

altered chord combines the idea of multiple tonalities with the technique of upper structure voicing to create a C13(b9+11) chord. The complete chord contains the seven notes C E G Bb Db F# A. Four of these notes, CEGBb, form a C7 chord and are played by the cornets. The remaining three notes DbF#A are rearranged to form the enharmonic chord, F#AC#, an F# minor triad. Note E is doubled to extend F#m to F#m7 and the chord is played by the trombones. The final chord combines the C7 chord and the F#m7 chord together in an incomplete C13(b9+11) chord in which the root, C, and the fifth, G, are omitted. Two guide notes in the C7 chord, the tritone, EBb, are voiced in the lower structure, the remaining notes are voiced in the upper structure, ADbF#, to form an enharmonic F#m triad. This voicing straddles the keys of C major and F#minor.

Thinking of a chord as an entity with multiple tonalities is a very productive way to write jazz harmony. It can also be used to write chromatic harmony because it is the basis of polytonality.