Pentatonic scale / Whole-tone scale / Octatonic Scale
The octatonic (eight-note) scale is a series of alternating semitones and tones. Many twentieth-century composers (including Debussy, Stravinsky and Bartok) have written melodies based on it.
Composers from in the nineteenth century also used the octatonic scale, particularly Russians like Rimsky-Korsakov, and the resulting harmony is very interesting and exotic sounding.
On this page, we are going to look first at the scale itself and how it might be used melodically and then explore the harmony in the bit more detail.
This is an octatonic scale starting on D# (there are only three unique octatonic scales possible before you start repeating the same scales starting on different notes). In this example I have divided it into two four-note segments (or tetrachords). You might notice that W and X individually are simply the first four notes of the minor scale – it is the combination of these two tetrachords a semitone apart that creates the distinctive octatonic sound.
In this simple duet for two violins, Bartok really takes advantage of the unfamiliar juxtaposition of two segments from the minor scale. The upper violin plays a melody based on the X tetrachord and the lower one uses the Y tetrachord.
Bartok, Song of the Harvest
Later on in the same piece, he uses a different octatonic scale starting on G#, but this he uses strict imitation, imitating at the interval of a tritone to keep within the octatonic scale. Notice how Bartok is not really worrying too much about the harmony, concentrating more on line. He lets the imitation take care of the melodic details and the relationship between the two tetrachords take care of the overall harmonic effect.
Another way of showing the octatonic scale is as two diminished seventh chords a semitone apart (C and C# in the example):
We saw with octatonic melody that it creates something familiar (segments of the minor scale) and something unfamiliar (the way they are combined) and it is the same with octatonic harmony.
It is possible to get lots of familiar chords by building them on the four notes of the LOWER diminished seventh (in this case C). You can see that a major, minor and dominant seventh chord can all be constructed from the notes of the scale by starting on the roots C, Eb, F# and A.
HOWEVER, the unfamiliar bit is that it is impossible to get chords a fifth apart (as in the traditional I, IV and V). All the chords in this sequence are either a minor third apart (e.g C and Eb) or a tritone (e.g. C and F#).
In this extract from Rimsky-Korsakov’s Sadko various chords based on C and F# (a tritone apart) are alternated to create a scene by an enchanted lake. The music is based entirely on the octatonic scale above.
In Debussy’s Nuages, we can see octatonic harmony and melody in action.
In Stravinsky’s Scherzo Fantastique, we can see examples of octatonic scales being used in a fairly flexible way. The dominant seventh chords of E, C#, Bb and G are taken from the same octatonic scale and are a third apart, all four roots making up a diminished seventh as explained above. All this occurs over a B pedal in this example.