Symmetric Scales (feat. Debussy and Messiaen)

Next to the more common diatonic scales there exists a type of scales that is known as symmetric scales or modes of limited transposition.

In many cases both terms mean the same thing but focus on different properties of these scales.

Such a scale is being constructed by dividing the octave into groups of repeating intervallic patterns.

For instance dividing an octave into 6 whole tone steps such as C, D, E, F#, G#, A#, C would be considered as symmertric scale.

Contrary to diatonic scales that introduce new pitch material with every transposition to any of the 12 possible keys, when you transpose symmetric scales to the 12 different keys you will find that you might end up with exactly the same pitch material in some cases.

For instance with our scale from above we could only start it either on C or on C#. Any other transposition would result in either of the two pitch materials again. They are "modes of limited transposition".

The two most well known of such scales are the whole tone scale from above and the octatonic or diminished scale that is constructed out of the repeating patterns of whole-half or half-whole.

So much for the dry theory on this. For composers/arrangers these scales can open up an interesting palette of harmonic colours. Their property of being symmetric removes their tonal gravity as they have several notes that seem to function as a root note. For instance the whole tone scale outlines an augmented triad and the chords of C+, E+ or G+ contain exactly the same notes therefore remaining very ambiguous.

The same happens with the diminished scale which outlines several interchangeable diminished triads.

This lack of tonal gravity can be used to great effect.

Let's have a look at a great example by Claude Debussy, called "Voiles" which means veil.

https://www.youtube.com/watch?v=FVV0jkZC4jI 

Debussy uses the whole tone scale here and the effect of these veils floating in the wind feels very striking with this scale. However, you might also note that the harmonic feeling remains rather static. Other than with diatonic scales where the chords that you can derive from that scale are capable of creating different degrees of tension and release, with symmetrical scales, all chords that you can derive from them seem to be rather similar.

In a piece like the one above, which is supposed to be static and "float" in the tonal space, this property is very desirable. However in a piece that you want to propel forward harmonically this can become the weakness of these scales.

In many cases it works best to use these scales on a per bar or a per section basis. However, it is also possible to source entire pieces out of these scales if you use their presence a bit more liberal and more as a central but not an exclusive property.

In my piece Diamond Heist, the diminished scale plays a very central role throughout the entire piece:

https://www.youtube.com/watch?v=OMtofzhBmmo 

One composer who dedicated a lot of his work to these scales was Oliver Messiaen. He compiled a list of all possible such scales and came up with seven possibilities within the range of our tempered tuning system:

There are more scales than those that you could consider to be symmetric but they are all truncations of one of these seven scales. For instance the scale of 1-3 or 3-1 (meaning semitone-minor thid or vice versa) which is very popular in action scoring is a trucation of the third mode.

In general one can say that these scales, particularly the first three, are quite commonly used in scoring. There exist even some cliché uses, like the whole tone scale is often used for dizzyness or "drug experiences". Also, the "beaming" sound effect in Star Trek is a whole tone scale cluster.

Even more cliché are diminished harp glissandi that introduce a dream sequence or in general diminished scale runs that have a quality of fantasy to them. But also rather agressive and chaotic action sequences often rely on the diminished scale.

It is definitely well worth exploring these scales and developing a feeling for how they sound and what kind of emotional response they create in order to use them as part of one's own musical vocabulary.

For practice purposes, it might even be advisable to try to come up with a small piece in each scale to explore the musical possibilities they provide.