Create Your Own Scales Using Tetrachords

As film composers, we’re often called upon to create novel sounds. Genres like sci-fi and fantasy often require unique and unfamiliar music to effectively conjure up alien atmospheres or magical lands. There are a number of ways to achieve these effects—exotic instruments, bizarre synthesized sounds and unusual combinations of effects often work. But sometimes it’s best to conjure the unexpected musically rather than with orchestration or production. Here’s a neat trick to create interesting scales using tetrachords.

A tetrachord is a series of four notes, usually arranged within the space of a fourth (true tetrachords as developed by the ancient Greeks spanned a perfect fourth, but for our purposes augmented or diminished fourths work just as well, if not better). An easy way to think if them is as half of a standard seven-note scale. The pitches C-D-E-F form what’s called a major tetrachord, which also happens to be the bottom half of a C major scale. The pitches G-A-Bb-C form a minor tetrachord—the bottom half of a G minor scale. Put the two together and you get a C Mixolydian scale.

What if you substituted the bottom half of a G Phrygian scale as the top tetrachord: G-Ab-Bb-C. Then you’d end up with a much more unusual scale—a C Mixolydian Flat 6 scale, a mode of the melodic minor scale. You may never have heard of the Mixo Flat 6 scale, but if you’ve ever watched a science fiction movie I guarantee you you’ve heard it:

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Listening to the entire scale, you can really hear how it sounds like two half-scales put together:

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Incidentally, the Mixolydian Flat 6 scale is actually the dominant mode of F melodic minor. Using tetrachords in this way will often yield modes of the melodic or harmonic minor scales, or modal scales with one or two altered notes (after all, there are only so many seven-note scales in an octave). Even so, using tetrachords encourages you to think outside the box, and even if you end up with a pre-existing scale, you may not be familiar with it and wouldn’t have thought to use it otherwise.

Here’s a more bizarre example—a minor scale on the bottom and a octatonic scale on the top (C-D-Eb-F-G#-A-B-C, or a C melodic minor scale with a raised fifth). If you’re looking for a truly odd result, use more unorthodox scales like the octatonic, whole tone or harmonic minor scales for at least one of the tetrachords. And remember that your scale can include thirds as well as seconds:

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(To take this example further, you could add an F# or G in the middle of the scale to make an 8-note scale. It’s outside of the realm of true tetrachords, but we’re just using the technique to achieve a particular effect anyway and don’t need to worry too much about rules.)

As you can hear, this approach can take you to places you may not have otherwise gone. Experiment with it and see what you come up with. Choosing more unusual tetrachords will obviously yield more exotic results. Be aware of using two or more half steps in a row in your scale. It’s perfectly OK to do so, and the results will definitely sound unconventional, but they will also feel less natural since there are no standard Western scales or modes with two or more sequential half steps. Once you have a scale you like, you can work out the accompanying chords by playing the root, third and fifth of each note of the scale, making sure to only use notes diatonic to the scale. Use your new scale to create melodies and whisk your audience into strange and unfamiliar worlds.

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