“Air” is a free composition written with harmonies based upon fifths rather than traditional harmonies based upon thirds.
Being a fifths-based harmony might be thought of as being essentially the same as a fourths-based harmony (being its inversion) which was the structure used in the Minuet in G, Stretched piece, also described on this blog. But the harmonic approaches in these two pieces is quite different.
In the Minuet piece, the fourths-based harmony was mapped from a thirds-based harmony in a more or less direct translation of the patterns of the one into the other. In other words, primary attributes of the traditional thirds-based harmonic relationship structure were used while the underlying intervals were changed—kind of like taking a photograph then stretching one of the dimensions in Photoshop.
In the case of the fifths-based harmony used in Air, there are two major differences. First, the harmonic progressions in Air were not in any way mapped from traditional progressions. The harmonic choices were made solely on the basis of their colors. Second, the harmonic tones were not limited to a traditional scale as they were in the Minuet—meaning, in the Minuet all the tones were taken from a classical minor scale, while in Air there is no such restriction.
Not being constrained to a traditional scale, many of the arpeggiated harmonies in Air veer off into potentially dissonant note groupings. But, with the dissonances placed in higher octaves the effect is not as harsh as if these tones were found among the lower pitches. This effect can be compared to natural harmonics where the naturally occurring higher harmonics would be quite dissonant if they were in the same octave as the fundamental tone, but as they exist in higher octaves the effect is quite different. Certainly this piece, Air, brings those higher harmonics much closer to the tonic, and relatively louder, than they are within the typical harmonic series; yet the effect, I think, is still quite consonant in feel.