Structurally, Fratres consists of a set of nine chord sequences, separated by a recurring percussion motif (the so-called “refuge”). The chord sequences themselves follow a pattern, and while the progressing chords explore a rich harmonic space, they have been generated by means of a simple formula. Fratres is driven by three main voices. The low and high voice are each restricted to playing notes from the D harmonic minor scale (D, E, F, G, A, Bb, C#); the middle voice is restricted to the notes of the A minor triad (A, C, E). The entire piece is accompanied by drones in A and E, which are primarily heard in the refuge between each sequence.The chords are created by the movement of the three voices: the low voice starts at C#; the high voice starts at E. Both the low and high voices are moved up or down the D harmonic minor scale at the same time, with the direction of the movement depending on the position within the sequence. The middle voice starts at A and plays a different pattern (A, E, E, C, C, C, C, A, A, E, E, C, C, A). The generated chords create harmonic ambiguity, since both C# and C are present, yielding an A major or A minor feel.