Project 13 is about dressing up the tonic/dominant relationship, which I will look at closer here. There is a special, almost gravitational affinity between two tones pitched perfect fifth apart. Many theorists use the physical nature of the overtone series to explain the gravitative inclination between a tone and its perfect fifth, pointing out the fifth as the first and the strongest overtone after the octave transposition of the fundamental. In other words, as Sorce (1995: 135) explains:
“When a body is set into vibration, it is not only fundamental (initial pitch) that sounds, but also an infinite number of additional pitches, known as overtones or partials… The first overtone to be set into motion is the octave; the second is the 5th, or dominant.”
Not only is the relationship between a tone and its 5th a natural law in the overtone series, but as he continues, it’s “a unifying factor in the establishment of the tonic-dominant relationship”. (Sorce, 1995: 136) Thus, the interval of perfect 5th underscores the most essential harmonic relationship of the tonal music – the tonic/dominant relationship, but it is also important for the tuning systems and the concept of the circle of 5ths, which groups and outlines the tonalities of the diatonic scales in a specified order. But back to the tonic/dominant relationship, it should be mentioned that within a certain key, there can be moments when other degrees receive the role of the tonic – a musical procedure called tonicization. It is the secondary dominant, with its perfect fifth relationship to the temporary tonic, that produces the suggestion of a new key centre. In modern music, where the chords can be built by stacking perfect 5ths – called quintal chords, as the project 13 brief also pointed out, a strong fifth can create the illusion of the tonic/dominant relationship even if it has nothing to do with the actual key.
Whether describing a genuine tonic/dominant relationship, a case of tonicization with a secondary dominant, or an illusion of the tonic/dominant connection, the role of the perfect 5th is so tied to this harmonic progression, as Sorce (1995: 136) describes, “so unifying, in fact, that it is difficult, if not impossible, to destroy this [tonic/dominant] relationship with any pitches that may be superimposed.” In this way, the project 13 with the aim to dress up the tonic/dominant harmony, proves that any notes placed in-between can hardly distract when a strong dominant chord is followed by the expected tonic resolution. Take a look at the short examples I composed for Project 13. You can also take a look at the cadenzas I listened to in my listening log here.
Sorce, R. (1995) Music Theory for the Music Professional. US: Ardsley House Publishers Inc.