Tuning, Tonality, and Twenty-Two-Tone Temperament Paul Erlich (
[email protected]) (originally published in Xenharmonikôn 17, Spring 1998; revised 4/2/02) Introduction Western modal and tonal music generally conforms to what is known as the 5-limit; this is often explained (e. g., by Hindemith) by stating that the entire tuning system is an expression of integer frequency ratios using prime factors no higher than 5. A more correct description is that all 5-limit intervals, or ratios involving numbers no higher than 5, aside from factors of 2 arising from inversion and extension, are treated as consonances in this music, and thus need to be tuned with some degree of accuracy. The diatonic scale of seven notes per octave has been in use since ancient Greek times, when harmonic simultaneities (other than unisons and octaves) were not used and the only important property of the scale was its melodic structure. As melodic considerations continued to play a dominant role in Western musical history, scales other than the diatonic had very limited application, and harmonic usage was intimately entangled with diatonic scale structure. It is fortuitous that the diatonic scale allowed for many harmonies that displayed the psychoacoustic phenomenon of consonance, defined by small- integer frequency ratios, as well as many that did not. Medieval music conformed to the 3-limit, the only recognized consonances being the octave (2:1) and the perfect fifth (3:2) (plus, of course, their octave inversions and extensions, obtained by dividing or multiplying the ratios by powers of 2; this “octave equivalence” will be implicit from here on.1) The diatonic scales were therefore tuned as a chain of consecutive 3:2s (Pythagorean tuning).