In a recent article in PLoS ONE, Kamraan Gill and Dale Purves examined the issue of why only a few of the enormous number of possible tone combinations are employed to create music.
They began their article with a brief description of the musical scales that have been widely employed in world music, noting that the same five-note and seven-note collections that are used in major and minor pentatonic and heptatonic scales of Western music are also prevalent in traditional Indian, Chinese and Arabicin music. This lead to the question of why only a few scales have been so strongly favored (i.e., since there are billions of possible ways to divide octaves into five to seven tonal intervals, is their a reason why a particular set of these has become so well established?).
Gill and Purves investigated the idea that the scales that have been preferred in music worldwide share an overall similarity to the spectral characteristics of a harmonic series. To do this, they quantitatively compared the harmonic structure defining each interval in a possible scale to a harmonic series. With this in hand, they could then ascertain whether the scales with the highest degree of similarity to a harmonic series are in fact the scales commonly used to make music.
Of course this approach meant that they had to evaluate all "possible scales", a huge task. They did not do this, but selected a subset of scales by restricting the potential scale tones to 60 (leaving 455,126 pentatonic scales, 45,057,474 heptatonic scales and 279,871,768,995 dodecatonic scales).
The results were expressed in terms of the highest mean percentage similarity to a harmonic series. The most similar scale to a harmonic series was the minor pentatonic scale. The second most similar was the Ritusen scale and the third and fourth most similar, the ascending forms of two ragas (Candrika todi and Asa-gaudi) used in classical Indian music. Interestingly, the chromatic scale did not appear that similar to a harmonic series when compared to 10 million other possible 12-note scales. They summarize the results by stating that musical scale preferences are predicted by the overall similarity of their component intervals to a harmonic series (here "musical scale preference" is being used as a short-hand denoting the popular scales that exist in world music).
In the discussion, Gill and Purves considered the basis for why the component intervals of existant musical scales are similar to a harmonic series. They proposed that the use of such scales derives from a preference for tone combinations that reflect the spectral characteristics of conspecific vocalizations.
What do you think?
Gill, K. & Purves, D. (2009) A Biological Rationale for Musical Scales. PLoS ONE 4(12): e8144. doi:10.1371/journal.pone.0008144