Musical Consonance

In the psychology of music, consonance involves the relationships between two notes played simultaneously, which distinguishes it from both harmony (involving relations amongst three or more simultaneous notes) and melody (involving sequences of single notes) (Seashore, 1938/1967).  As a result, the foundation of consonance is the musical interval, the relationship between the frequencies of the two notes.  Western music is based on a relatively small number of intervals, unison (frequency relationship of 1:1), minor second (27:25), major second (9:8), minor third (6:5), major third (5:4), perfect fourth (4:3), tritone (25:18), perfect fifth (3:2), minor sixth (), major sixth (10:3), minor seventh (9:5), major seventh (15:8), and perfect eighth or octave (2:1).

Psychologically speaking, there are two major issues concerning consonance.  The first is the division of a scale into tones according to consonance.  For instance, why does Western music employ scales based on 12 musical intervals?  According to Seashore (1938/1967, p. 128) “on the whole, our present half-tone step is as small a step as the average of an unselected population can hear with reasonable assurance, enjoy, and reproduce in the flow of melody and harmony in actual music.”  This claim is based on the results of studies on musical psychology carried out in Seashore’s laboratory.  The second involves the quality of different consonances: some are more aesthetically pleasing than others.  For instance, the most pleasing are unison and octave consonances, followed by the perfect fifth and the major third; the tritone is the most displeasing (Krumhansl, 1990).  What is the source of how pleasant a consonance is?  Many researchers have followed the proposal of Helmholtz (1863) that the aesthetic value of consonance is directly related to the frequency ratios; some ratios produce larger numbers of beats that provide a roughness to the tone, and this roughness decreases ratings of pleasure.

References

1. Helmholtz, H. v., & Ellis, A. J. (1863/1954). OnThe Sensations Of Tone As A Physiological Basis For The Theory Of Music (2d English ed.). New York,: Dover Publications.
2. Krumhansl, C. L. (1990). Cognitive Foundations Of Musical Pitch. New York: Oxford University Press.
3. Seashore, C. E. (1938/1967). Psychology of Music. New York,: Dover Publications.

(Added November 2010)