Aversion to Clashing Harmonies is Due to Mathematical Relationships of Overtones

November 13, 2012

Biology

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Image courtesy of flattop341/Flickr

There are many people who dislike clashing dissonances of some modernist composers. It’s been long thought that dissonant musical chords contain acoustic frequencies that interfere with another, disturbing people. Now, a new study indicates that humans prefer consonant chords because of the mathematical relationship between the many different frequencies that make up the sounds.

The scientists published their findings in the journal Proceedings of the National Academy of Sciences. Marion Cousineau, a cognitive neuroscientist at the University of Montreal in Quebec, and her colleagues evaluated the preference of consonance over dissonance by comparing the responses of a control group of people with normal hearing to those of people with amusia, which is an inability to distinguish between different musical tones.

Consonant chords are made up of notes that seem harmonized whereas dissonant chords are combinations that sound jarring. The reason why people like one over the other has perplexed musicians and cognitive scientists.

It’s been suggested that there is an innate human preference for consonance over dissonance, leading some to believe that dissonant music is unnatural and sounds bad. Others, like composer Arnold Schoenberg, have argued that dissonance is merely a matter of convention, and it’s possible to like these sounds.

It has also been thought that there was some kind of physiological reason why some dissonant sounds are jarring. Two tones close in frequency will produce a beating, made from when a single tone is rising and falling in loudness. If the difference in frequency is within a certain range, rapid beats create a rattling sound that’s called roughness. An aversion to roughness seems consistent with the dislike of intervals like minor seconds.

Amusic subjects in this study showed no distinction between any of the intervals; whereas normal-hearing people thought that small intervals and large but sub-octave intervals and major sevenths were very unpleasant.

The researchers also tested how the groups felt about beating. They discovered that amusics could hear and disliked it as much as the control group. So apparently something else was causing the latter dislike in the dissonant intervals.

These preferences seem to come from the harmonicity of consonant intervals. Notes can contain overtones, frequencies that are whole-number multiples of the basic frequency in the note. For consonant intervals, the overtones of two notes coincide as whole-number multiples, whereas for dissonant intervals, this isn’t the case. The dissonant intervals are more like irregular overtones, and don’t sound harmonic.

The control group preferred intervals with regular harmonic relationships over artificial consonant ones, in which overtones were shifted into the inharmonic range. The amusics registered no difference between the two cases, which implies that they are insensitive to harmonicity.

[via Nature]

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