The opening track of Black Sabbath’s self-titled 1970 album launches off with a jarring tritone, a reverberating note that, when combined with a young Ozzy Osbourne‘s atonal vocals, helped to spark a new direction in rock music.
The unease of Sabbath’s song is rooted, at least in part, in the band’s abuse of dissonance–relying on chords that just don’t “feel” right. But what makes these dissonant sounds so uncomfortable for so many people? New research discussed by Nature argues that people’s general preference for consonant chords over dissonant ones “stem from the so-called harmonicity of consonant intervals.”
Notes contain many overtones — frequencies that are whole-number multiples of the basic frequency in the note. For consonant intervals the overtones of the two notes tend to coincide as whole-number multiples, whereas for dissonant intervals this is no longer the case: they look more like the irregular overtones for sounds that are ‘inharmonic’, such as metal being struck
The aversion to the dissonant notes is not so much to do with the notes themselves, but with the jarring clash of their overtones. To bolster their case, the researchers tested different combinations of notes on people with regular hearing, and with people who were “amusic”—those who can’t tell the difference between two different notes. They found that only the people with regular hearing were bothered by the dissonant overtones. This was not the case for other proposed theories as to why people tend to not like dissonance in their music, such as the reverberations known as “beating” that crop up when two notes that are nearly the same (but not quite) are played together.
The study does not mean, though, that those who love heavy metal or other genres that tend to use (or abuse) dissonance are any less capable of recognizing the clashing chords. Rather, the interchange of dissonant and consonant notes is a powerful method of building and releasing tension in a score, of setting a mood of unease or discontent.
“Rock bands,” says Diana Deutsch to Nature, ”often deliberately introduce roughness and dissonance into their sounds, much to the delight of their audiences,” such as the fans of bands like Sonic Youth, Nine Inch Nails or Tool.
Heavy metal’s propensity for dissonance doesn’t end with the simple tritone, as the flattened supertonic or second is also used extensively to evoke a sense of doom and omen. The flattened second rarely occurs in popular Western music, but is quite common to other musical styles like the Spanish Flamenco, Indian and Eastern European Jewish. Led Zeppelin were masters of contrasting tension and release and would often use these exotic modes to add interest to their compositions. The Led Zeppelin sound was quite influential to heavy metal and the tension created by the flattened second is now a commonplace heavy metal and death metal technique.
Rather than metal listeners being necessarily amusic, it seems instead that they may revel in the unease of dissonance.
Heavy Metal bands use the doom and tension evoked by dissonance to connect with an audience which feels that not all is good in the world and seem alienated by utopian views of modern society.