The science behind why Black Sabbath and Ozzy Osbourne's music sounded ‘satanic'

National Geographic

15 hours ago

Black Sabbath performs during their Heaven and Hell tour in 1980. The band helped revive the long-feared 'Devil's interval'—a dissonant sound once shunned by medieval choirs—as the backbone of heavy metal. PhotographThe idea that two simple notes—not a song, just tones—could be 'banned' may seem ludicrous. But that's the legend behind the crushing opening riff of Black Sabbath's 1970 debut. With just three ominous notes, guitarist Tony Iommi, alongside the anguished vocals of the late Ozzy Osbourne, unleashed a sound so unsettling it was said to have been forbidden for centuries.'Those notes were banned many years ago,' Iommi told the BBC in 2014. 'It's supposed to have been a satanic thing.'
While rock legend has never been the most reliable (see: Ozzy and the bat), this one does have a whisper of truth. Black Sabbath recruited what music theorists refer to as the 'tritone,' —a dissonant interval once avoided by medieval choirs and now known in music lore as the 'devil's interval.' Also referred to as the augmented fourth, diminished fifth, or sharp eleven, the tritone spans three whole tones on a scale, creating a clashing, unstable sound that has long made listeners squirm. But what is it about this ancient musical interval that has unnerved audiences for centuries—and why does it still strike such a primal chord? A history of the 'clang'
Despite its sinister nickname, the tritone was never officially banned in the Middle Ages, though it may as well have been. In the stew of compositional standards of the time, this dissonant tonal interval was merely an unpalatable ingredient, but served in a supremely important dish.
'In medieval and Renaissance music theory, which was often characterised by mathematical and philosophical principles of harmony, the tritone did not fit well into the system of 'perfect' intervals due to its complex frequency ratios,' says Christoph Reuter, professor of systematic musicology at the University of Vienna. Guido d'Arezzo, an 11th-century Benedictine monk and music theorist, developed the hexachord system to help singers navigate early notation and to avoid the dissonant tritone. Photograph by VTR, Alamy Stock Photo Named for medieval theorist Guido d'Arezzo, the Guidonian Hand was a mnemonic device for teaching musical intervals. This version appears in Scienta Artis Musicae, a 1274 treatise by Helia Solomon. Photograph by Giancarlo Costa, Bridgeman Images
One reason for this concerns the relationship between 'scales' and 'modes', the latter of which gives music much of its character. Major scales such as C, for instance, begin on their namesake note. But play the same scale from a different starting point, and it suddenly takes on a very different, but still musical, flavour. These flavors are called modes. Begin a C Major scale on a D, for instance, and you're using the jazzy-sounding 'Dorian' mode. Start it a note up, on an E, and you're in the exotic ambience of the 'Phrygian' mode. The Aeolian mode, starting on A, creates a somber, minor key atmosphere. But one mode stood out for all the wrong reasons.
Things got thorny with the Locrian mode. Built on the seventh note of a major scale—in this case, starting on B in a C major scale—it places unusual emphasis on the interval between B and F. The result is a scale that feels unstable, unresolved, and, to many ears, vaguely threatening.
This was more than a matter of taste. In the Middle Ages, modes were the backbone of choral compositions, used to pitch a choir in harmony. As Reuter explains, not only did the tritone contravene the ideal of musical beauty, but it was also hard. 'It was simply difficult to sing purely—especially in a cappella choral works, which were widely used in the church.' Limited Time: Bonus Issue Offer Subscribe now and gift up to 4 bonus issues—starting at $34/year.
(The hellish history of the devil.)
That difficulty likely gave rise to one of music theory's most ominous warnings: mi contra fa diabolus est in musica, or 'mi against fa is the devil in music.' Referring to the Medieval system of music developed by Guido of Arezzo in the 11th century, 'mi against fa' refers to the dissonance between two tritone notes in overlapping compositions, with the 'devil' likely referencing its tendency to cause mistakes or generally meddle with choral delicacy.
At a time when music was meant to reflect divine order, such instability struck a deeply discordant note.
But uncomfortable tonal combinations weren't isolated to Western music. Many cultural styles—from the Middle East to Japan—had their own 'forbidden' tonal conventions, and different reasons for shunning them.
Similarly to Western modes, certain Indian ragas omit certain combinations of
notes—the varjya svaras—in their compositions, as certain notes are prone to unbalancing this intensely mood-driven music.
Traditional Japanese music, such as gagaku, is often played in formal settings, employing tonal combinations that were sympathetic to the conventions of ma (negative space) and wa (unity), thereby avoiding discordant tones.
By contrast, the Arabian maqam system embraces tonal combinations that Western ears might label dissonant. Its use of microtones and quarter-steps creates melodic tension and release through an entirely different framework of rules.
So is the discomfort we feel from dissonance—like the tritone—truly universal? Maybe not. A 2016 study found that members of the Tsimane', an Indigenous community in Bolivia with limited exposure to Western culture, didn't find dissonant chords any less pleasant to listen to than their more pleasing counterparts. Isabella Czedik-Eysenberg of the University of Vienna believes this shows that 'while dissonant intervals such as the tritone have distinct psychoacoustic properties, the emotional and symbolic meanings attached to those–such as being associated with 'evil'–are likely culturally learned.' This 1970 publicity photo shows Black Sabbath early in their career, shortly before their sound helped shape the heavy metal genre. Photograph by MichaelBlack Sabbath's self-titled debut album, released in 1970, opens with the ominous tritone riff that helped define heavy metal's dark, dissonant sound. Photograph by MichaelWhy does the tritone sound so unsettling? One reason is auditory roughness—the jagged, irregular quality of a sound that our brains often associate with danger, says Czedik-Eysenberg 'Roughness is a particularly interesting audio quality—research indicates it can play a role in communicating danger [and is] a key feature in biologically salient alarm signals, such as human screams,' she notes. 'But auditory roughness also plays a very important part in the perception of extreme vocal techniques used in metal genres. Guttural and harsh vocal styles, for example, are often described by listeners as brutal, monstrous, or demonic.'
But how we respond to sound isn't just biological—it's shaped by experience. 'Our responses to sound arise from the nervous system that broadly speaking we all have in common—but context is everything,' says Victoria Williamson, a music psychologist and co-founder of the sound wellness app Audicin. 'Some frequencies and sound textures are more difficult for the human inner ear and brain to process, a physiological clash that can trigger reactions from overstimulation to stress, disgust and even pain.'
'However,' Williamson adds, 'our psychological reaction to sound is predicated on what we have been exposed to during our lifetime and the associations we have created. That is 100 percent unique to each of us.'
Back in 17th-century Europe, that exposure was changing. While medieval music prized harmony and order, the Baroque period embraced contrast and emotion. By the Classical era, it had appeared in works by Bach, Beethoven, and Wagner, among others, often to evoke drama or darkness. In Camille Saint-Saëns's Danse Macabre, the tritone famously opens the piece with a musical scythe swing.
(Here's how Beethoven went from Napoleon's biggest fan to his worst critic.'
Since then, the 'devil's interval' has appeared everywhere—from the theme of The Simpsons to the sirens that jolt us into high alert. And in 1970, Black Sabbath picked it up again, building the haunting foundation of heavy metal on its dissonant tension.
'Black Sabbath music will trigger the deep emotion centers of the brain like the amygdala, but rather than experience fear or discomfort the listener is drawn in. In theory it makes no sense,' says Victoria Williamson. 'The more this music drives the release of emotion and stress, the more it will trigger the reward and motivation centres of the brain like the ventral tegmental area, nucleus accumbens and the prefrontal cortex. Over the years the brain will get used to the dopamine rush it gets in the presence of this music. This can help explain why Black Sabbath fans have been so intensely loyal over the decades.'