There are many sounds that are associated with fear, particularly in music. From the well-known funeral march chords and horror soundtracks to the single-use harp notes at the start of Camille Saint-Saëns’ ‘Danse Macabre’, identifying chilling music isn’t necessarily a difficult venture. However, one musical interval is so creepy that it’s actually been deemed the ‘Devil’s Interval’ or ‘The Devil in Music’.

When aiming to evoke a spooky ambience, contemporary pop music doesn’t exactly exist to pander to creepy undertones. Luckily, European music from earlier centuries catered to a much more chilling atmosphere than most modern music offers. In the 19th century, composers such as Franz Liszt and Richard Wagner mastered the art of eeriness with their sonic dread that comprised two crucial elements that continue to be employed by horror movies and metal bands: a forbidden sequence of notes and a haunting melody originating from songs about the end of times.

This sequence of notes, called the tritone, makes up an interval that spans three whole tones or six half steps. For instance, the notes F and B form a tritone, as do the inverse notes B and F. Alternatively termed a diminished fifth or an augmented fourth based on the musical context. It can also be known as a double-augmented fourth or a double-diminished fifth due to its occurrence in two different positions within the scale.

In traditional Western music theory, the tritone was considered highly discordant and discouraged or forbidden in certain contexts, particularly during the medieval and Renaissance periods. It was associated with tension and dissonance, contrasting the consonant and harmonious intervals more commonly used in music.

Historically, the tritone was also avoided in sacred music due to its eerie nature. This interval was believed to invoke an unsettling or demonic quality, which led to its labelling as the ‘Devil’s Interval’. This perception gradually shifted over time, and composers began utilising the tritone to introduce tension and create dramatic effects.

Perhaps one of the most interesting aspects of the ‘Devil’s Interval’ is that it doesn’t sound all that creepy at all — rather than relying on cinematic or piercing notes that evoke fear, the tritone appears more sonically unpleasant than anything else. Rather than including endearing melodic elements or rhythms that attract repeated listens, the tritone is particularly unnerving because the human brain is hardwired to find harmony and symmetry in music.

As John Sloboda, a professor of music psychology at the Guildhall School of Music and Drama, explained: “When we hear something dissonant, it gives you a little bit of an emotional frisson because it’s strange and unexpected. The emotional result of hearing a tritone might not be too different from the one experienced at the bottom of a staircase that failed to mention it’s missing its last step.”

When two notes possess frequencies with a simple ratio, they produce a harmonious blend. For instance, an octave’s ratio between two notes, resulting in a 2:1 frequency relationship, delivers such consonance that we assign both notes the same name. Following suit, the next highly consonant interval is the perfect fifth, bearing a ratio of 3:2. This pattern persists across the spectrum of intervals. The tones of the tritone, by contrast, end up in the proportion of 45:32 or 64:45. In short, this ratio sounds ugly to the human ear.

As for contemporary examples of the tritone, look no further than the theme tunes for South Park, The Simpsons, and The Twilight Zone, or check out Jimi Hendrix’s ‘Purple Haze’, or Camille Saint-Saëns’ ‘Dance Macabre’.

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