What is a Tritone? Why They Call it the Devil’s Interval

The tritone is usually associated with scary, tenseful music, often used in horror film scores to create a sense of discomfort. The tritone is a fascinating phenomenon in music theory. There’s a lot to unpack when it comes to the tritone: what is it? Why do they call it the devil’s interval? Was it really banned by the catholic church?

And most importantly, why does the tritone evoke such an unsettling emotional response? 

This article explores every interesting aspect of the tritone, uncovering its history, psychology and musical mechanisms. 

What is a tritone?

The tritone is a musical interval of three whole tones (six semitones), or half a perfect octave. This means that the notes F and B are tritone combinations, as is the inverse combination of notes B and F.

It can be also be referred to as a diminished fifth or an augmented fourth, depending on the context. Because it can occur in two different places in the scale, it can also be called a double-augmented fourth or a double-diminished fifth.

What is an interval in music?

An interval refers to the difference in pitch between any two notes. For example, the interval between C2 and C5 is much greater than the interval between C2 and C3.

Since a perfect octave has the ratio 2:1, the exact frequency ratio of a tritone is the square root of 2; also written as 2(½). Here’s an example of how a tritone looks on a piano keyboard:

The sound of a tritone is considered so dissonant that it earned the nickname ‘the Devil’s interval’, and was even avoided for centuries by music composers. This nickname even went on to spark a popular myth: that the ‘Devil’s interval’ was banned in the Middle Ages by the Catholic Church.

The reason why tritones sound so dissonant is because they sit in between a perfect fourth and fifth, which conventionally are two of the most familiar sounding intervals in western tonal harmony. The tritone’s nature is often thought of as unstable and disturbing.

Here’s how a tritone sounds:

A tritone is an interval of 3 whole tones

A tritone is comprised of two notes that are 3 whole tones, or 6 semitones, apart. Or, half the perfect octave.

The perfect octave means that all the pitches are 12 steps away from each other. When you play two notes at the same time, they're an octave apart if their frequencies are exactly double one another. For example, if you play C2 and C3 together, that's an octave. 

If you play C2 and F#2 together however, it isn't, because those two notes aren't exactly twice as high as each other (they're actually 82% higher).

It can be referred to as a diminished 5th or an augmented 4th

The tritone is a six-semitone interval, and it can be referred to as a diminished 5th or an augmented 4th. Because it can occur in two different places in the scale, it can also be called a double-augmented 4th or a double-diminished 5th.

This depends on whether you're looking at it from above or below. 

Why is a tritone called the devil’s interval?

The tritone is also known as the devil’s interval. When you hear it, it sounds like something evil is happening — and you might be right!

The tritone is one of the most dissonant sounding musical intervals, which means that it doesn’t sound pleasant or smooth to the ear. The term “dissonance” comes from the Latin word for “noise” or “conflict.” Dissonance can make your ears feel uncomfortable and confused when you listen to music with these notes.

Because of its dissonance, the tritone was called "diabolus in musica" or "the devil in music" by medieval church authorities. They believed it represented Satan himself (or at least his influence). This belief continued into the 19th century, with many composers using it to signify evil characters or foreshadow impending disaster and fate!

Tritones are commonly used in horror movie soundtracks, thanks to their ability to create discomfort and tension. 

However, there are also lots of other ways that composers use tritones in their music. Some composers will use them just to add tension or a touch of dissonance to their works; others will weave them into harmonies with other notes (to create new sounds); still others will even try using microtonal tuning systems that expand beyond our standard twelve-tone system.

Why does the tritone sound so unsettling?

Some combinations of notes sound so beautiful that they make us cry, so why does the tritone sound so unsettling? It’s all just noise, right?

There’s a psychology to sound. Certain frequency combinations evoke certain emotional responses. This is largely to do with how the human brain is hardwired to detect and recognise harmony in music.

When we hear music, it is very uncommon that we hear tritones used. Our brains are accustomed to hearing harmonious musical sounds, so much that when we hear an unharmonious sound, such as a tritone, it feels unsettling and unexpected.

Professor of Music Psychology at Guildhall School of Music and Drama, John Sloboda, compares the experience of hearing a tritone to the sensation of missing the last step at the bottom of a staircase – there is an emotional sense of brief discomfort due to an unexpected encounter.

Harmonious sounds typically follow a simple frequency ratio between two notes. For example, an octave of two notes has a ratio of 2:1, producing a constant sound. Other constant intervals include the perfect 5th, which has a ratio of 3:2.

However, the tritone has a more disproportionate frequency ratio of 45:32 or 64:45. In both cases, the tritone sounds unpleasant to the human ear. Its unbalanced frequency ratio is not what we are used to. In fact, it is thought to sound so unpleasant that many emergency alarms and sirens use tritones to alert people to attention.

Examples of tritones in music

The tritone has been used by composers since at least the 17th century and continues to be used today. The tritone's dissonant sound is well-suited to various musical styles, ranging from jazz to rock and pop. Here are some examples of music where tritones are found: 

1. South Park theme song

The electric guitar riff used in the South Park theme song uses a very recognisable tritone.

2. Twilight Zone theme song

The Twilight Zone is perhaps one of the most popular examples of tritones used in music. Using a E and B flat in the melody, this theme song creates a suspenseful, spooky atmosphere.

3. Jimi Hendrix – Purple Haze

Purple Haze is introduced with tritones in its first several notes, balanced between bass and electric guitars.

4. Camille Saint-Saëns – Dance Macabre

This is another highly recognisable example of tritones used in music. You'll hear the violin flitter between a A and E-flat at around 24 seconds in.

5. The Simpsons theme song

The Simpsons has one of the most iconic intros of all time. And that's largely thanks to its energetic theme song, where pizzicato violins open the track with tritones.

It's often referred to as "the relationship between chords"

The tritone is used in a lot of chord progressions, so much so that it's often referred to as "the relationship between chords". 

For example, the chord progression G7-C7-Dm-G7 contains four chords—three major and one minor. But there's something else that stands out about these four chords: each one contains the same notes except for one note (one semitone).

The tritone is almost always used either as a root note for harmonic triads or in figures consisting of four notes where it occupies the third place after another note placed previously.

The tritone can be used as a root note for harmonic triads. The following chord progression is also based on the tritone:

1st Chord: G7 (notated "G dominant seventh")

2nd Chord: C7 (notated "C dominant seventh")

3rd Chord: Dm (notated "D minor")

4th Chord: G7 (notated "G dominant seventh")

The tritone plays an important role in music production and musical theory as a whole

In music production and theory, a tritone is an interval consisting of three whole tones. Because it's an unusual combination of notes and sounds dissonant, it's called a "dissonant interval". It has been used in music theory to describe the first movement of Beethoven's Piano Sonata No. 17 in D Minor (Opus 31), which employs this interval as part of its main theme.

Conclusion

The tritone is a very interesting and important interval. While it may seem like a bit of an oddity at first, it's actually been around since the early days of western music theory. It's used in many different musical genres and has even influenced musical styles across generations. The tritone is one of those unique intervals that can be found in nearly every genre and style of music out there!