Whether you call it an augmented fourth, a diminished fifth, or the diabolus in musica, the mysterious interval known as the tritone has the most complicated musical history. And the tritone is also our theme this week! It's a show we're calling "The Devil's Interval!"

Check out our dissonant playlist below:

• Camille Saint-Saëns (1835–1921), Danse Macabre – The tritone is one of the most dissonant intervals in Western music, and its undesired sound has always elicited devilish associations. It's the interval of choice that opens the violin part of Camille Saint-Saens's dark and spooky Danse Macabre. The work is based on a poem by Henri Cazalis that describes Death himself, arriving at a graveyard at midnight on Halloween, and calling forth the skeletons to dance with him and his macabre fiddle tune. That tune, naturally, features the tritone. Saint-Saens even goes one step further, deliberately mistuning the violin's E string to an E-flat, a technique known as scordatura. This scordatura turns the usually sonorous perfect fifth on the violin's open strings of A and E into a dissonant tritone of A and E-flat. It also makes the work more devilishly difficult, with one string out of tune.

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• Leonard Bernstein (1918–1990), "Maria" (and others) from West Side Story – In addition to its devilish associations, the tritone can also represent both longing and conflict. It's an interval that has a strong tendency for resolution into something more consonant. The tritone then is the perfect interval to underpin the music in West Side Story. The song "Maria," for instance, opens with a dissonant tritone that expands to a more consonant perfect fifth on the word "Maria." This is a beautiful way to represent the ongoing conflict between the Sharks and Jets being melted away by a new love. The plot of West Side Story is based loosely on the plot of Romeo And Juliet, with the Sharks and Jets being the Capulets and Montagues. Not coincidentally, in Tchaikovsky's famous Romeo and Juliet Fantasy Overture, he uses a similar tritone in the work's "love theme," representing the same conflict, longing, and resolution.

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• Claude Debussy (1862–1918), Prélude à l'après-midi d'un faune – When discussing this work, acclaimed composer and conductor Pierre Boulez referred to Debussy's Prelude to the Afternoon of a Faun as the birth of modern music.  The composition's bold use of chromaticism and unorthodox treatment of harmony becomes immediately apparent in the opening flute solo, which chromatically outlines a descending tritone. It's become one of the most famous passages in the orchestral repertoire. Although the tritone has traditionally been used to create musical tension, in Debussy's hands it becomes an otherworldly representation of the hypnotic music of a faun's pan-pipes. According to Debussy, the work was conceived as an orchestral evocation of the poem by Stéphane Mallarmé, in which a faun playing his pan-pipes alone in the woods becomes aroused by passing nymphs and naiads, pursues them unsuccessfully, and then wearily abandons himself to a sleep filled with visions.

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• Franz Liszt (1811–1886), Dante Sonata (Après une lecture du Dante, Fantasia quasi Sonata) – With its epic drama of heaven and hell, The Divine Comedy had a tremendous impact on the imaginations of Romantic artists in the nineteenth century. This 14,233-line poem tells the story of Dante's journey through the three realms of the underworld lasting from the night before Good Friday to the Wednesday after Easter. Although the "Inferno" is the part of The Divine Comedy that most people know, there are actually two more books: "Purgatory" and "Paradise." Liszt based not just one, but two large works on Dante's late-medieval masterwork: the so-called "Dante Symphony," and this single-movement piano sonata. Portions of all three books are represented in this sonata, and for the theme representing Dante's Inferno, Liszt draws heavily on the use of tritones in the opening bassline, taking advantage of their traditional association with the devil.

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• Benjamin Britten (1913–1976), War Requiem – Britten composed his War Requiem for the re-consecration of Coventry Cathedral and it was first performed there on May 30, 1962. The cathedral had been destroyed during the Battle of Britain in World War II. The piece is a clear public statement of Britten's anti-war feelings. In the opening chorus, he projects the underlying tension that caused war throughout Europe through the use of the dissonant tritone between C and F-sharp in the voices. The piece was written with three specific soloists in mind: German baritone Dietrich Fischer-Dieskau, Russian soprano Galina Vishnevskaya, and British tenor Peter Pears, symbolizing the importance of reconciliation with England's former enemies. The piece uses traditional Latin text from the Mass for the Dead interspersed with nine poems by Wilfred Owen, a World War I foot soldier and poet who was killed one week before the armistice.

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• Jean Sibelius (1865–1957), Symphony No. 4 in A minor, Op. 63: IV. Finale: Allegro – Many scholars have interpreted Sibelius' music as overtly nationalistic, often celebrating the strength of Finland during its fight for independence from Russia. His fourth symphony projects the darker side of that narrative. Written in 1911, its foreboding quality foreshadows feelings of struggle and despair that would come in full force with the start of the first World War. Sibelius creates this effect musically with the use of tritones in most of the main themes of the symphony, but this technique hits its zenith in the Finale. Sibelius creates tonal chaos by writing in both the keys of A and E-flat simultaneously, which are harmonically a tritone apart. This technique, called bitonality, forces the two keys to crunch against each other without the ability to resolve. The finale thus concludes, much like the fate of Finland at the time, in complete ambiguity.

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• Béla Bartók (1881–1945), Mikrokosmos for Piano: No. 101, Diminished Fifth – The tritone has some curious musical properties. For one, it's the rarest interval in the major scale, which makes it a bit of a pariah in traditional tonal music. At the same time, a tritone perfectly bisects an octave in two, making it somehow both discordant and strangely symmetrical and balanced. It's very weird. Many composers tried to exploit this weirdness, chief among them Hungarian composer Béla Bartók. Bartók loved the symmetry of the tritone, and features that symmetry in this Mikrokosmos piece. Bartók often went as far as equating two key centers a tritone apart as being functionally equal. Most composers, on the other hand, would see keys a tritone apart as maximally dissimilar! Bartók's appreciation of the tritone's symmetry was explained by Hungarian music theorist ErnÅ‘ Lendvai, who described Bartók's treatment of the tritone as an Axis System, referring to an "axis of symmetry."

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• Pérotin (fl. c. 1200), Viderunt Omnes (Organum for 4 Voices) – The myths surrounding the tritone are often over exaggerated. For instance, it's often stated that the tritone-the diabolus in musica-was banned by the church in Medieval times for its satanic sound. That's not entirely true. For instance, you can hear several tritones in this 13th-century religious work by Pérotin, one of the earliest known composers and a member of the so-called "Notre Dame School" of polyphony in Paris. The term diabolus in musica doesn't really show up much until the 18th-century, in works like Gradus Ad Parnassum by music theorist Johann Joseph Fux. In that work, Fux refers to the diabolus in musica as being "mi-contra-fa," that is, using the solfege syllable mi against the note fa. Mi-contra-fa does create an undesired dissonance, but that dissonance could be either a tritone or a half-step, depending on the context. And it's largely understood that Fux's diabolus in musica reference is a colorfully-worded guideline to create more beautiful music, not a religious edict.

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• Black Sabbath, "Black Sabbath" – Despite the fact that the tritone, aka "the Devil in Music," was not truly banned by the church, the rumor of the tritone being the musical embodiment of the devil has persisted in popular culture. This idea was especially intriguing for heavy metal bands who wanted to make their music sound as satanic as possible. The 1970 song "Black Sabbath" by the band Black Sabbath off of the album Black Sabbath is a perfect example. They got that name from a spooky Boris Karloff movie from the 1960s. This song is widely considered to be the first true heavy metal song, with lines like "it's the end my friend, with Satan coming round the bend." Naturally, the song is built off of an alternating G and C-sharp (a tritone) in the bass. This creates a musical foundation seemingly ordained by Beelzebub himself.