Diving into the science behind consonance and dissonance in music

By Mia Costales

You watch as the actress cracks open the basement door. The camera pans down, revealing rickety wooden stairs leading to a pitch black abyss. As she descends down the steps, the soundtrack swells. The boom of timpani grows louder, mimicking the sound of a human heartbeat. The sharp shrill of violin strings send an involuntary chill down your spine. As the tempo picks up, you notice your pulse is steadily rising as well. Then, BOOM. A cacophony of noise blares through the speakers as a monster emerges from the dark. You may not have noticed, but that feeling of impending dread is thanks to the music. 

Music is a unique medium in that it has the power to replicate human emotion through sound. Music can influence mood, trigger memories and even shape emotional responses to experiences. To many, music in minor keys evokes feelings of sadness, longing and exhaustion. Major keys may evoke feelings of joy, jubilation and excitement. Music theory, the study of the fundamental elements of music — such as notation, rhythm and form — can offer scientific explanations as to why we associate particular sounds with emotions. 

Michael Fabian, a music professor at Cal Poly Humboldt, explained that in Western cultures, certain elements of music can sound consonant or dissonant. Typically, Western music that is considered consonant has a neutral or pleasing quality to it. On the other hand, dissonance is characterized by tension or unpleasantness.      

“Western music uses a tuning system based on ratios,” Fabian said. “The closer the ratio, the more dissonant the sound. There is an argument about the mathematical purity of the ratios being more ‘naturally’ pleasing to our ears, but that is a trend and not a guarantee.”

These ratios are also known as intervals. Intervals are the tonal distance between two notes. The term ratio concerns the proportional relationship of the frequencies of the sound waves between any two notes. The further apart each note’s sound wave frequency is from one another, the more pleasing to the ear it sounds.

In music theory, an interval such as a perfect fifth, is considered very consonant because the distance between each note is seven half steps — half steps being the smallest interval between two notes in Western music. Thus, the distance between each note’s sound wave  frequency is further apart. A popular example of a perfect fifth is the jump between the notes in the first two “twinkles” and the notes in the second two “twinkles” in Twinkle Twinkle Little Star. 

Conversely, a minor second interval, which sounds tense, only contains one half step, making it sound dissonant. This is because the distance between each note’s sound wave frequency is much closer together. An example of a half-step is the difference in tone between an F# key on a piano, which is a black key, to the G key, the white key directly next to the black key.

The tempo, or speed, at which music is played also plays a large part in evoking human emotion. Rebekka Lopez, a 2023 music performance graduate, shared how she believes the tempo can affect the way a listener absorbs music. 

“The same exact melody can be played at different tempos and have a completely different effect on the listener depending on that,” Lopez said. “Even a super ‘happy’ melody can sound nostalgic or pensive if it’s performed more slowly. Vice versa, a normally slow melody can be sped up and take on a different meaning. As humans, we all experience higher heart rates for anxiety, excitement, fear and happiness, and much slower heart rates for calm, tired, empty, depressive and pensive moments.”

While elements like tempo, dynamics or phrasing definitely contribute to how a listener interprets the music, it’s important to note that no two people hear a piece of music exactly the same. Cultural, geographic and even generational differences hugely factor into how a person perceives music and what they perceive as ‘good’ or bad.’ For example, a 2016 study conducted by MIT and Brandeis University found that Westerners considered the interval between the notes C and F#, known as an augmented fourth, to be very dissonant, while members of the Tsimane’ tribe found the chord pleasing to the ear. 

“It’s crucial to remember that our perception of sound and music is hugely influenced by the musical culture we grow up listening to,” Fabian said. “To many people in my class, songs in minor keys sound ominous, tritones sound dissonant, et cetera. But for others, minor sounds melancholy, and tritones sound energetic. It really has so much to do with the music you heard growing up.”