The screech of a dissonant violin, a ghostly whisper, a cry in the night, a sinister laugh, a distant rumble, a howling wind. These unsettling sounds are the stuff of horror films and haunted houses. They can make our blood run cold.
Why is it that though they are only vibrations, some sounds can make our hearts beat faster and our hair stand on end? How do they evoke the terror of unseen danger lurking just behind us?
Psychoacoustics can help us see (or hear) the reasons more clearly. This discipline at the intersection of physics and psychology, which studies how sound waves are received by our auditory system and interpreted by our brains, is among the interests of , a professor in the Faculty of Music at Universit茅 de Montr茅al.
A unique 鈥渃olour鈥� of sound
Traube, a musician and engineer by training, explained that psychoacoustics measures a sound鈥檚 timbre or quality on a scale of bright to dark. A joyful sound is generally 鈥渂right,鈥� energetic, harmonious and richer in the high frequencies. However, if the timbre is more dissonant, high frequencies can also arouse fear or terror because of their resemblance to human screams.
Evoking emotions through sound
In psychology, emotions can be plotted along two axes: level of physiological arousal and valence (the positive or negative nature of the emotion). For instance, joy typically has a positive valence and high arousal, while sadness has a negative valence and lower arousal.
The modulation of sound in music is similar to the way the human voice modulates to express emotion. 鈥淢usic can therefore convey emotion by mimicking the acoustic characteristics of affective human vocalizations,鈥� said Traube. 鈥淪tudies have shown that scary movie soundtracks often have a shrill quality, which is a naturally alarming tone.鈥�
One example is the aggressive violin bow strokes over a dissonant high chord in the famous in Hitchcock鈥檚 Psycho.
Deep, ominous sounds
Darker, rougher timbres in the lower frequencies can also provoke fear. 鈥淭hese sounds are more like a growl, something big and cavernous,鈥� said Traube.
These types of low frequencies can be intimidating, creating a sense of something fearsome lying in wait, since the pitch of a sound determines our impression of size.
鈥淲e perceive high-pitched sounds as small and dense, while low-pitched sounds are perceived as wide and voluminous,鈥� Traube explained. 鈥淚t鈥檚 no coincidence that the deep tones of cellos and double basses are used to evoke a large, threatening shark in the opening sequence of Jaws.鈥�
Strange and ghostly sounds
In a different register, sounds produced by a theremin鈥攐ne of the earliest electronic instruments, played without physical contact鈥攁re often used to evoke the eeriness of haunted houses and the strangeness of aliens in sci-fi films(see video).
鈥淭he electronic timbre of the theremin is pure but voice-like,鈥� Traube noted. 鈥淚ts distinctive feature is the particular modulation of pitch to create intonation contours that resemble a human lament.鈥�
This similarity signals to the brain a potential danger to self and also to others. In this case, the feeling of fear is produced by empathy, or 鈥渆motional contagion.鈥�
So whether they suggest a menacing growl or a cry of anguish, sounds can scare us because they trigger a primal response, a kind of defence mechanism against threats.
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