19-05-2025
Why is Japan's earthquake alert chime scary? Composer shares sound's science
TOKYO -- When an earthquake measuring a lower 5 or stronger on the 7-point Japanese seismic intensity scale is predicted, public broadcaster NHK airs an emergency earthquake alert chime on TV and radio, known for its distinctive melody. Even in noisy environments, this sound is clear and can evoke a sense of fear. But why is that?
The chime was created by Tohru Ifukube, 79, professor emeritus at the University of Tokyo who specializes in welfare engineering. He is also the nephew of the late Akira Ifukube, renowned for composing the main theme of the movie "Godzilla."
According to Ifukube, the alert chime uses a melody where the pitch changes rapidly in a short period. Sound travels as vibrations, which are converted into electrical signals in the inner ear and sent to the brain. This process allows the brain to extract changes in sound, making the chime easy to hear even amid background noise or when hearing ability is diminished. Such sounds with rapid frequency modulation are known as "FM sounds," and natural examples include babies' cries and the calls female monkeys use to attract males. "Among mammals, FM sounds act as stimuli to signal danger," Ifukube explains.
NHK commissioned Ifukube to create the chime in 2007, with the core requirements being that the listener feel a sense of urgency, that it wouldn't induce discomfort or anxiety, that it be audible in noisy environments, and even by those with mild hearing impairments. Searching for a melody that met these criteria, he hit upon his graduate research on FM sounds.
"Rather than a buzzer sound, I want music that carries a message," Ifukube thought. His attention then turned to the first chord of the third movement of his uncle Akira's symphony "Sinfonia Tapkaara." By changing the key, the chord's notes became "C, E, G, B-flat, D-sharp." The D-sharp added tension, so he decided to make this chord the base of the chime.
The final selection was narrowed down to five candidates, and an evaluation experiment was conducted with 19 participants, including those with congenital severe hearing loss, age-related hearing loss, children and adults. The current chime, which includes dissonance, was chosen.
"Tapkaara" in the Ainu language means "stand up and dance." Ifukube remarked, "Stand up and evacuate. It was a perfect fit for the chime,"
(Japanese original by Mai Suganuma, Lifestyle, Science & Environment News Department)
