By: Abi Kirubarajan

From Caribbean reggae to Indian raga, almost all music uses higher pitches for melodies while bass-ranged instruments manage the rhythm. Laurel Trainor, Director of McMaster’s Institute for Music and the Mind, set out to discover why this happens and what this means for music as a whole.

Her team analyzed how humans detect rhythm through observing individuals exposed to offbeat music. In the experiment, her colleagues played both high and low pitched piano notes to over thirty subjects. Occasionally, the notes were played offbeat by only fifty milliseconds. The majority of individuals were able to detect the offbeat rhythm more often in the lower tone, in comparison to the higher tone. Next, her colleagues asked the subjects to tap their fingers along to the beat of the tonal sequences. Again, when the offbeat timing occurred, the individuals were more aware of the lower piano notes and adjusted their finger tapping accordingly.

The researchers also measured the subjects’ electroencephalography activity during the experiment. Electrical activity in the auditory cortex increased significantly in response to the offbeat low notes. To confirm their results, the researchers ran the tonal sequences through a computerized model of the ear, whose output correlated with the neural activity in the auditory nerve. The simulation also demonstrated heightened neural activity during the timing errors of the lower musical notes, in comparison to the higher notes.

“Virtually all people will respond more to the beat when it is carried by lower-pitched instruments,” Trainor said.This research suggests that it is easier for listeners to discern rhythms in deeper bass notes, providing a physio- logical foundation to music.

Today’s music industry makes the most out of this phenomenon. While a prominent bass is prevalent across multiple music genres, this is most evident in electronic dance music and dubstep. Ultimately, it is the bass rhythm that compels listeners to follow along to the beat. The bass “drop” refers to the point in the track at which a switch of the bass line occurs, thus changing the rhythm of the song. Our ears are so sensitive to slight shifts in bass rhythms that a recognizable build of tension usually precedes a bass drop.

“There is a physiological basis for why we create music the way we do,” said Trainor.

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