Why lower notes hold the key to rhythm

Turns out the bass is the driving force in music for a reason.

Each song may have its own unique sonic fingerprint, but researchers see a common thread running through nearly all music.

“One of the things about music composed around the world is that the higher-pitched instruments tend to carry the melody line, and the lower-pitched instruments tend to lay down the rhythm,” says neuroscientist Laurel Trainor of the McMaster Institute for Music and the Mind in Ontario.

From the grooves of Fela Kuti to the pop of Pharrell to the salsa swing of Celia Cruz, music across continents and centuries share this same characteristic. It may seem an obvious structure, with an obvious explanation: it’s just the way that a song sounds best.

But Trainor wanted to do an experiment to figure out why. What’s happening in our bodies that tells us its good to arrange music this way?

So she had 17 participants come into her laboratory, where each donned an electroencephalography (EEG) measuring device. It has all the glamour of a hair net dotted with electrodes, but it offers scientists a window into the brain’s reaction to sounds.

Trainor and her team then played two piano notes, a G below middle C, and a B flat, an octave and a bit above that, over and over again. Every few beats, either the higher note or the lower note was played 50 milliseconds out of rhythm, a barely perceptible shift.

“What we [were] interested in knowing is, if we change one of the timings of those notes, is your brain going to respond more if we change the timing of the low note, or is it going to respond more if we change the timing of the high note?”

That is, which mistakes in the rhythm does the brain react more strongly toward when played off beat?

The answer was pretty clear.

“The brain responded more when we changed the timing of the low note than when we changed the timing of the high notes,” says Trainor. “And that is probably why we put the rhythm in the lower pitched instruments, because our brains are just better at picking up that timing information.”

These results were recently published in the Proceedings of the National Academy of Sciences.

Connecting results with early survival mechanisms 

Trainor and her colleagues also played the same off-beat piano sounds through a computer model of the ear. It was right there, within the inner ear—in the cochlea—where the response originated, suggesting our bodies are built to hear like this. It isn’t just something we grow used to through repetition.

“It is less of a function of learning,” says Trainor. “It is not just that we’ve listened to a lot of music with the bass carrying out the rhythmic function, but it is actually in the physiology of our ear that we hear that way.”

She offers a theory for why humans evolved this way, and it has little to do with music. Picture our early ancestors, out alone in the woods. Hearing was about survival, about hunting, and being hunted, and protecting the young.

“It really evolved in order to figure out what objects are in the environment, and where they are located,” she says.

Higher pitched noises, like a baby’s cry or an animal’s call, are placed at a premium. The lower sounds add an additional layer of information: not just what something is, but where it is. Is it coming closer, or retreating?

Today, the way we hear music may be a direct result of that early survival mechanism.

The scaffolding of song

Songwriters may not be aware of the complicated science of rhythm, but they’ve understood its power dating back centuries.

David Ludwig is a classical musical composer and instructor at Philadelphia’s Curtis Institute of Music. He says his own original music doesn’t stem from a rigid starting point.

“Creativity really comes from the unconscious mind. There is not a lot of order up there, and things just kind of pop in. And if you are lucky enough to receive it, you just jot it down. So sometimes it is a bass line, sometimes it is a melody, sometimes it is a sound, sometimes it is a topic,” says Ludwig.

He points to one of the most famous 19th-century composers, Frederick Chopin, as someone who mastered the balance between rhythm and melody.

One of Ludwig’s students, George Fu, joins us in his office to play a Chopin work called “Polonaise in F-sharp Minor, Opus 44.”

But instead of playing it as written, Fu first plays it with his left hand much farther over to the right side on the piano, much closer to his right hand, shifting the rhythm out of the lower tones.

The result is thin, not quite shrill, but fleeting music that holds no power over the ear.

Ludwig then instructs Fu to play the opus as Chopin wrote it, with this rich lower section propelling the piece forward.

“I think it just hits you in the gut, really,” says Ludwig over the resonance of the piano. “It reaches out and grabs you, that rhythm. And you hear it so much more strongly because it is in the lower end of our hearing.”

Ludwig and Professor Laurel Trainor both say that for music to really catch in your ear, whether its a classical piece or Top 40, it needs both the lows and the highs working together.

The bass, when done right, is like scaffolding for the melody, holding it up, letting it soar. Even if it’s often not the most memorable part of a song, without the rhythm, the song probably wouldn’t be worth remembering.