Theories that claim music is a universal language have been proposed as far back as the ancient Greek mathematician Pythagoras. 

In the famous musical, The Sound Of Music, Maria sings: "When you sing you begin with do-re-mi." 

These three notes are the start of the diatonic scale. Combining certain notes, such as do-mi-sol, turns the sound into a harmonic chord. 

Western musicians have been preoccupied with the sounds of chords for centuries: consonant chords are perceived as beautiful or pleasant, while dissonant chords are generally used to create points of tension, which can make them sound harsh or unpleasant.

But a recent study published in Nature posits that beauty is determined by the listener.

The research examined five large-scale behavioural studies, comprising 235,440 human judgements from US and South Korean populations. 

It shows that our perception of beautiful music is shaped by the culture we grow up in, and can change as we acquire new musical experiences.

So, what's the big deal with consonance and dissonance, and what's it got to do with an ancient Greek mathematician?

Pythagoras's theory of harmony

You might remember Pythagoras and his triangle from your high school maths class, but he also theorised that beautiful harmony is a matter of calculation.

Musical chords correlate to certain mathematical ratios which make them sound appealing.

"Each note you hear is the result of a vibration," explains Professor Emery Schubert, a music researcher at the University of NSW.

"Say you play a note at 100 hertz, [the note would harmonise with another at] 200 hertz, 300 hertz and so on," Professor Schubert says.

There's one catch: although music is part of all cultures, Pythagoras's theory of harmony only works for some musical traditions, particularly a subsection of the Western harmonic tradition. The research demonstrates cultural exposure or training can change people's musical preferences.

As Professor Schubert explains, cultural influences shape our understanding of which sounds are beautiful or pleasant.

In Australia, Pythagoras's theory on harmony underpins almost all music education and music you listen to. 

Most people are exposed to this type of consonance and dissonance all their lives. You can hear it in everything from Taylor Swift's break-up ballads to Beethoven's symphonies. 

But there are millions of people around the world who live with different musical realities.

The researchers use the case study of Javanese gamelan tradition, a musical system which has very different rules to the musical building blocks you might have grown up with.

How gamelan tradition challenges  Pythagoras's harmonic calculation

One of the study's aims was to test the assumption that Pythagoras's theorem would work with any instrument, regardless of culture or geography.

The study found that in examples from non-Western cultures such as Javanese gamelan, Pythagoras's neat calculation falls apart.

Gamelan musical traditions originate in the Indonesian islands of Java and Bali, on the other side of the world from the Greek islands where Pythagoras lived.

Gamelan sets are a collection of mainly metallic instruments. In Central Java, these instruments are tuned to slendro and pelog, scales which are centuries old.

"Slendro and pelog do not map onto Western diatonic scales," says Vi King Lim, leader of Langen Suka, a gamelan group based in Sydney.

Lim describes slendro as "five notes within the octave that are equally spaced apart."

Unlike the standardised tuning most Australians are familiar with, the tunings of Javanese gamelan instruments "are very flexible between sets, depending on the [smiths who make them]," Lim explains.

In most cases, you can't easily exchange gamelan instruments from a different set like you could with a keyboard or a guitar.

Lim points out another way culture could shape musical expectations. Many people feel the pressure to sing or play in tune because this is important for people who grow up with the Western musical tradition.

But in Java, "you can sing [any song] which has diatonic tuning, accompanied by the gamelan in a different tuning and they tolerate the mismatched tunings," Lim says.

One important point the researchers make in their paper is that you don't have to be a musician to make musical judgements on what sounds beautiful to you.

But Professor Schubert says there are benefits to keep an open mind to new musical experiences, even for seasoned music-lovers.

Broadening our musical tastes might be beneficial especially in later life

"The best predictor of liking a piece of music is your previous exposure," Professor Schubert says.

Children absorb their own musical culture from a young age and that influences their preferences as they get older.