Would you classify Justin Bieber as pop or “pop Christmas”?

Is Arcade Fire a rock band or “permanent wave”?

How about describing Ed Sheeran as “neo mellow,” Alabama Shakes as “stomp and holler,” or the versatile Grimes as “grave wave,” “metropopolis,” “nu gaze” or all of the above?

Spotify’s “data alchemist” Glenn McDonald can proudly claim authorship of some of those eccentric descriptors. His company has used a complex algorithm to analyze and categorize upwards of 60 million songs on a molecular level — and the micro-classifications now number 1,387 sub-genres in total.

Ultimately, these machinations are allowing a new level of specificity to answer that impossible old first-date query: What kind of music are you into?

“The most interesting thing is how much music there is in the world,” McDonald said. “The number of places where I expected to find five or 10 bands and found 200 is just amazing.”

Using a tool called machine listening, songs are analyzed by Spotify’s music-intelligence division, the Echo Nest, based on their digital signatures for a number of factors, including tempo, acoustic-ness, energy, danceability, strength of the beat and emotional tone.

Taken together, those numbers can identify the distinguishing aural characteristics of different genres and regional sounds. McDonald has provided a visual representation of the subtle sonic differences at everynoise.com, which maps music along a spectrum where mechanical sounds reside at the top, organic at the bottom, atmospheric on the left and bouncy on the right.

The still-evolving tool can highlight the subtle differences in the hip hop of Quebec and Finland, for instance, or create cross-genre comparisons between such unlikely bedfellows as Thai indie and Spanish new wave. Any curiosity about what a genre called “necrogrind,” “fallen angel” or “electrofox” could possibly sound like can be satisfied by clicking on it to hear a sample.

Spotify users can take the same journey by entering “genre:” into the app’s search bar followed by any of McDonald’s colourful classifications.

The process is still imperfect. At one point, the computers confused the sound of the banjo with human singers, simply because not enough banjo samples had been entered. In another instance, Indonesian dangdut was classified as near-identical to American country because, McDonald said, the computers had no protocol to account for twang.

“(People) imagine metal humanoid robots sitting in chairs with silver headphones on nodding mechanically to songs and making up their robot minds,” said McDonald. “But the process is totally different. There’s no emotion involved. The machines are not pretending to be people.

“They’re just trying to find mathematical ways of approximating the effect that humans get from music so the scores can be intelligible and reliable.”

Once the machines have identified sonic similarities, a human touch is required to research the sub-genres or create new ones, a task that often falls to McDonald himself. It can be vexing as sub-genres are divvied into progressively tinier fractions; indie pop, for instance, has been subdivided into shiver pop, gauze pop, etherpop, indie fuzz pop, popgaze and so on.

In analyzing so much musical minutiae, McDonald has noticed that for all this century’s rampant boundary-blurring, distinctive differences still exist between types of music.

“I don’t think genres have gone away ... any more than cuisines have disappeared. There are more fusions,” he said. “So just like you can find the Korean burrito place, that doesn’t mean there aren’t also Korean restaurants and Mexican restaurants.

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“Maybe the firmness of the boundaries has gone away. It’s more possible to exist in the spaces between genres as they blend into each other.”

A look at some of Spotify’s more creative genre headings:

Catstep

Vancouver-based EDM label Monstercat is sufficiently unique that its signature sound spawned its own feline-themed subgenre. Sample artists: Draper, Mr Fijiwiji, Tristam

Deep sunset lounge

Generally, McDonald uses “deep” to narrow a genre to its most obscure outliers. In this case, the term refers to the post-party chill-out music favoured by “people in the know.” Sample artists: Ben Miller Band, the Kingston Springs, Milkdrive

Epicore

This is McDonald’s shorthand for the type of “big, booming” music that scores seemingly every movie trailer. Sample artists: Steve Jablonsky, Thomas Bergersen, Jo Blankenburg

Laboratorio

This is the music “you imagine people producing with beakers,” said McDonald, who coined the phrase after seeing Icelandic band Amiina open for Sigur Ros. Sample artists: Moondog, John Zorn, Laurie Anderson

Stomp and whittle

One of McDonald’s prouder creations, this genre is reserved for acts skewing slightly less emphatic than “stomp-and-holler” artists like the Lumineers or Alabama Shakes. Sample artists: Royal Teeth, the 1900s, Creeping Weeds