How does the music-identifying app Shazam work its magic?

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Oct. 19 2009 5:14 PM

That Tune, Named

How does the music-identifying app Shazam work its magic?

Shazam application logo for the iPhone.

Shazam is the closest a cell phone can come to magic. Say you're in a restaurant, a song comes on, and you can't quite place the tune. In the past, your options were limited; you could try asking your spouse or the waiter for a clue, but that approach risked revealing your ignorance. (That's " Sex Machine," dumb ass.) Shazam—which launched in the United Kingdom in 2002 as a call-in service and became widely known in the United States last year when it hit the iPhone—solves the dilemma in a few clicks. Press a button on your phone, and in seconds you'll get the artist and song title. Other than playing video games, it's the most useful thing you can do on your phone.

Last week, Shazam announced that more than 50 million people worldwide have used the service—up from 35 million at the start of the year. The company also said that it's received an undisclosed investment from the fabled Silicon Valley venture-capital firm KPCB. Shazam's success seems justified—it's the one app you can show to iPhone skeptics to get them to reconsider their position (though Shazam is also available on Android, BlackBerry, Windows Mobile, and pretty much any other phone). Yet for all the acclaim it garners, Shazam's inner workings are pretty mysterious. How does it actually ID your song? How does the company make money? (Here's one hint: iPhone users should expect to see a pay version soon.) And what are the long-term prospects for a firm whose sole purpose is satisfying an acute, very occasional need?

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First, a short explanation of how Shazam works. The company has a library of more than 8 million songs, and it has devised a technique to break down each track into a simple numeric signature—a code that is unique to each track. "The main thing here is creating a 'fingerprint' of each performance," says Andrew Fisher, Shazam's CEO. When you hold your phone up to a song you'd like to ID, Shazam turns your clip into a signature using the same method. Then it's just a matter of pattern-matching—Shazam searches its library for the code it created from your clip; when it finds that bit, it knows it's found your song.

OK, but how does Shazam make these fingerprints? As Avery Wang, Shazam's chief scientist and one of its co-founders, explained to Scientific American in 2003, the company's approach was long considered computationally impractical—there was thought to be too much information in a song to compile a simple signature. But as he wrestled with the problem, Wang had a brilliant idea: What if he ignored nearly everything in a song and focused instead on just a few relatively "intense" moments? Thus Shazam creates a spectrogram for each song in its database—a graph that plots three dimensions of music: frequency vs. amplitude vs. time. The algorithm then picks out just those points that represent the peaks of the graph—notes that contain "higher energy content" than all the other notes around it, as Wang explained in an academic paper he published to describe how Shazam works (PDF). In practice, this seems to work out to about three data points per second per song.

You'd think that ignoring nearly all of the information in a song would lead to inaccurate matches, but Shazam's fingerprinting technique is remarkably immune to disturbances—it can match songs in noisy environments over bad cell connections. Fisher says that the company has also recently found a way to match music that has been imperceptibly sped up (as club DJs sometimes do to match a specific tempo or as radio DJs do to fit in a song before an ad break). And it can tell the difference between different versions of the same song. I just tried it on three different versions of "Landslide"—the original by Fleetwood Mac and covers by the Smashing Pumpkins and the Dixie Chicks—and it nailed each one.

Fisher declined to tell me Shazam's overall hit-and-miss rate. All he would say is that the service is good enough to keep people coming back for more—the average user looks for songs eight times a month. The most common reason Shazam fails to identify a song is that it doesn't have enough data. The system needs at least five seconds of music to make a match, and sometimes people turn it on just as the song is ending. There are also frequently errors when people look up live performances—if you hold up your phone to your TV during the musical segment on Saturday Night Live, Shazam will most probably fail to ID the song. (If you do get a match from SNL, you're probably watching that episode with Ashlee Simpson—Shazam is a great way to catch lip-syncers in the act.) Fisher says that Shazam is technically capable of working on live performances, but they've turned off that ability for what he terms "business reasons." "Right now people trust the brand—trying to match live songs wouldn't get very high accuracy," he says. (If you've got a tune stuck in your head, try using Midomi, a rival of Shazam's that can ID songs based on your humming or singing.)

Shazam's iPhone version has been a blockbuster, but it still represents just 20 percent of the service's customer base, which spans more than 150 countries and pretty much every mobile carrier in the world. The iPhone version also marked a departure for the company—it was the first version that Shazam offered for free. Fisher says this proved to be a good idea; it brought Shazam instant renown, and the company now has enough of a customer base that it can make decent money through in-app ads and by getting a cut of each song purchase people make through the app. But staying fully free forever isn't sustainable, Fisher says. The company recently unveiled a Windows Mobile version of its app that operates under a "freemium" pricing model—users who download the free version can search for five songs a month, while a premium version that goes for a one-time fee of $5 will allow unlimited song searches. Fisher says that the $5 version for the iPhone (and most other platforms) will launch by the end of the year.

The company is also planning to add a lot more services to its apps—a recommendations engine, a way to let you share your musical tastes with your friends, and charts that show the songs that people are searching for. Every Monday, Shazam sends out its charts to record labels, and execs have been known to sign artists based on the data. This has led to a new way for artists to break into the mainstream: getting featured in TV ads. In 2005, for instance, Volkswagen ran an ad in Europe for the Golf GTI that featured a remixed version of "Singin' in the Rain" by Mint Royale. The song inspired a lot of searching on Shazam—and prompted the band's label to release the track, which then shot to the top of the European charts. "We probably see that at least once a month around the world," Fisher says. In other words, Shazam doesn't only help an audience find music. Sometimes it helps music find an audience.

Farhad Manjoo is a technology columnist for the New York Times and the author of True Enough.

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