“Ninety-nine percent of what I do is on the computer,” he says. His studio in Malmö, Sweden, consists of little more than keyboards, virtual instruments, and software. Holmström now composes full-time for King Digital Entertainment, which develops easy-to-play, impossible-to-put-down games for mobile devices and the web. (“Casual” games are the sort you play for a few minutes on the subway, or waiting in line.) If the sequel continues to succeed on mobile devices and online, Holmström's composition will deliver the London Symphony Orchestra to low-fi laptop speakers and iPhone earbuds across the world. Candy Crush Soda Saga is the sequel to one of the most successful casual games ever, King Digital Entertainment's Candy Crush Saga, which was downloaded half a billion times. In an era of shrinking audiences for classical music, performers and composers have found an unlikely ally in the simplest and cheapest kinds of video games. Its composer, Johan Holmström, has created the music for more than a dozen popular games.

But a few months ago, the London Symphony Orchestra performed music that's popular on a entirely different platform: the soundtrack for the video game Candy Crush Soda Saga.

It's where the Beatles recorded “A Hard Day's Night” and “Revolver,” and where John Williams conducted the stirring themes of the Star Wars films. Abbey Road Studios in London has heard more than its share of memorable music.