Spotify's Secret Weapon

D.A. Wallach (left) is Spotify's secret weapon.

When D.A. Wallach set out to tour the U.K. as one half of the indie pop duo Chester French, he wasn't quite sure what to expect from city to city. Sure enough, there were some early surprises–in Manchester, a few hundred people showed up; in Bristol, there were only two.

"I've got tons of love for Bristol and for the two people that showed up," he says, peering through a pair of fashionably over-sized spectacles over lunch in Manhattan. "But that ...