It began with an argument. Tristan Jehan and Brian Whitman met as Ph.D. candidates at MIT’s Media Lab. Both were amateur musicians passionate about the ways technology might recommend songs based on a listener’s tastes. Both were convinced that “collaborative filtering,” a trendy means of achieving that goal, was woefully inadequate. Their disagreement? Jehan’s research focused on teaching computers to capture the sonic elements of music, while Whitman’s studied the cultural and social components. In combining the two approaches they created the Echo Nest, one of the most important digital music companies few have heard about.