From the wax cylinder to the MP3 tracking global trends in music has changed a great deal over time.

In 1933, the Lomax family of ethnomusicologists and folklorists traipsed around the world with a 315-pound phonograph recorder to collect the music and stories of dozens of cultures. Today, it might be more useful to fire up YouTube or MySpace to see what bubbles up.

But the digital music revolution has also made it easier for music to cross boundaries, for trends to spread, intermingle, and evolve much faster than ever before. And musical recordings, along with many of the tools used to share and create music online have often been victim to the impermanence of the web, making the job of the modern ethnomusicologist harder than ever.

Ethan Zuckerman sat down with one such ethnomusicologist, Wayne Marshall — a blogger, DJ, and post-doctoral scholar at MIT working on a book about global youth culture and digital music — to talk about his work.