200ms seems like a long time to me. From what I know, if your database takes longer than 100ms to return a query, theres something wrong[1] and CDNs have pretty much solved that "I need to get this static file around the world quickly."

With just an song id, with S3/Cloudfront and [db of choice] I don't think it would be hard to deliver a song in less than 200ms (to the continental US atleast).

[1] http://www.sqlskills.com/blogs/paul/are-io-latencies-killing... - Random article, I'm not sure where I picked it up from, but I've come to believe >100ms db latencies should be rare and when it happens, you messed up somewhere.