Berlin is alive with music at this time of year. There’s a flutist or violin player on just about every major city square, entertaining passersby and hoping, of course, to earn a penny or two. They may not be aware of it, but they're practicing a tradition that goes back for centuries. In the middle ages, carolers went from house to house, singing in return for food, drink or alms. In England, wassailing - as it became known - could get pretty wild and the Puritans banned it altogether. But that was short-lived and today's street musicians are usually less interested in causing a ruckus than in making urban life a little more harmonious.