A cappella is a unique style - vocal harmony without musical accompaniment. Today, it is more than a traditional barbershop quartet with four male voices. There are all male, all female and co-ed groups, each tackling a variety of musical styles from childhood favorites to top 40 hits

In an age of electronically produced beats, the music scene at American colleges has an unlikely favorite. A cappella concerts are being held on campuses around the country, and many are sold out, packed tighter than sporting events.  Kate Moody reports for VOA from Georgetown University in Washington.