No return date set for a cappella singing competition

NBC is renewing its a cappella singing competition series "The Sing Off."

The network plans a return for the series, which debuted in a four-episode stint in December. The series performed solid in the ratings during a tough month for broadcast.

The network doesn't have a specific premiere date set for the return of the show, which is the latest singing-related series to get some traction on broadcast.

"Sing Off" features top a cappella groups performing popular songs in an elimination competition.