US performance rights body SoundExchange has announced its latest partnership with a music service, designed to encourage artists to claim back-royalties. The service: Next Big Sound. The unpaid royalties? $741,000.That’s the amount that SoundExchange says Next Big Sound-registered artists haven’t claimed, anyway. The two companies are comparing lists in an effort to shift the cash, with NBS sending out emails this week to artists who are owed money, with instructions on how to claim it.It’s the latest partnership for SoundExchange, following similar agreements with MySpace and SonicBids, among others. SoundExchange has taken a fair amount of criticism in recent times over the amount of money it has collected but which remains unclaimed. It has always maintained that it’s making every effort to register artists who are owed money, though, with the NBS deal the latest example.”Next Big Sound has already confirmed the identities and contact information for thousands of artists, and has become a trusted partner for them, so when NBS says ‘You’ve got to register with SoundExchange and get your money,’ it starts to feel real to them,” says Bryan Calhoun, VP of external affairs and new media.