On May 13, two days before “Pitch Perfect 2” hits theaters, Northeastern University a cappella groups Pitch, Please! and the Nor’easters will appear on Pop network’s “Sing It On,” a show executive-produced by John Legend that gives viewers an inside look at a cappella ensembles. You can already check out performances by the local groups in videos on the network’s website. In related news, Pitch, Please! launched a Kickstarter campaign to fund its first album on Monday.