A CDJ is a specialized digital music player for DJing. Originally designed to play music from compact discs, many CDJs can play digital music files stored on USB flash drives or SD cards. Unlike consumer CD players, CDJs use high quality digital-to-analog converters. In typical use, at least two CDJs are plugged into a DJ mixer. Many CDJs have jog wheels and pitch faders that allow manipulation of the digital music file similar to a vinyl record on a DJ turntable. Some CDJs have additional features such as loops and beat analysis that are not possible with turntables. Some CDJs can also be used as DJ controllers to control the playback of digital files in DJ software running on a laptop instead of playing the files on the CDJ.