In pro-audio terminology, a headphone amplifier is a device that allows multiple headsets to be connected to one or more audio sources (typically balanced audio sources) at the same time to monitor sounds during a recording session, either singing or playing from the "live room" or recorded tracks. Headphone amps enable singers and musicians to be able to hear other musicians who are playing in isolation booths. They also enable audio engineers and record producers to monitor a live performance or live tracking.