The DI4 from Alto is a 4 channel, active direct box that covers several basic functions. It can convert a high impedance signal to low impedance, convert a "hot" instrument or line level (and sometimes even speaker level) signal to a microphone level signal suitable for connection to the microphone input of a mixing console, and prevent hum and noise pick up by the use of transformer decoupling.
Housed in a rugged metal enclosure, the direct box is mains powered and is equally suitable for use on stage or in a studio environment.