Convert the Output of Unbalanced Devices. Professional Power A direct box, or DI box, provides the facility for the direct insertion of an audio signal into a mixer or recorder. The PDC21 offers a variety of DI solutions for live sound and recording applications. You can connect all kinds of audio signals like guitars, keyboards, outboard signal processors and even high-powered speaker output from an amplifier. This unit enables you to tap off the signal from a guitar or bass guitar and pass the signal from the Para Output to the on stage amplifier without affecting the original sound. This can eliminate the need for mixing the guitar amplifier, which in many cases is preferable, especially with bass guitar.