The Interspace Industries PCBB3 PC is a passive Balance Box with a Hum Eliminator Jack. I/PHum can happen anywhere, power supplies, fluorescent lights, other equipment - all can cause noise that is picked up by your audio input cables! Being completely passive (no batteries or external power required) and bi-directional, the PC Balance Box can match unbalanced and balanced audio sources, line to mic levels, stereo and mono signals, and troubleshoot hum problems - all in one versatile and rugged unit. The PC Balance Box is the simplest way to interface unbalanced computer or consumer audio signals to balanced AV sound systems. The inputs and outputs are completely isolated in either direction and by using the `Ground Lift' feature where required, hum problems can be easily cured.