The PS4x4 PRO USB uses ARTs Advanced Power Filtering (APF). This powerful technology uses common mode and differential mode topologies in series, which minimizes unwanted noise between the AC line and ground, as well as on both sides of the AC line. The PS4x4 PRO USB purifies the electrical current that reaches your equipment, eliminating noise above 10 kHz, while attenuating noise above 100 kHz by more than 40 dB. Ground loop issues are also alleviated.