Presenting the 4×4 PRO USB SERIES Power Distribution Systems from ART. Built on the foundation of the popular 4x4s, the PRO USB SERIES are durably constructed, reliable power conditioners for use in many applications. Wherever power management system is required, the 4×4 PRO USB SERIES provide the surge protection you need to keep your rack safe from unwanted disruption. All PRO USB SERIES models have an additional internal discrete module called APF (Advanced Power Filtering) which filters out digital and dimmer hash as well as any high frequency noise that is above the audio range. Some off-the-shelf add-on modules saturate and lose their filtering effectiveness as the loadincreases, but by using a high power discrete design we were able to create a filter that stays effective over the full operating range.