Review on 20pcs Clip-on Ferrite Ring Core Black RFI EMI Noise Suppressor Cable Clip - Enhance Signal Quality and Reduce Interference by Andrew Frison

These things seem to greatly reduce background noise from overfrequency, but only in AC power cables. It produces hum on audio cables and HDMI cables seem to cause latency issues. Simply put, it cuts high frequencies best from AC power supplies or cables. For everything else, I would recommend cable management, a muffler for a specific frequency, or a crossover to cut specific frequencies completely.