Shields unused phono (RCA) sockets on audio equipment from high RF noise(/300MHz to above 1GHz) now commonly inundating homes - coming from mobile phones modern PCs USP wiring 'Bluetooth' (wireless and cordless data connections) etc. Why? High RF can enter open sockets. Once waves enter (or merely impinge on the socket's inner 'live'/'hot' terminal) they are capable of spreading quite readily all over the 'insides' the equipment. The effect was described by one astute HFN/RR reader as 'systemic'. The RF is not conducive to the equipment's correct operation hence degrades audio quality.