The Audio Quest USB (Universal Serial Bus) Input / Output Noise Stopper Caps are a pack of caps which fit over unused USB (Universal Serial Bus) inputs or outputs. Their function is to prevent electromagnetic/radio-frequency interference (EMI/RFI) from entering your system. This can cause unwanted noise & reduce the clarity & quality of your listening experience. Fortunately these can help reduce this interference & increase your enjoyment of your music. They also help prevent dust & dirt from entering the socket.