A DSL filter stands for Digital Line Subscriber filter which is an analog device and improves the minimizing telephone signal interference with the DSL system. This DSL filter exists like a very small rectangular device connected with RJ11 connectors. When a DSL filter is installed, it acts as a barrier and prevents the interference of low frequency telephone signals with high frequency ADSL system. These Filters restrict the problem of Line noise. It is a type of adapter only that fits into a jack. This filter is needed by each and every device such as phone, fax, dial-up Modem or other devices which are sharing the phone line that has DSL services as it removes hiss from the line which slows down the performance.