If you currently have internet service with one of the many DSL companies in your town, chances are that your phone line has some kind of DSL filter. This filter from DSL providers is crucial, as it prevents interference with signals in other frequencies when you are using the internet. Without it, your connection can experience major performance issues and slowdowns. You can prevent these issues if your DSL internet and phone line are separated. But if you currently have a filter, it’s probably of the analog, low-pass variety. If you want to learn more about which kind of filter a particular DSL company you’re interested in uses, you can either check their website for technical information, or get talk to a representative over the phone.