Q: Why do I need to use a filter on my DSL line? What is the difference between a filter and a splitter?A: Filters are used to ensure voice quality on lines that have both voice and data service on them. Lines that do not have filters on them are likely to contain static and can interfere with the performance of your data service.A filter only has one port, and would be positioned between your wall jack and your phone. A splitter has two ports, and therefore can accommodate both your phone and your DSL modem, for those that prefer to have their modem and phone in the same location.