DSL filters are also referred to as micro-filters. It is a small, rectangular in-line device with phone connections on both its ends. When used in the DSL setup, the telephone line is unplugged from the wall jack and the DSL filter into the wall connection instead. The telephone line that was unplugged from the wall jack is inserted into the other, vacant end of the filter.
DSL filters are not only used when the DSL and phone service share the same line, but also used with fax machines and answering machines.
DSL filter functions by separating the data signals and voice that is sent through the phone lines with the intention of ensuring that the two signals do not interfere with each other. If they are allowed to interfere, not only is the DSL service affected negatively, the telephone reception is full of noise as well. It becomes next to impossible for a person to navigate the Internet and talk on the phone at the same time.
DSL filters are not always used when installing DSL service. The requirement of the device is determined by the use of splitter in the main telephone cable. If the splitter has been used in the telephone cable, two lines emerge from it. One of these lines is used exclusively for the telephone equipment, while the other is used completely for the DSL modem. This eliminates the need for a DSL filter. However, if there is no splitter, then a DSL filter is required to keep the voice and data signals separated.
There are some equipment that come with an in-built filter. Therefore, they do not require the use of a DSL filter.