To use CapTel in a home or office that has a Digital Subscriber Line (DSL), you must connect to a DSL filter. The filter eliminates interference to and from the CapTel phone, allowing it to share the same line as the DSL service. Fax machines and answering machines also require DSL filters to work in a DSL environment.
Without a filter, line noises from the DSL service – such as echoes or static – can be picked up by the CapTel phone, resulting in connection problems.
The DSL filter is usually a small rectangular device that has connectors on both ends. You simply unplug the telephone line from the wall jack, insert the filter into the jack, then plug the telephone line into the filter. Typically, you’d install DSL filters on every telephone, fax machine, etc., in your home, leaving the DSL computer modem as the only unfiltered device.