An acronym for Integrated Services Digital Network. ISDN can deliver two simultaneous connections, in any combination of data (including 2 channels of real time digital audio), voice, video, and fax, over a single phone line. Multiple devices can be attached to the line, and used as needed. ISDN uses purely digital transmission, as opposed to the analog transmission of normal telephone service. With it, you can make connections throughout the world to other ISDN equipment, such as other studios equipped with ISDN in order to conduct a long-distance recording session. If your ISDN equipment includes analog capabilities, you can also connect to analog modems, fax machines, and telephones, even though they may be connected to regular telephone service.