This Part of IEC 60958-4 specifies the physical and electrical parameters for different media. It is one of four sub-parts that together specify an interface for the serial digital transmission of two channels of periodically sampled and linearly represented digital audio data from one transmitter to one receiver. The transport format defined in IEC 60958-1 is intended for use with shielded twisted-pair cable of conventional design over distances of up to 100 m without transmission equalization or any special equalization at the receiver and at frame rates of up to 50 kHz. Longer cable lengths and higher frame rates may be used, but with a rapidly increasing requirement for care in cable selection and possible receiver equalization or the use of active repeaters, or both. Provision is made in this standard for adapting the balanced terminals to use 75-Ohm coaxial cable, and transmission by fibre-optic cable is under consideration. The document does not cover connection to any common carrier equipment. In this interface specification, mention is made of an interface for consumer use. The two interfaces are not identical.