The model 47 is designed to interface 2-wire full-duplex party-line intercom circuits with 4-wire audio circuits associated with matrix intercom systems. Other specialized audio system interfacing applications can also be supported. The Model 47 provides two independent full-featured 2-channel interfaces. Each interface contains two hybrid circuits which include automatic nulling capability. The analog circuitry, under software control, provides excellent audio quality and high return-loss. The interfaces are compatible with powered and unpowered 2-wire party-line circuits. They are capable of supplying DC power to devices such as user belt packs and user stations. Independent power sources are provided for both channels (pins 2 and 4) of each interface, allowing direct support for broadcast source assignment panel (SAP) applications. Configuration settings allow the 2-wire and 4-wire interface circuitry to be compatible with a range of nominal signal levels. Audio level meters provide user confirmation of system performance during setup and operation. Applications for the Model 47 include mobile and fixed television facilities, them park and theater installations, and industrial testing environments. Standard audio connectors are used for all input and output signals. The Model 47 mounts in one space (1RU) of a standard 19" rack enclosure and requires 100V-240V, 50/60Hz for operation.