Abstract: An apparatus 10 is employed for interfacing a telephone handset 18 to a telephone network. Typically, a telephone handset has one of a variety of different microphones disposed therein, such as carbon, electret, etc., where each type of microphone has a different output level and impedance. Conversely, the telephone network with which the microphone is to be interfaced has a preselected input impedance and signal requirement intended to match only one type of microphone. The apparatus 10 includes a plurality of switches 82, 84, 86, 88 and resistors 90, 92, 94 that are manually switchable into the circuit either separately or in combination to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network. Alternatively, in a second embodiment of the instant apparatus, a variable resistor is employed to match the output impedance and signal level of the microphone with the input impedance and signal level of the telephone network.

Abstract: A method and system for radio communication between at least one parent communication unit and a plurality of slave communication units. A slave communication unit transmits an automatic answer signal in response to an incomming call receipt signal transmitted from the parent communication unit. When one of the slave communication units makes a called-person's answer to the incomming call receipt signal, it transmits a called-person's answer signal. If interference occurs between the automatic and called-person's answer signals, the parent communication unit provides a command, causing the slave communication units to stop the automatic and called-person's answer signals and permits the slave communication unit which transmits the called-person's answer signal to communicate with the parent communication unit.

Abstract: A radio telephone device consists of a base unit connected to a wire circuit and a radio telephone connected to the base unit via a radio circuit, and can perform dialing under an on-hook state from the radio telephone. In the base unit there is provided a detector for detecting a state of the wire circuit, and in the radio telephone there are provided an on-hook dialing switch for indicating on-hook dialing and a display unit for visually displaying a state of the wire circuit according to an output of the detector on the occasion of the on-hook dialing.

Abstract: Disclosed is an adaptive Finite Impulse Response ("FIR") filter speakerphone that provides improved echo cancelation by the inclusion of a tracking comb filter having nulls which change to track the voice portion of communications. The speakerphone also includes a pair of ambient noise recorders for recording both ambient background noise received from the telephone line and ambient background noise in the signal to be transmitted to the telephone line. During intervals of low signal level, pre-recorded ambient noise is substituted for the communication signals. The speakerphone also controls the respective strengths of the received and transmitted signals during intervals when voice signals are present. A delay buffer adapts the speakerphone for use in videoconferencing.