Abstract: In a telephone conference bridge, a conference port amplifier comprises amplifying means for providing signal amplification in both directions, the direction of amplification of the amplifier being switchable such that amplification can be provided selectively in one or other direction of speech transmission, while signals applied in the reverse direction are attenuated. The amplifier is biased in such a manner that, in the absence of any speech signal, the direction of amplification provided by the amplifier is from the conference bridge towards a connected telephone line, and means for detecting the presence of a speech signal applied to the amplifier for transmission from the connected telephone line to the conference bridge is arranged to cause switching of the amplifier to reverse its direction of signal amplification. By this means, the signal to noise ratio experienced by each conferee connected to the conference bridge is reduced when the silent conference bus is in the quiescent condition.

Abstract: A device for detecting the direction of speech transmission between a telephone communication device and a telephone line connected thereto comprises a detection circuit for detecting coincidence in the phase of speech signals developed across respective impedances and an impedance network by which said device is coupled to the telephone line. The detection circuit comprises a pulse generating circuit for generating trains of pulses in response to excursions of the respective signals across a reference level, and a gating circuit responsive to the coincidence of pulses of the respective trains.

Abstract: In a telephone system, compensation for transmission losses over any given section of the transmission path is achieved by inserting at a selected location in the telephone transmission path a variable gain amplifying means, sensing the amplitude of a multi-frequency tone signal received from a standard multi-frequency tone sending device located at a point in the telephone transmission path distant from said selected location, said tone sending device being adapted to emit multi-frequency tone signals within the voice frequency band at a predetermined reference level, and varying the gain of said amplifying means in accordance with the difference between the amplitude of said sensed tone signal and the said predetermined reference level.

Abstract: The invention concerns a device for use in establishing telephone conference calls, the object of the device being to enable an originating subscriber to connect a plurality of telephone exchange lines in parallel to provide a conference connection, utilizing existing telephone exchange switching facilities which do not necessarily provide for conference connections. The device comprises a so-called conference bridge, and switching means responsive to incoming command signals transmitted from a remote telephone station for connecting the remote caller either to an outlet to a telephone exchange line capable of receiving dialled switching signals for establishing a switched connection to a called party, or to an inlet port of the conference bridge.