Abstract: A training signal is supplied to an echo canceller of a voice conference system and the echo canceller is trained in response to the training signal. The training signal is supplied to the canceller only at the turning on of the power supply to the voice conference system. The results of the training are held after the training is completed.

Abstract: A method for training an echo canceller of a voice conference system, to cancel an echo by subtracting an estimated echo signal from an actual echo signal, includes the steps of: generating, at a time of a first training session, an initial echo signal and an initial training signal through feeding of a training signal to a loudspeaker and to the echo canceller; obtaining a response characteristic of the echo canceller to the echo signals; storing the initial echo signal and the initial training signal; and training the echo canceller, during subsequent training sessions, by using the stored initial echo signal and the stored training signal.

Abstract: A voice conference system using echo cancelers. The system consists of at least two microphone to send out voice signals to a remote location, and a loudspeaker which receives in voice signals from the remote location. To prevent the microphone from picking up the loudspeaker sound, each microphone is hooked to the separate terminal of a comparator. Thus the a person's voice in one microphone will pass, but the loudspeaker sound being received equally by both microphones will be cancelled.

Abstract: A teleconference system comprises a plurality of microphones and a plurality of expanders connected respectively thereto for expanding the outputs of the microphones. A summing ammplifier produces a sum of the output signals of the expanders and feeds a compressor to compress the sum for transmission to a distant conference location. A desired signal from a given microphone has a higher level than undesired signals which may be detected by adjacent microphones, so it is emphasized by the associated expander with respect to the undesired signals. The compressor provides compression of the high- and low-level components of the sum in equal proportions so that the former is converted to a replica of the desired signal and the latter is suppressed to acceptable levels.

Abstract: An audio bridge for a telephone conference is disclosed. The audio bridge; comprises a channel signal processing unit assigned to at least three channels. Each channel signal processing circuit comprises an echo canceller to cancel an echo signal from the transmitting side fed back to the receiving side, an amplifier and attenuator circuits to adjust levels of an output of the echo canceller and a transmitting signal transmitted through the channel signal processing circuit, an ERL determining circuit to determine an echo cancellation on the basis of the output from the echo canceller and a signal level on the transmitting side, and a gain/loss computing circuit to compute a loss in a predominant voice condition and a gain and a loss in an inferior voice condition.