Abstract: In order to reduce acoustic echo and restore stereophonic sound in a digital transmission system of sound signals on multiple transmission channels, between a local site and one or several remote sites, comprising several microphones and loudspeakers, the method consists in the following steps: computing a weighting factor to be applied to each microphone signal before emitting, based on two attenuation factors computed from the microphone and loudspeaker signals; transmitting on each transmission channel the linear combination of weighted microphone signals; computing a weighting factor to be applied to each loudspeaker signal; and emitting on the loudspeaker the linear combination of transmitted, weighted signals.

Abstract: An acoustic antenna for computer workstation, used for video conferencing that comprises a plurality of microphones connected to a summator circuit. The microphones are distributed in a layout so as to form a substantially straight line and are each spaced with respect to a reference microphone placed in the vicinity of the vertical axis of symmetry of the screen of the workstation according to a specified law. The layout exhibits a substantially cylindrical directivity pattern whose axis of revolution is formed by the straight line.

Abstract: A system for selective sound capture for hands-free telephony and multimedia workstations of the acoustic antenna type with an aerial formed by a member with a concave cylindrical surface. The system includes a plurality of electro-acoustic transducers which are distributed over and in the vicinity of the cylindrical surface. Circuits for partial summation of a plurality of analog sound signals make it possible to form elementary acoustic antennas and a summation circuit produces a resultant analog signal representative of the sound signal arising from a useful speaking area.