A method for controlling a voice-controlled voice direction recognition unit for a digital telephone station, which can be connected to termination units having different hybrid attenuations. The method prevents self-interruption in the transmission side due to an excessively low hybrid attenuation....http://www.google.com.hk/patents/US5048082?utm_source=gb-gplus-share專利 US5048082 - Voice direction recognition in a digital telephone station
