In a speakerphone device identification of signals (i.e., voice input or speaker output) in a process for reducing acoustic feedback, in a communication device, is accomplished by adding a signature noise (i.e., an identification mark) to output signals radiated by the speaker to enable these signals...http://www.google.com.tw/patents/US8045701?utm_source=gb-gplus-share專利 US8045701 - Method and apparatus for active reduction of speakerphone singing
