The acoustic signal transmission includes electrically synthesizing an audible sound signal and an insertion signal to generate a synthesized sound electrical signal at the sending side, transmitting the synthesized sound electrical signal, and extracting the insertion signal form the synthesized sound...http://www.google.fr/patents/US6947893?utm_source=gb-gplus-shareBrevet US6947893 - Acoustic signal transmission with insertion signal for machine control
Acoustic signal transmission with insertion signal for machine control
