Acoustic Channel

a combination of equipment and physical media for the transmission of signals by means of audio and ultrasonic phenomena. In an acoustic channel for control or inspection purposes the signals employed are either the passive type—acoustic phenomena produced by the process (usually technological) under inspection—or the active type, which are specially generated. Passive signal acoustic channels are used in industry to check the noise characteristics of manufactured products (for instance, to inspect the quality of assemblies containing gearing); in medicine they are used to study sound from an organism. Active signals in the audio or ultrasonic range are used to transmit information, make remote measurements, determine the parameters of a medium, and detect certain undesirable impurities.