The rejection of transient and broadband gunshot noise signals in the presence of speech has the problem that speech is also transient and broadband. Although adaptive filtering and/or matched filter rejection will have some application, additional characteristics that separate gunfire from speech are needed for optimal noise cancellation. This proposal is based on those two features the difference in directions of gunfire and the talker relative to the handset microphone, and on the closer proximity of the talker relative to the sources of gunfire. These additional features are basic to the proposed approach that uses new, patented technology. This new technology, termed PrivacyFone, employs a small microphone array that emphasizes the talkers voice signal by taking advantage of the fact that the array is in the near field (acoustic induction field) of the speech and not in the near field of the gunfire. The same array also rejects signals from directions associated with the gunfire. These features, basic to PrivacyFone, provide a way to discriminate against gunfire and enhance the speech signal. Any remnant of environmental noise that remains in the transmitted signal is then further rejected by an adaptive filtering scheme.
Keywords: Radio Communications, Gunshot Sounds, Microphone Array, Artillery Fire, Pressure Gradient, Adaptive Filtering, Close Air Support, Noise Cancellation,
