An Improved Method of Noise Rejection
The effectiveness of conventional noise cancellation techniques is limited by tolerances between the signal path and noise path A system is described in which the ambient noise error signal is fed back for further cancellation (Advanced ambient Noise Rejection Technology, ANRT). Two microphones slightly separated differentiate near field signals from high level ambient noise. Band limiting filters further reduce high frequency phase distortion. The effectiveness is increased such that an unintelligible signal produced by normal speech can result in a SNR improvement of 40 dB in an ambient noise field of 98 dBA. The technology can be integrated into a single, small low power CMOS analogue integrated circuit; it is also ideally suited for MEMS (Si-Mic).
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