A clear, high quality voice signal with a high signal-to-noise ratio is achieved by use of an adaptive noise reduction scheme with two microphones in close proximity. The method includes the use of two omini directional microphones in a highly directional mode, and then applying an adaptive noise cancellation...http://www.google.co.uk/patents/US7817808?utm_source=gb-gplus-sharePatent US7817808 - Dual adaptive structure for speech enhancement
