An improved noise cancelling apparatus is disclosed combining a unique directional noise cancelling microphone structure with a noise reducing, signal shaping electronic circuit. The microphone structure simultaneously receives two input signals; a first signal containing only ambient noise and a second...http://www.google.fr/patents/US5239578?utm_source=gb-gplus-shareBrevet US5239578 - Noise cancelling apparatus for a telephone handset
Noise cancelling apparatus for a telephone handset
