A first major aspect of the invention relates to an active noise cancelling system which detects (4) ambient noise and applies electro-accoustic processing (8, 9) thereto (3) to produce an acoustic signal for cancelling out the ambient noise. The active noise cancelling system may be used to cancel all noise but an audio signal (12) which is desired to be heard by the user. A second major aspect of the invention relates particularly to a system for electronically cancelling noise input to a user microphone, by utilizing known characteristics of speech signal and ambient noise. The first major aspect of the invention can be used in concert with the second major aspect in a communication system at the earpiece of a telephone and the mouthpiece of a telephone.
