Noise cancellation system

A noise cancellation system for an audio system such as a mobile phone handset, or a wireless phone headset has a first input for receiving a first audio signal from one or more microphone positioned to receive ambient noise, and a second input for receiving a second audio signal from a microphone positioned to detect the user's speech, as well as a third input for receiving a third audio signal for example representing the speech of a person to whom the user is talking. A first noise cancellation block receives the first audio signal and generates a first noise cancellation signal, and this is combined with the third audio signal to form a first audio output signal. A second noise cancellation block receives at least a part of the first audio signal and said second audio signal and applying noise cancellation to generate a second audio output signal.