Patent Document ID: 8199923
Application ID: 12015219
Patent Flag: 1

Claim One:
1. A system for active control of an unwanted noise signal at a listening site radiated by a noise source where the unwanted noise is transmitted to the listening site via a primary path having a primary path transfer function, the system comprising: a loudspeaker for radiating a cancellation signal to attenuate the unwanted noise signal, where the cancellation signal is transmitted from the loudspeaker to the listening site via a secondary path; an microphone at the listening site for determining through an error signal the level of achieved reduction; a first adaptive filter for generating the canceling signal by filtering a signal representative of the unwanted noise signal with a transfer function adapted to the primary path transfer function using the signal representative of the unwanted noise signal and the error signal from the microphone; and a reference generator for generating a reference signal which is supplied to the loudspeaker together with the canceling signal from the first adaptive filter, where the reference signal has at least one of an amplitude and a frequency such that the reference signal is masked for a human listener at the listening site by a wanted signal present at the listening site.