Patent ID: 8908876

Claim:
An ambient noise cancellation system, comprising: an input for a digital signal representing ambient noise, the digital signal having a first sample rate; a digital filter, connected to the input to receive the digital signal at the first sample rate; a decimator, connected to the input to receive the digital signal at the first sample rate and to generate a decimated signal at a second sample rate lower than the first sample rate; and a processor, wherein the processor comprises: a source input, for receiving a wanted signal; an emulation of the digital filter, connected to receive the decimated signal at the second sample rate and to generate an emulated filter output; an adder, for forming a sum of the emulated filter output and the wanted signal; and a control circuit, for generating a control signal on the basis of a comparison between said sum of the emulated filter output and the wanted signal and a threshold value, wherein the control signal is applied to the digital filter to control a filter characteristic thereof.