Adaptive Interference (Noise) Cancellation **new** 2003/07/09 16:47:56.213 GMT-5 2004/02/19 09:56:50.153 US/Central Douglas L. Jones dl-jones@uiuc.edu Douglas L. Jones dl-jones@uiuc.edu Kyle Clarkson kclarks@rice.edu adaptive noise cancellation adaptive noise canceller adaptive interference cancellation adaptive interference canceller Adaptive interference (or noise) cancellers are widely used. An adaptive noise canceller adaptively filters a noise reference input to maximally match and subtract out noise or interference from the primary (signal plus noise) input. Automatically eliminate unwanted interference in a signal.

The object is to subtract out as much of the noise as possible. Engine noise cancellation in automobiles

The firewall attenuates and filters the noise reaching the listener's ear, so it is not the same as n k ' . There is also a delay due to acoustic propagation in the air. For maximal cancellation, an adaptive filter is thus needed to make n k ' as similar as possible to the delayed n k .

What conditions must we impose upon the microphone locations for this to work? (Think causality and physics!)

Analysis of the interference cancellor

ε k 2 s k n k y k 2 s k 2 2 s k n k y k n k y k 2 We assume s k , n k , and n k ' are zero-mean signals, and that s k is independent of n k and n k ' . Then s k n k y k s k n k y k 0 ε k 2 s k 2 n k y k 2 Since the input signal has no information about s k in it, minimizing ε k 2 can only affect the second term, which is the standard Wiener filtering problem, with solution W R n ' n ' P n n '