Block diagram of adaptive filter. The reference noise x(n) is passed through a delay line (represented by Z blocks). The tap-weights (w
(n)) multiply the delayed x(n − i), which are summed to form y(n). Because y(n) approaches the true noise in d(n), the difference between them ε(n) form the output with the noise cancelled. The adaptive algorithm (LMS or RLS) regulates w
(n) based on ε(n).