A new adaptive filter is presented and its analytical and simulation studies are described. It requires no previous knowledge about the nature of its inputs. The only assumption is that the power spectral density of the signal component of an input x(t) is concentrated in a relatively narrow frequency band, and that of the input has its absolute peak in this frequency range. The device consists of a delay-line synthesiser with time-variable weights and a set of controllers. The synthesiser gives an output
y(t)=^2lΣ_μ=0v_μ(t)x(t-μΔt)+cx(t-lΔt)
where v_μ(t) are time-variable weights, c is a constant weight and Δt is a delay time between taps. Each controller adjusts one weight for adaptation according to the following equation
Tdv_μ(t)/dt+v_μ(t)=x(t-μΔt)sgn[y(t)].
It can be shown that after sufficient length of time a suitable band-pass frequency characteristic for the extraction of the signal component is obtained. Initial values for v_μ(t) are arbitrary. The analytical results are verified by some simulation studies on a digital computer.