The isolation of undistorted sinusoids in real time

A single-input, multiple-output adaptive filter that takes a multisinusoidal input signal and produces the individual sinusoids at each of the outputs is described. The individual outputs have identical amplitudes and phases to the components of the original input signal. The filter can be adapted in real time using approximate Gauss-Newton updates without requiring any matrix operations or divisions. The filter is an extension of a cascade adaptive IIR (infinite impulse response) notch filter reported previously. The filter is very amenable to being realized using custom ICs or DSP (digital signal processing) ICs, as no divisions are required and most of the filter is composed of identical biquads (which are very insensitive to the errors caused by finite accuracy in fixed-point implementations). The structure is especially good at isolating small-amplitude sinusoids when in the proximity of much larger sinusoids of unknown frequencies