Periodic Disturbance Cancellation Using a Generalized Phase-Locked Loop

An effective technique for extracting an audio input from a composite signal that contains a nonstationary noise-corrupted periodic disturbance is presented. The proposed technique cancels the periodic disturbance using a synthesized signal whose parameters are adjusted adaptively. A combination of a generalized phase-locked loop (PLL) and an adaptive least mean square (LMS) method is used. The PLL creates a pair of basis signals that are phase-locked with the fundamental harmonic of the periodic disturbance. Harmonics generated from these basis signals are then used in the LMS method to minimize the average power of the residual nonperiodic signal. The virtue of this approach is that it does not depend on an explicit accurate estimate of the fundamental frequency of the disturbance. Furthermore, relatively large changes in the fundamental frequency can be tracked so long as they remain within the acquisition range of the PLL. Simulations and experimental results are presented that demonstrate the effectiveness of the proposed technique.