Ambient noise canceller in pulmonary sound using WHT transform domain adaptive filter

In the process of signal processing of pulmonary sounds, the cancellation of ambient noise is very important. Because the ambient noise is a wide band signal in the frequency domain, it usually uses an adaptive noise canceller (ANC) structure to cancel the ambient noise. However, the usually used algorithm, normalized least mean square (nLMS) algorithm, may fail when dealing with the ambient noise due to the time-varying system because of its low convergence speed. We use a transform domain adaptive filter (TDAF) with a Walsh-Hadamard transform (WHT) to improve the convergence speed. The simulation results show that this structure would cancel the ambient noise more efficiently.