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Keywords: Normalized root mean square error (NMRSE) , Peak signal to noise ratio (PSNR) , PCG signal , Wavelet transform.

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In this paper, we present a method for single channel noise reduction of heart sound recordings. Multiple noise sources, such as lung sounds, muscle contraction and background noise can contaminate the heart sound collection making subsequent analysis difficult. This method uses a “decision-directed” approach to estimate the noise without the need for a separate reference signal. The wavelet de-noising method based on three thresholding functions is used for heart sound signals de-noising; soft-thresholding and hard-thresholding functions are traditional and an improved novel thresholding function with double variables parameters is novel. The critical point of the wavelet based de-nosing of signals is the choice of the wavelet and thresholds. The change of wavelet can give different results. It can overcome the shortcoming discontinuous function in hard-thresholding and also can eliminate the permanent bias in soft-thresholding. We have developed the function this denoises the PCG signal by different wavelets and results the selection of suitable wavelet that is best for a complex signal.


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