Restoration of Lung Sound Signals Using a Hybrid Wavelet-Based Approach

• Published in: IEEE sensors journal 2022-10, Vol.22 (20), p.19700-19712
• Main Authors: Lee, Chang Sheng, Li, Minghui, Lou, Yaolong, Dahiya, Ravinder
• Format: Article
• Language: English
• Subjects: Band-pass filters; Basis functions; Denoising; Electromagnetic wave filters; Empirical analysis; Finite impulse response filters; Lung; lung sound signal; Lungs; Noise levels; Noise measurement; Noise reduction; Parameters; Root-mean-square errors; Sensors; signal estimation; Signal to noise ratio; signal-to-noise ratio (SNR); Simulation; Sound; Sound filters; Wavelet analysis; wavelets; Wiener filter; Wiener filtering; Wiener filters
• ISSN: 1530-437X; 1558-1748
• DOI: 10.1109/JSEN.2022.3203391

A unique and ideal integration of wavelet-based total variation (WATV) and empirical Wiener denoising method is proposed in this article to significantly enhance the signal-to-noise ratio (SNR) while preserving the characteristics of a lung sound signal. While individual wavelet-based denoising filters based on a single basis function have been employed in the past, the outcome has been unsatisfactory because only significant (signal) wavelet coefficients are considered for denoising analysis. The new wavelet-based empirical Wiener (WATV-Wiener) hybrid technique, proposed here, takes into account both significant and insignificant (noise) wavelet coefficients of the noisy signal. An intensive analysis of selecting and fine-tuning the WATV-Wiener filter parameters is presented here through the simulation studies. The WATV-Wiener filter applied here onto different 1-D lung sound signals of different noise levels has led to an optimal root mean square error (RMSE) compared with seven other state-of-the-art filters reported in the literature. The optimal parameters achieved through our simulation studies led to a 3-20-dB improvement in SNR, and the average SNR was improved by 4-30 dB in our experiment. We also observed that the WATV-Wiener filter is less sensitive to the variation of SNR values of the input signal. Furthermore, the WATV-Wiener filter obtains similar SNR performance between continuous piecewise signal (wheeze) and noncontinuous piecewise signal (crackle) in both simulation and experimental studies.