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Table 2 Heart sound denoising techniques

From: The electronic stethoscope

References Categorya Sensor type No. of sensors Method Outcome
[33] Time Electret condenser microphone 2 LMS-ANC External noises are reduced by 12.92–16.11 dB
[34] Time Electronic stethoscope 1 Single input ANC Most of breath sounds and noises are suppressed, performance robust to heart beat rate
[35] Time Microphone 1 LMS-ALE, RLS-ALE HS recovery and noise reduction are 91–93% and 89–92%, respectively, for LMS-ALE; for RLS-ALE, they are 95–97% and 90–92%
[36] Time NA NA Variable step size Griffith LMS-ALE The SNR gain is 7.85 dB
[37] Frequency Audicor system [38] 2 SS, FFT Better noise removal; improved ability to detect S3 and S4 sounds
[39] Frequency Electronic stethoscope with electret microphone 1 DWT, Hilbert transform Recommendations on optimal parameters selection are given
[40] Frequency Microphone 1 DWT, LMS-ALE, RLS-ALE RLS-ALE and DWT with SURE shrinkage give best results
[41] Frequency NM NM EMD EEMD seems to be a good solution for HS denoising
[42] Frequency NM NM EMD S1 and S2 can be extracted with high accuracy
  1. NA not available, NM not mentioned.
  2. aCategory: denoising in time/frequency domain.