Table 2 Heart sound denoising techniques
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 7.85Â 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 |