A study on single-channel non-stationary noise suppression for cardiac sound

In recent years, the need for health care continues to grow, thereby leading to the widespread use of home-oriented health care and medical equipment. An example of the same is the use of the digital stethoscope. Our research aims to accurately monitor a user's cardiac status 24 hours a day at any location using a wearable device with an in-built digital stethoscope. A presently existing challenge is that the cardiac sound monitored with digital stethoscopes is often mixed with ambient noise or overlapped with vibrations from body movement. This study investigated a means to suppress sudden non-stationary noise from a single-channel stethoscope signal. We propose a method in which we assume the excitation signal to be a non-stationary noise component in the linear prediction analysis. Compared with the spectral subtraction method, which continually updates the noise spectrum, our method improves the spectrum distortion by 2.0 dB, and improves the degree of noise suppression by 4.6 dB.