Fig. 2

The performance of ALFP. a Is a normal heart sound, c is the filtered normal sound by ALFP, e is a heart sound with S3 and systolic murmurs, g is the murmur-eliminated sound by ALPF. b, d, f and h Are the FFT of a, c, e and g, respectively. In b, d, f and h, the yellow curves are the FFT sequences, and the blue curves are the envelopes of them. In b, the points marked by purple diamonds are two examples of spikes. In b and f, the points marked by red squares and green squares are the primary peak points and the last valley points with FFT coefficient smaller than 0.2, respectively