The first problem is that many extra ‘peaks’ are picked up. This situation is shown in Fig.3. In order to eliminate the extra peaks, the intervals between each adjacent peaks
are calculated. The low-level time limit and high-level time limit, which are used for deleting extra peaks and finding lost sounds respectively, are computed for each recording based on the mean value and standard deviation of these intervals. When an interval between two adjacent peaks is less than the low-level time limit,there must be one extra peak which should be rejected.The following criteria are used to decide which one should be dropped: (1) when two peaks appear within 50ms, which is the largest splitted normal sound interval[61, and the energy of the first peak is not too small compared to that of the second one, we picked up the first one. Otherwise, the second one is chosen. Here we assumed that the two peaks that meet the above conditions are actually two parts of a splitted heart sound.Otherwise, the first peak may belong to some other sound class or can be classified as noise. (2) when the interval between two adjacent peaks exceeds 50 ms, their energies are compared. If the energy of the first peak is larger than that of the second one and the last interval meets certain consistency of every second interval, we pick up the first one, otherwise the second one is picked UP.