“…On the other hand, the artificial intelligence-based methods extract many time-domain, frequency-domain, or time-frequency-domain features from each PCG segment, which are then used to train a classification model. Several machine learning or deep learning algorithms, such as k-nearest neighbor, support vector machine, hidden Markov model, decision tree, k-means clustering, logistic regression, and neural networks, have been implemented to discriminate between S1, S2, S3, and S4 heart sounds, and also to distinguish heart sounds from murmurs [ 25 , 27 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ] and to recognize abnormal heart sounds [ 44 , 45 ]. Although they achieve high classification performance, artificial intelligence-based methods are far more complex than envelogram-based algorithms in terms of computational burden and require the a priori knowledge of the heart sounds for labelling PCG segments and training a classifier.…”