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. 2016 Sep 9;6:33182. doi: 10.1038/srep33182

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Copyright © 2016, The Author(s)

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/

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This flow diagram depicts the process for extraction of Mel-Frequency Cepstral Coefficients (MFCC) from the second heart sound (S2). The identified S2 is pre-processed with a pre-emphasis filter. It is divided into frames lasting 25 milliseconds and a Hamming window is applied to each frame. The following operations are then performed on each frame: (1) Fast Fourier Transform (FFT) (2) frequencies are linearly spaced into a mel frequency bank, (3) a logarithmic transformation is applied, and (4) a discrete cosine transformation is applied. These steps generate the mel-frequency cepstral coefficients that are used as feature vectors for the training and testing stages.