(A, B, C, D). Changes in the STFT Spectrogram due to change in the window size. PCG is shown on Fig. 9A, Spectrograms shown on A), B) and C) were obtained using Meditron Analyzer software distributed by Welch-Allyn, NY. Also compare against the Fig. 2 obtained using HES method. [see Additional file 1]. A) Window size w = 1024 points (better time resolution). B) Window Size w = 2048 points. C) Window Size w = 4096 points (better frequency resolution). D) HES spectrogram (see also in greater detail in Figs. 2(A-C)).