(A,B,C,D,E). Comparison of HES and STFT frequency resolution on the spectrogram, simulated S2 split function [see Additional file 3]. A) Phonocardiogram: two realistic S2 narrow split test. B) HES Spectrogram (two separate energy contours are clearly seen). C) STFT w = 256 Spectrogram (separate counters united together, split is lost). D) HES Integral Power Plot showing excellent split resolution accuracy at mid point DTS1 = 14.6 % of the peak, DTS2 = 2.9% of the peak. E) STFT Spectrogram w = 256 Power Plot (split is completely lost) accuracy at mid point DTS1 = 78.5% of the peak, DTS2 = 66% of the peak.