Short-time Fourier transform analysis of the phonocardiogram signal

In this paper, we present results of the PCG (phonocardiogram) signal analysis using the STFT (Short-Time Fourier Transform). Because of the nonstationarity of the PCG signal, it is important to maintain an analysing time window as short as possible to guaranty the stationarity hypothesis over small analysed segments. This will reduce the frequency resolution of the resulting spectrogram. However by adjusting the sliding time window, we can reach an acceptable result. The spectrogram is calculated by using first, short length sliding window to generate a temporal representation of the PCG, then longer length sliding window in order to generate a spectral representation of the PCG power. The resolution in such representations depend directly on the sliding window length. The temporal representation allows heart sounds and cardiac cycle durations to be measured. Whereas the spectrum, assuming a good frequency resolution, allows spectral characterisation of each heart sound. The results we obtained on normal PCG signal, show that the STFT analysis provides a clear comprehension of the cardiac events when the spectra are represented in the time-frequency scale basis. Such results confirm the normal aspects of the analysed PCG signal.