Projects:2014S1-19 Analysis Of Heart Sound Signals using the Wavelet Transform

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Project Information

Project Introduction

Auscultation with a stethoscope is one of the most important tools in diagnosing the heart diseases. However diagnosing the heart disease through auscultation is subjective.It depends largely on hearing ability and skills of physicians. Our project research is to develop a standard heart sounds diagnosing tools which is able to recognize the characteristic of the heart sounds and able to classify the heart sounds automatically.

Modelling of heart sound

Heart sounds provides information about people's physical conditions. The first heart sounds (S1) occurs at the beginning of ventricular contraction during the closure of the mitral and tricuspid valves,which indicates the beginning of ventricular systole. The second heart sound (S2)marks the end of ventricular systole and the begining of ventricular relaxation, following the closure of the aortic and the pulmonary valves. The identification of systole and diastoel is important in determing other heart sound and murmurs. Heart murmurs also may be present in the phonocardiogram (PCG), are generally assocated with abnormal function of the cardiac valve, except for the innocent murmurs which may occur during systole in young people with normal hearts. The murmur can be classified as systolic murmurs and diastolic murmurs according to their production phase.

Different methods


As the PCG signals are complex signals that are very difficult to analyze visually, they can be transformed to frequency domain to analyze. However heart sound signals are non-stationary signals whcih means the time components are important as well, therefore FFT cannot indicates some sudden situations. Fft comparison.jpeg The FFT (Fast Fourier Transform) can provide a basic understanding of the frequency contents of the heart sounds. However, FFT analysis remains of limited values if the stationary assumption of the signal is violated. Since heart sounds exhibit marked changes with time and frequency, they are therefore classified as non - stationary signals. To understand the exact feature of such signals, it is thus important, to study their time – frequency characteristics.


The STFT is obtained from the usual FT by multiplying the time signal x(t) by an appropriate sliding time window w(t). It provides some information about time and frequencies that a signal event occurs. However, one can only obtain this information with limited precision, which is determined by the size of the window,also, it has strict limitations on time-frequency resolution.


The wavelet transform is also used to analyze the heart sound in time and frequency domains. It uses narrow windows when observing the high frequency and automatically uses wide window when observing the low frequency. This particular property of wavelet generates good time resolution at high frequency and good frequency resolution at low frequency. Cwt.jpeg


Different features can be found through the spectrogram. Example.jpg


Group members

XiaoBo Xue

Jie Ren

Yue Liang


Brian NG

Jagan Mazumdar