njit-etd2003-081 - New Jersey Institute of Technology

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It should be noted that if the window were a simple rectangular function, the
sharp one to zero changes are the cause of the side lobes in the FFT output sinc function
(sin(x)/x). To minimize the spectral leakage caused by those sidelobes, one has to
reduce the sidelobe amplitudes by using window functions other than the rectangular
window. The purpose of the split cosine bell taper window is to reduce any additional
spectral components that result from the shape of the window. Multiplying the time
signal by the window function does the windowing. The split cosine bell taper for a
6,000-point long signal is shown in Figure 3.9.
Figure 3.9 Plot of the split cosine bell taper used as a window for FFT calculation.
Past research in power spectral analysis of heart rate variability correlates three
distinct frequency regions peaks with certain physiological parameters [14] as illustrated
by a more classical power spectrum of the IIBI signal in Figure 3.10. The very low
frequency band (0.003-0.04 Hz) is associated with vasomotor control and temperature
control. The low frequency band (0.04-0.15 Hz) is associated with baroreceptormediated
blood pressure control. The high frequency band (0.15-0.5 Hz) has been linked
with respiration.