Reducing Periodic Noise.
One of the negative aspects of the
exponential impact window is that periodic noise components are
smeared by the window over a frequency range centered around
the frequency of the periodic noise. In an initial effort in the 1970s,
the DC component and frequency components that were periodic
in the window were filtered by taking the FFT of both input and
response channels and setting the Fourier coefficient of the noise
components to the mean values of the adjacent Fourier coefficients.
The data were then transformed back into the time domain. The
force/exponential window could then be applied to the force and
response signals.