FREQUENCY DOMAIN WHITENING OF DISCRETE TIME SIGNAL
This function generates flat Fourier spectrum for a given signal (which is originally not white) either for the full range of 0 Hz to the Nyquist frequency or for a user defined frequency band. This operation tends to sharpen signal, as well as the noise. The whitening process is often used for ambient vibration data before stacking waveforms for cross-correlation. The process is simple as Fourier transforming the signal after applying Hann window, then normalizing its magnitude, and then inverse Fourier transforming it.
xnew = whitening(x, Fs, freq, ) for the full range of 0 Hz to the Nyquist frequency
xnew = whitening(x, Fs, freq, [0.1, 20]) for 0.1 Hz to 20 Hz as an example
x = input signal (x must be a row vector)
Fs = sampling rate (e.g., 200)
freq = frequency limit for whitening in Hz (e.g., freq, [ ] or freq, [0.1, 20])
xnew = spectrally whitened signal for the full range of 0 Hz to the
Nyquist frequency or within a user defined frequency band
Example: See demo.m file
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