SPECTRAL WHITENING

This function applies whitening to a given signal within user defined frequency band.

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.

Syntax:
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

Input:
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])

Output:
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