The human ear is insensitive to phase in the Fourier expansion of a periodic waveform:
given a periodic signal [math]A_0/2+\sum\limits_{n=0}^{+\infty}A_n\cos(nt+\phi_n)[/math],
we can replace it with [math]A_0/2+\sum\limits_{n=0}^{+\infty}A_n\cos(nt+\tilde\phi_n)[/math],
where we changed the phase angles [math]\phi_n[/math] with randomly chosen [math]\tilde\phi_n[/math]. The two waveforms are possibly very different, but sound exactly the same!
