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From: "Steve Amphlett" <Firstname.Lastname@Where-I-Work.com>
Newsgroups: comp.soft-sys.matlab
Subject: Re: Understanding phase in the FFT
Date: Thu, 30 Jul 2009 04:50:04 +0000 (UTC)
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dbd <dbd@ieee.org> wrote in message <8ea06202-cfd1-44cf-8656-c6c03daa210d@q40g2000prh.googlegroups.com>...
> On Jul 29, 2:35 pm, "aaaa Vadimov" <a...@hotmail.com> wrote:
> > Hi,
> >
> > Here the simple code of three series, which differ only by phase. I don't understand why I am not getting phases,which I expect to. Shouldn't I get 0 (or 360), 90 and 45 ? Thanks a lot!
> >
> > fs = 10;
> > t = 0:1/fs:50-1/fs;
> >
> > x1 = sin(2*pi*t);
> > x2 = sin(2*pi*t+pi/2);
> > x3 = sin(2*pi*t+pi/4);
> > ...
> 
> Why do you expect a sine wave to give a phase of 0 with an fft()? The
> basis vectors are cos()+i*sin().

Phase is relative.  The phase between two signals is obtained from the cross spectrum.  The phase of a single signal isn't that meaningful or useful.