Interesting problem

I am a newcomer in DSP.
I am using MATLAB for that.My data is in form of a N*1 matrix.
Why there is phase associated with it though its all real data(+ve integers).
If i have some other data in N*1 matrix.How can i get effective crosscorrelation.

My approach is:-
--FFT 
--filter using simple filter to remove low frquency component
--iFFt
--obtain cross and auto correlation.

Thanks in advance

"abhinav" <akashya@gmail.com> wrote in message 
news:729e705.0410061242.4c4d7d01@posting.google.com...
>I am a newcomer in DSP.
> I am using MATLAB for that.My data is in form of a N*1 matrix.
> Why there is phase associated with it though its all real data(+ve 
> integers).
> If i have some other data in N*1 matrix.How can i get effective 
> crosscorrelation.
>
> My approach is:-
> --FFT
> --filter using simple filter to remove low frquency component
> --iFFt
> --obtain cross and auto correlation.

To your first question, imagine that you have a time sequence of N samples 
to fill your Nx1 matrix / vector.
Now, assume that the first N/2 samples consist of 10 samples per cycle of 
sinkt and the last N/2 samples consist of 30 samples per cycle of sin(k/3)t.

The first N/2 samples are at one frequency that is delayed perhaps not at 
all.  The seond N/2 samples are at another frequency that is delayed by N/2 
samples.  Delay and phase are related as: phase is the integral of delay - 
so constant delay with frequency results in linear phase.  Thus, a simple 
delay introduces phase.

If you compute a Fourier Transform of temporal data, you will get amplitude 
and phase at each frequency that's output.  The amplitude and phase are 
averaged over the temporal epoch of the input data - one way to look at it.

Fred