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Topic: FFT on 320e3 points
Replies: 2   Last Post: Mar 6, 2013 9:38 AM

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Nasser Abbasi

Posts: 6,677
Registered: 2/7/05
Re: FFT on 320e3 points
Posted: Mar 6, 2013 8:14 AM
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On 3/6/2013 5:09 AM, Giorgio wrote:
> Hello,
> I am working on a project where I need to calculate the FFT of a Signal.
> This signal is one period of a sinusoid, sampled on 64 points.
> Every 100 periods the phase of the sinusoid change by a random angle (+- pi/2 or -+ pi) and this for 50 times.
> So, at the end of simulation (Simulink), the result is one dimensional Array of 1 X 64*100*50 = 320e3 points .
> I need to calculate the FFT, so I am trying to import the Array in Matlab.
> But, I have the suspect that Matlab does an approximation or a decimation of the orginal signal.
> By default, the FFT is fixed on 1024 points?
> So, how I can force Matlab to calculate the fft EXACTLY on 320e3 points ? Maybe this take one hour or more, but I don't care.
> Thanks in Advance.
> Giorgio.


May be try fft(X,n) ?

"Y = fft(X,n) returns the n-point DFT. fft(X) is equivalent to
fft(X, n) where n is the size of X in the first nonsingleton dimension.
If the length of X is less than n, X is padded with trailing
zeros to length n. If the length of X is greater than n, the sequence X is truncated."

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