Hi all. I need to plot a Fast Fourier Transform(FFT) of a sinc function

Venu Kumar Yadav Hosur (view profile)

on 18 Apr 2015
Latest activity Commented on by Image Analyst

Image Analyst (view profile)

on 18 Apr 2015
Hi everyone. I need help on Fast Fourier Transform. By using FFT plot a Sinc function & find the normalization & then also plot the inverse F.F.T of Sinc function and find out the normalization.
Thank you.

on 18 Apr 2015
So what is the problem? I assume you have searched the Matlab help and found the sinc function and the fft and ifft functions. Or do you just want other people to do all the work for you instead?!
Image Analyst

Image Analyst (view profile)

on 18 Apr 2015
I would ask your instructor for clarification on what "find the normalization" means. It's not standard terminology, or at least I'm not familiar with it. Maybe he means "normalize the curve before you plot it" or something like that. If so, does he want the y height normalized to 1, or the area under the curve?

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Answer by Youssef Khmou

Youssef Khmou (view profile)

on 18 Apr 2015

Let us consider non causal function, we can use built in function as follows :
Fs=42;Ts=1/Fs;
t=-1:Ts:40*Ts-Ts;
f=5;
y=sinc(pi*t*f);
figure;
plot(t,y);
xlabel('x');
ylabel(' magnitude');
N=512;
fy=(fft(y,N));
figure;
fr=(0:N-1)*Fs/N;
%fy=fy(1:floor(end/2));
%fr=fr(1:floor(end/2));
plot(fr,fftshift(abs(fy)));
xlabel(' frequency x^{-1}');
ylabel(' magnitude'); The width of range is approximately pi*f=15.70.
the second part requires ifft function.