FFT of discrete time domain data
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Hello,
I would appreciate if anyone could help me to figure out the following problem.
I have 512 samples, the samples are taken within 1 microseconds of time interval. I would like to see the signal from 6 microseconds to 5.17e-4 seconds in frequency domain.
I have already tried the following codes in MATLAB, but it only gives me the time-domain representation of signal.
T = 5.17e-4;
N=512;
t=linspace(6e-6,T,N);
X=fft(data);
X = X/N;
dt = t(2)-t(1);
fs=1/dt;
fn=fs/2;
f=linspace(0,fn,length(t)/2);
X1=X(1:length(t)/2);
X1=abs(X1);
plot(f,X1);
I look forward for your reply. Thanks.
2 Comments
Rick Rosson
on 4 Jul 2011
1. Can you tell me the size of |data| and what type of signal it represents?
2. Why are you calling the |fft| function twice? Why not just once?
Answers (2)
Rick Rosson
on 18 Aug 2011
In the following code, I am assuming that data is predefined as a column vector of size N x 1. If it is a row vector of size 1 x N, then either transpose data or change the first line of the code to take the number of columns instead of the number of rows.
%%Number of samples:
N = size(data,1); % assumes data is an N x 1 column vector
%%Compute the time domain:
Fs = 1e6; % samples per second
dt = 1/Fs; % seconds
t = dt*(0:N-1)';
T = N*dt;
%%two-sided spectrum, centered on DC
X = fftshift(fft(data))/N;
%%Compute the frequency domain:
dF = Fs/N;
f = (-Fs/2:dF:Fs/2-dF)';
%%Plot the time domain signal:
figure;
plot(t,data);
%%Plot the magnitude response:
figure;
plot(f,abs(X));
HTH.
Best,
Rick
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