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Any FFT expert around?
From: |
oxy |
Subject: |
Any FFT expert around? |
Date: |
Wed, 12 Feb 2014 14:22:05 +0100 |
hey guys,
the (simple) code bellow is how i ve learned to do FFT according to
several docs online. However i observe a dependency of the signal
frequency in the spectrum on the constant FsFactor. In other words,
the signal frequency depends on the sampling rate. I should'nt be,
right? So what is wrong here?
#---------- start code ------------
clear all
nu=10; % signal frequency
at=5; % acquisition time
T1=2 % signal decay constant in time domain
FsFactor=8; % the ratio (sampling rate)/(signal
frequency), or Fs/nu
clf
Fs = FsFactor*nu; % Sampling rate
t = ((0:(at*Fs-1))/Fs)'; % Time vector
freq=linspace(-1,1,Fs*at)' * Fs/2; % frequency vector
tdsig=exp(-i*2*pi*nu*t).*exp(-t./(T1)); % time domain signal
freqsig=fft(tdsig); % freq. domain signal
subplot(1,2,1)
plot(t,tdsig)
axis([ 0 0.4]) % zooming time domain to see that period=1/nu
subplot(1,2,2)
plot(freq, freqsig)
#---------- end code ------------
Do it yourself. Just rerun the code trying different values of
FsFactor (eg: 2, 4, 8).
Thx a lot for any hint!!!
oxy
ps: cross post
http://www.mathworks.com/matlabcentral/answers/115700-fft-why-signal-frequency-depends-on-sampling-rate
- Any FFT expert around?,
oxy <=
- Re: Any FFT expert around?, Brian Kaczynski, 2014/02/12
- Re: Any FFT expert around?, oxy, 2014/02/12
- Re: Any FFT expert around?, Brian Kaczynski, 2014/02/12
- Re: Any FFT expert around?, oxy, 2014/02/19
- Re: Any FFT expert around?, oxy, 2014/02/19
- Re: Any FFT expert around?, Brian Kaczynski, 2014/02/19
- Re: Any FFT expert around?, oxy, 2014/02/20