about the fft plot of a discreate signal

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kavya saxena 2013-5-3

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hi all, while i m doing fft of my data received from ansys program then the frequency is highest at zero and then next peak gives correct frequency. is it possible. why it happens. what does it means.my coading is y=output(:,2); f=1e6; fs=20*f; ydft=fft(y); ydft=ydft(1:floor(length(ydft)/2)+1); freq=0:fs/length(y):fs/2; plot(freq,abs(ydft)); plot will starts from zero with peak value and second peak gives 1e6 hz. help me to understand the meaning of zero frquency.

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Answer 1

Carlos 2013-5-3

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Hi, the zero frecuency is the continous component of your signal (which is the mean value of your signal). For instance if you are working with a signal with a mathematical expression

y=cos(6*t)+2

Then 2 is the continous component of the signal.

If you calculate the fft of y-mean(y), instead of calculating the fft of your signal the continous component should disappear.