# how to convert the seismic wave data in Excel to fourier spectra

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Changhyun Kim 2022년 8월 11일
댓글: William Rose 2022년 8월 15일
I want to convert the seismic wave data in the attached Excel file to the frequency [Hz] on the horizontal axis and the magnitude on the vertical axis by performing FFT in MATLAB. I'm sorry, but I'd appreciate your help.

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### 답변(1개)

William Rose 2022년 8월 11일
편집: William Rose 2022년 8월 15일
N=length(data);
t=data(:,1); %vector of times (s)
x=data(:,2); %vector of x-values
dt=(t(end)-t(1))/(N-1); %sampling interval (s)
f=(0:N-1)/(N*dt); %vector of frequencies (Hz)
X=fft(x); %compute FFT(x)
%% Plot results
plot(f,abs(X))
xlabel('Frequency(Hz)'); ylabel('|X(f)|');
grid on Try the above. As you can see, the FFT is symmetric about the Nyquist frequency, which is always half the sampling frequency . (Actually, the FFT of a real signal is conjugate symmetric about the Nyquist frequency, but we will ignore the phase for now.) Therefore it is common to plot only up to the Nyquist frequency.
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William Rose 2022년 8월 15일
I deleted the file GYEONGJU(MKL).xlsx from my comment, as you requested.

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