FFT single-sided amplitude spectrum plot spike at 1Hz of accelerometer data

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DuckDuck 2012-4-27

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/36777-fft-single-sided-amplitude-spectrum-plot-spike-at-1hz-of-accelerometer-data

i m trying to plot the alpitude spectrum of Z-axis accelerometer with a sample frequency of ~50Hz and signal length 18429.

Fs=46.9350530441355
% t is the time vector in millisecond from 0 to 392648.965000002
L=length(y) % y is accelerometer data 18429 records
subplot(2,1,1)
plot(t,y)
title('Signal')
xlabel('time (milliseconds)')
NFFT = 2^nextpow2(L); % Next power of 2 from length of y
Y = fft(y,NFFT)/L;
f = Fs/2*linspace(0,1,NFFT/2+1);
subplot(2,1,2
% Plot single-sided amplitude spectrum.
plot(2*abs(Y(1:NFFT/2+1))) 
title('Single-Sided Amplitude Spectrum of y(t)')
xlabel('Frequency (Hz)')
ylabel('|Y(f)|')

What i get on second plot it starts with x(1), y(18.46) and than fading. the data are from accelerometer atached to car windsheald.

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DuckDuck 2012-5-3

thank you for your help. now i get this picture for the first window of fft data: http://img137.imageshack.us/img137/8308/firstwindowfftmagnitude.jpg

how can i make in matlab a spectrogram like this one http://img37.imageshack.us/img37/8367/spectrogram.jpg

now that i have the fft transformed data?

Dr. Seis 2012-5-3

I would create a new question... others who are more familiar with running the Matlab function "spectrogram" and overlaying plots will be able to help you. You do not need to transfer your time data into the frequency domain before you use "spectrogram" - you will input your time data directly.

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