how can i find the value for the amplitude and frequency using fft?

Question

Abba Alhaji Bala 2019-2-27

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https://ww2.mathworks.cn/matlabcentral/answers/447239-how-can-i-find-the-value-for-the-amplitude-and-frequency-using-fft

评论： Abba Alhaji Bala 2019-2-28

Hi everyone,

please i want to find the value for the maximum amplitude and the frequency. i used the abs of the fft for the amplitude but the amplitude value i am having does not tally with that from the figure (from the figure is around 2-2.2 while am having from the fft 8900). also, i used several methods from this page for the frequency value but its returning with a vector not value. The oscillations have no sampling frequency, so i used fs = 1/T.

Time = 0.2-0.3ms  %the vector values= 250000x1 double
% to find the amplitude
p=signal
pt=signal time 
t1=0.2
t2=0.3
pttt=find(pt>ti&pt<t2)
a=fft(pt(pttt))
aa=abs(a)
aa_max=max(aa)   % it will give value of 8900
% to find the frequency value
f=find(aa==aa_max)
f_exst=(f(1,1)-1)*fs/N    % but am not sure of the value it gives