How to plot trend lines of 2 FFT graphs which have very large data points?

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Nopparat Seemuang
Nopparat Seemuang 2014-9-15
评论： Omar Alngar 2016-6-10
Dear Guys!!
I got the problem on plotting FFT graph by Matlab. I need to compare FFT of 2 signals in the same graph.
From the attached pictured, those two signals were sampled from 600kHz, 10 sec. When I plot them on graph, it look like the filled pattern which is very hard to compared. I need to plot by 2 trend lines (unfilled like example in the middle graph).
I have tried several days to find the way to plot them like the graph in the middle of picture.
Nae = length(ae);
fs1 = 600000; % sampling rate of signal
t = [0:Nae-1]/fs1;
ff = (0:Nae/2)*fs1/Nae;
AE = fft(ae); AE(1)= [];
power = abs(AE(1:length(ff))*2/Nae).^2;
AE2 = fft(ae2); AE2(1)= [];
power2 = abs(AE2(1:length(ff))*2/Nae).^2;
h = figure(2);
plot(ff,power,'b',ff,power2,'r');
legend('Signal 1','Signal 2');
Any suggestion ???
Thank you very much

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回答（1 个）

Youssef Khmou
Youssef Khmou 2014-9-15
One temporary solution is to downsample the two power spectra, this proposition is based on time-frequency uncertainty principle, since the physical resolution will not improve unless you have more samples in time domain, so you can truncate elements :
f=20;
Power=power(1:f:end);
Power2=power2(1:f:end);
% try with different values of gap f, or use downsample(power,c) function .
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Nopparat Seemuang
Nopparat Seemuang 2014-9-22
I have just tried. The graph looks like my need. How can I modify to meet my request of two fft compared in the same graph?
Thanks

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