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

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

[Omar Alngar]

Hi do you find the solution for this it is my problem too

Answer 1

[Youssef Khmou]

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 .

[Nopparat Seemuang]

thanks so much, Youssef

I have tried to resample but the signal changes because lost some important data point resulting in lost of some frequency content. this should be avoid for my work.

[Youssef Khmou]

can you use correlation function between the two signals? (xcorr(power,power2)) ?

[Nopparat Seemuang]

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