Need help for averaging FFT of segment

Dear All,

I would like to ask you in such problem that i am facing now, since i am still beginner in the Matlab programming. Currently, I have signal with length of 1000 sample and I would like to devide it to be 10 segments so each of them will have 100 sample. For each segment I would like to implement FFT and windowed function. And finally, I want to calculate the average FFT for these 10 segments.

I have FFT program but it i is used for calculating for FFT of 1000 samples. I have tried to use "for" function but it seems useless for me. Would you help me by correcting my sample signal below to fulfill my objective? Thank you in advance

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Fs=100;
Ts=1/Fs;
t=0:Ts:1000-Ts;
n=length(t);
y=2*sin(2*pi*0.5*t)+5*sin(2*pi*0.2*t)+10*sin(2*pi*0.1*t)+20*sin(2*pi*0.05*t);
figure(1)
plot(t,y)

windowHann=window(@hann,n).';
hannWindowFigure=figure;
plot(windowHann);

windowedSignal=windowHann.*y;
windowedSignalPlot=figure;
plot(t,windowedSignal)

[Yk,k]=positiveFFT(windowedSignal,Fs);
Yk=Yk*2;
fftWindowedSignalLinear=figure;
stem(k,2*abs(Yk));

xlabel('Spatial frequency (m-1)')
ylabel('|Y(k)|')

------------------------------------------------------------

Positive FFT is function with
function[YfreqD,freqRng]=positiveFFT(y,Fs)
N=length;
k=0:N-1;
T=N/Fs;
freqRng=k/T;
YfreqD=fft/N;
cutOff=ceil(N/2);
YfreqD=YfreqD(1:cutOff);
freqRng=freqRng(1:cutOff);

I do not know what your "positiveFFT" is and a few other variables. At any rate, here is a simple code that calculates the average FFT. I do not have matlab with me, so you might have to tweak it a little bit:

Hello Joannes,

Many thanks for your reply. I have tried to input your code such as below :
-----------------------------------

Fs=100;
Ts=1/Fs;
t=0:Ts:1000-Ts;
n=length(t);
y=2*sin(2*pi*0.5*t)+5*sin(2*pi*0.2*t)+10*sin(2*pi*0.1*t)+20*sin(2*pi*0.05*t);
figure(1)
plot(t,y)

windowHann=window(@hann,n).';
hannWindowFigure=figure;
plot(windowHann);

Y_average=zeros(1,n);
w=sum(windowHann);
for m=0:9
Y=fft(y(1+m*n:n+m*n).*windowHann)*(2/w);
Y_average=Y_average+Y.*conj(Y);
end
fftWindowedSignalLinear=figure;
stem(abs(Y_average));
------------------------------------------------

However there is an eror notified :

"??? Index exceeds matrix dimensions.

Error in ==> FFT10segment at 17
Y=fft(y(1+m*n:n+m*n).*windowHann)*(2/w);

I also had correct the meaning of Postive FFT. And actually i am intended to windowing my signal for each segment before i am performed FFT. Any further help will be highly appreciated . Thank you so much.

mmm... if you read the code you will notice that n should be divided by the number of averages you want to take, in this case n=n/10;

Dear Dr Joannes,
I am sorry, I tried to configure the new logarithms ,,but it seems not working. If you dont mind, May you see it what was the mistake that I have done..
--------------
fo=5;
Fs=100;
Ts=1/Fs;
t=0:Ts:0.9-Ts;
N=length(t);
y=2*sin(2*pi*fo*t);

Nseg= 10; %Number of segments
n=floor(N/Nseg); %Nu. of samples per segment

Y_average=zeros(1,n);
for I=1:Nseg %number of segment
w=hann;
y1=y(1:n,I); %signal from segment 1 until segment 10
windowedSignal=(w(1:n,I).*y1; %windowoded signal for each segment

Y=fft(windowedSignal,n); %fft for each signal segment
end
%averages FFT
Y_average=Y_average+Y.*conj(Y);
stem(abs(Y_average));
------------------------

thnak you very much

What a mess... here is the code. Again I did not test it... Please look up the fftshift function to understand what it does...

Dear Dr Joannes.

Yes I have modify and it is fit with my calculation right now. You are so much helpful.

Thank you so much for your kindness.

Best regards,

Agus