Extraction of FFT from each segment for computation

Hello! I have a code doing splitting of data size of 51200 into segments of 512 and did a FFT on each segment.

How do I extract the FFT from each of the 512 segment ?

[Sindar]

Your question is unclear. What's already working and what do you need?

Answer 1

[Star Strider]

If this relates to your earlier Question, the fft results are in each column of the ’P1’ matrix.

Y = fft(X-mean(X));             % FFT
f = Fs*(0:(L/2))/L;
P2 = abs(Y/L);
P1 = P2(1:numel(f),:);          % Note: Added Column Dimension (I Did Not Catch That Omission Earlier)

so the first fft would be:

FT_1 = P1(:,1);

and so for the rest.

[Chloe Sim]

Hello! Thank you for the response! I have a question!

In my workspace, P1 have 1x25601 double value.

I am not sure what it means, because I am assuming that P1 will have 520 FFT values only.

[Star Strider]

My pleasure!

See if this answers your question:

P1 = rand(1,25601);                         % Create ‘P1’
L = 512;
X = buffer(P1, L);
Y = fft(X-mean(X))/L;
f = Fs*(0:fix((L/2)))/L;
P2 = abs(Y/L);


figure
subplot(2,1,1)
plot(f, P2(1:numel(f),1))
grid
title('P2(:,1) = First Column')
xlim([0 max(f)])
subplot(2,1,2)
plot(f, P2(1:numel(f),20))
grid
title('P2(:,20) = 20^{th} Column')
xlabel('f')
xlim([0 max(f)])

Here, ‘P2’ has 512 rows and 51 colimns. Each column is a separate fft.

This also demonstrates how to address them and how to plot them.

[Chloe Sim]

Hello! Thank you for the fast response!

Is the code above showing each FFT of each segment? :)

[Star Strider]

It is showing the fft for the segments (columns) you choose. In that example, I plotted columns 1 and 20.

To show all of them in the same axes at the same time:

figure
plot(f, P2(1:numel(f),:)
grid

Experiment to get different results.