Parameterize overlapping - cpsd()

Hello, everyone.

I need to create a script where overlapping is parameterized. I did it this way:

N = length(u); % = length(y)

percentage = 0.5; %range = [0.01 - 0.99]

window = hanning(round(N/4.5));

overlap = round(length(window)*percentage);

[SuyW,fw] = cpsd(u,y,window,overlap,[],fs);

Can anyone tell me if this is correct?

Answer 1

[William Rose]

@Amanda Santos,

[edit: correcting my recommendation from overlap=floor(...) to overlap=ceil(...)]

Yes this is reasonable.

You can answer your quesiton by trying some different values for N and observing the resulting values for window length and overlap:

%N = length(u); % = length(y)
N=[500,1000,2000,4000];
percentage = 0.5; %range = [0.01 - 0.99]
for i=1:4
    window = hanning(round(N(i)/4.5));
    overlap = round(length(window)*percentage);
    fprintf('N=%d, winLen=%d, overlap=%d\n',N(i),length(window),overlap);
end

N=500, winLen=111, overlap=56
N=1000, winLen=222, overlap=111
N=2000, winLen=444, overlap=222
N=4000, winLen=889, overlap=445

The results look reasonable.

You chose a window length that is 1/4.5 times the signal length, in all cases. This choice will usually allow for 8 half-overlapped windows in the signal. It is possible that, due to rounding, the 8th and final window will not fit. For example, N=98, N=502, N=512, N=1006, N=1024, and others. Therefore I would use

window = hanning(floor(N/4.5));

overlap = ceil(length(window)*percentage);

to assure that the window goes onto the signal 8 times.

[Amanda Santos]

Thank you!

[William Rose]

You're welcome, @Amanda Santos. If my answer suffices, please accept it. Good luck with your work.