# How to combine multiple spectrogram and create a single image in MATLAB

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Stephen john on 12 Sep 2022
Commented: Walter Roberson on 25 Sep 2022
Hello I hope you are doing well. I have the 3 vectors. I want to create a spectrogram of each vectors first save the spectrogram.
and combine the three vectors to create a single overlap spectrogram and save as image file
How can i do it in MATLAB

Walter Roberson on 12 Sep 2022
When you permit spectrogram() to display the result, then it always clears the axes it is drawing in. spectrogram() does not just display the result: the output has active controls.
Because of this, if you let spectrogram() display the output, you cannot merge the results at all easily.
What you can do is ask for outputs from spectrogram(), and use the outputs to draw the results any way that is appropriate for you.
But perhaps I am misunderstanding you. Perhaps what you want to do is something more like
combined_signal = mean([first_signal(:), second_signal(:), third_signal(:)], 2);
This assumes that they are all the same length; if not then you will need to pad the shorter ones first.
Walter Roberson on 25 Sep 2022
s_rate=200;
dt=1/s_rate;
n = 1;
nov = length(acc(:,n)); %my acc has the dimensions (262144,1)
section1 = ceil(nov/13); %window my acc data in 13 segments
window1 = hanning(section1); %apply a hanning fenster on it
noverlap1 = ceil(3*section1/4); %75% overlapping
f= [0 100]; %my frequencies go from 0 30-40 Hz so i choose to take max f intervall
[s,f,t,psd] =spectrogram(acc,section1,noverlap1,f,s_rate,'psd');

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