Plotting a Spectrogram with data from a csv file

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Win 2013-12-4

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评论： Wayne King 2013-12-4

Hi I have some data in a csv file. The actual data has 1048576 lines and is too big to upload so I'm attaching a chunk of it which has only 10462 lines of data (trial3.csv). I would like to plot a Spectrogram using these values.

I am using the following lines to plot the data.

 Array=csvread('trial3.csv');
col1 = Array(:, 1);
col2 = Array(:, 2);
plot(col1, col2)
%[S,F,T]=spectrogram(Array,32,16,32,100)

Can someone tell me how to make a spectrogram out of it please?

Thanks

Winee

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Wayne King 2013-12-4

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编辑：Wayne King 2013-12-4

在 MATLAB Online 中打开

Array = csvread('trial3.csv');
dt = mean(diff(Array(:,1)));% sampling period
Fs = 1/dt;
[S,F,T,P] = spectrogram(Array(:,2),300,280,200,Fs);
surf(T,F,10*log10(abs(P)),'EdgeColor','none');   
axis xy; axis tight; colormap(jet); view(0,90);
xlabel('Time (s)');
ylabel('Frequency (Hz)');

You did not answer the question about what is the lowest frequency you want to resolve. That basically defines your window length. I've just used 300 here which gets you down to about 1700 Hz.

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Win 2013-12-4

How would I know the number of periods the window is covering?

Wayne King 2013-12-4

Just as I told you, you multiply the length of the window in samples by the sampling period. That gives you the length of the window in time.

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Wayne King 2013-12-4

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I don't see the attachment.

You have to obtain the spectrogram on a 1-D signal, not a matrix. So is col2 your data?

What is the sampling interval for this data -- time between measurements.

I doubt that 32 points is enough to get a good spectrogram, I would recommend making your window larger than that, but without more details about your data, it's hard to make a more concrete recommendation.