# Plotting spectrogram for EEG data

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Sparsha Kumari on 5 Feb 2020
Commented: Walter Roberson on 7 Feb 2021
Greetings!
I am done with the filtering and plotting the power spectrum for the EEG data. Now I want to plot the spectrogram for this data. I have tried using the 'spectrogram' and 'stft' function and played with the various input options but I do not get the plot the way I want it to be. Could someone please show me some light in this regard.
Thanks!
P.S. : I need to get it as shown in figure 1 (Reference: William E. DeCoteau et. al. www.pnas.orgcgidoi10.1073pnas.0700818104). Instead I get it as shown in the figure 2.
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Sparsha Kumari on 5 Feb 2020
Thanks a lot for your reply! I get it as shown in figure 2. I have used the 'stft' function as follows and got the plot,
stft(data, fs);
Sudon Biswas on 6 Feb 2021
Could you plz provide me spectrogram and magnitude squared coherence (MSC) Matlab code for ECG signal? The code must be for single signal example: 1. For raw signal 2. Noisy Signal 3. For noise free signal

Daniel M on 24 Apr 2020
You should plot the absolute value of your output from spectrogram or stft. Maybe even the log, or 10*log10 too (but I don't recall exactly, you'll have to look up the documentation). Basically, when you call those functions with outputs, try and make the plot match the one you get when you call the functions without outputs.
Your spectral and temporal resolution are very different from the first figure. That paper is doing a time-frequency analysis over ~ 4 seconds and 25 Hz. You are looking at ~150 ms and 500 Hz. You can look at this tutorial (with video) on how time window and frequency resolution trade-off with each other.
Sudon Biswas on 6 Feb 2021
@Walter Roberson
Walter Roberson on 7 Feb 2021
Coherence is only defined between two signals, not one signal by itself. https://en.wikipedia.org/wiki/Coherence_(signal_processing)