How to plot microvolts values in matlab?

2016 2 9
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更新时间：2016 2 11
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Hi. I have eeg data that are in microvolts from emotiv.Fs=128 aquisition time=1min. When i plot the signal with the time vector t=0:1/Fs:60 i can see it.But when i do fft and plot it with the frequency vector freq=(1:length(signal))*fs/length(signal) the plot is so small i have to zoom in to see it.How can i set the axis to microvolts to prevent this?

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Star Strider
Star Strider 2016-2-9

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You may have a significant d-c offset. Subtract the mean of the signal from the signal before you do the fft. This will have no effect on the frequency content of your signal.

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vaggelis papasot
vaggelis papasot 2016-2-11
Thank you very much for your answer!I had a suspicion about the dc offset,but reading the emotiv epoc specifications pdf https://emotiv.com/product-specs/Emotiv%2520EPOC%2520Specifications%25202014.pdf it says it has 50-60hz notch filter and thought it was to cut line noise.Now plotting a channel AF3 in time domain before cutting of the dc has its first value at 500uV,then cutting dc by AF3=AF3-mean(channel1) centers the signal at 0.Also plotting the signal with dc off at frequency domain gives a clear view of the frequency plot and is more visible that the signal is filtered between 0.2-45Hz.I hope that if anyone else is having the same problem with eeg data from emotiv or emokit will benefit from this question.Thanks again for your answer!
Star Strider
Star Strider 2016-2-11
As always, my pleasure!
My own experience with biomedical signal processing led me to hypothesise the d-c offset problem. Thank you for your detailed analysis.

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