Absolute/averaged spectral power of 128 channel EEG signal

Question

I have a EEG signal with 128 channels and 500 samples as 128*500 matrix. I know we can calculate power spectral density using pmcov or pwelch in matlab for any discrete time signal. But is there any way in which I can calculate absolute or averaged spectral power for the entire signal? So that I have just one absolute power on y-axis and corresponding frequencies on x-axis which can be used to represent the entire signal?

Thanks a lot for the help!

Answer 1

You can do it as follows:

% assume x is 500-by-128 matrix
pxx = pwelch(x);

% convert to dB
pxx = 10*log10(pxx);

% take average across channels
avgPwr = mean(pxx, 2);

Note that I am assuming x to be 500-by-128, because pwelch computes columnwise power.