I would do a fast fourier transform for each channel (fft in matlab), so you have the frequential componentes of each channel. Then just use a function such as mesh, surf or pcolor. As these functions represent 3D surfaces, I would define X as channel, Y as frequency and Z as the value given by the FFT.
So in general lines the code will be something like this:
nFFT = 2048; % I asked for 2048 frequency points because why not.
nChannels = 64;
data_freq =fft( multi-channel-EEG-data.',nFFT);
% FFT is applied to columns, that is why it is neccesary to transpose them.
x = 1:nChannels;
y = 1:nFFT;
[X,Y]=meshgrid(x,y);
figure
mesh(X,Y,data_freq);
shading interp;
I did not try the code, so there are probably several mistakes, but if you follow this lines, it should work :). You might need to apply another .' to data_freq to represent it. Good luck!
