Some Aspects of EEG Frequency Analysis

The purpose of this article is to give a short mathematical introduction to the analysis of EEG signals by means of frequency-selective filters. Besides the resonant frequency, three characteristics of practical filters turn out to be of primary importance. These characteristics are: 1) the time selectivity (width of the window function), indicating the duration of the part of the signal under investigation; 2) the frequency selectivity as bandwidth of the filter; 3) the efficiency, i.e., the ratio of the standard deviation of the filter output to the mean output, in case random noise is fed into the filter.