[Signal processing and quality of displaying waveform at digital EEG machine]

With great advances in computer technology, the digital EEG machine was developed and has become widely used. In this paper, signal processing and quality of display of waveform at digital EEG machine were discussed to confirm its advantages and drawbacks. Signal processing on a digital EEG machine is summarized in 3 parts as follows: i) A/D conversion(sampling) of EEG signals in the head box, ii) Digital signal processing to obtain mathematically reconstructed EEG on the computer, iii) Displaying EEG on a monitor. For sampling, it was recommended that sampling rate was 200 or 256 Hz, and resolution in 12 bits or preferably 16 bits per sample. A high amplitude artifact caused EEG flattening called DC build up saturation. Montage reformatting had a clinical advantage. However, re-filtering using 15 Hz high cut filter influenced the EEG interpretation. The maximal resolution of digital EEG machine with a 17-inch CRT display using 1600 x 1200 dots was about 22 Hz. The performance of paper used for conventional EEG surpassed the performance of CRT display using digital EEG machine. It seemed that understanding the characteristics of digital EEG machine and realization of data processing were important for utilizing its functions effectively.