Filtering characteristics of ambulatory EEG recording systems

An analysis of the filtering in ambulatory EEG systems is performed. The typical ambulatory EEG system has 3 cascaded time constants each of which distorts the signal. Using a settling time criterion the analysis suggests settings or specifications for the 3 time constants in order to be equivalent to a single overall time constant. The signal distortions due to various settings are illustrated for typical EEG wave forms. It is shown that the distortion can be particularly severe when overload occurs in the ambulatory recording system, a condition that is prevalent due to high amplitude signals such as movement artifact and eyeblink.