[Frequency spectra and filtering of the early auditory evoked potential]

We analysed the spectral content of click-evoked fast auditory evoked potentials (FAEPs) at stimulus levels of 80 dB nHL and were able to demonstrate the influence of the different frequency bands of the FAEP spectrum on the shape of the FAEP. The different kinds of filter and their typical effects are discussed, and some examples are demonstrated. Analogue high-pass filters with a steep slope change the shape of the FAEP markedly, because of the great phase distortion (non-linearity of the phase function). Therefore only one-pole filters (6 dB/octave) with a low cut-off frequency below about 70 Hz should be used. Higher cut-off frequencies can be used with digital zero-phase or linear-phase highpass filters. However, such frequency components which are essential for amplitudes and/or latencies of the FAEP should not be attenuated strongly by the filtering. Therefore, the low cut-off point should not exceed about 200 Hz.