Effects of high-pass filter frequency and slope on BAEP amplitude, latency and wave form

The effects of increases in analogue high-pass filter frequency and slope on the BAEP were investigated in a group of 20 subjects. Frequency effects were additionally compared to the wide-band recorded signal and slope effects to a zero-phase shift filter, all filters being digitally simulated. Absolute amplitude, latency and interpeak latency were significantly reduced by both progressive filter frequency and steepness. Additionally, different effects on the ascending and descending limbs of waves I, III and V were observed which explain wave form distortions. The results suggest that filtering should be limited to, at most, 6 dB/oct and 100 Hz frequency.