Bessel filtering of brain stem auditory evoked potentials.

It has been shown previously that conventional high-pass filtering of the brain stem auditory evoked potential (BAEP) results in significant wave form distortion. This distortion can be drastically reduced by using digital filters with zero-phase properties, but this approach requires the use of a digital computer. The Bessel filter is an approximation to a linear phase characteristic, and has the advantage that it may be implemented using analog circuitry. We have considered its use as an alternative-to-digital zero-phase filtering. For the low-pass case, the Bessel phase characteristic is approximately linear throughout the pass band. However, for the high-pass case there is significant phase non-linearity extending well into the pass band. Typical Bessel high-pass filters seriously distort the BAEP wave form; thus, these filters are not an acceptable alternative to the zero-phase digital approach.