The auditory brain stem response recorded with 60 Hz notch filters.
Line-frequency (60 Hz in the USA) interference is a common source of contamination during recording of the auditory brain stem response (ABR). Notch filters are undeniably effective in eliminating this artifact, but concerns have been expressed as to their effect on the ABR itself. Theoretical considerations suggest that the degree of distortion should be minimal if the filter is sufficiently sharp and the stimulus rate has no multiples very close to 60 Hz. Responses simultaneously recorded through three notch filters of varying sharpness confirmed this: Latency was virtually unaffected with any filter or stimulus rate, and distortion was minimal when a sharply tuned filter was used in conjunction with a stimulus rate of 23.3 Hz, whose nearest harmonic to 60 is 69.9 Hz.