Effects of high-pass filtering on the detection of the auditory brainstem response

The effects of high-pass filtering on the slow components of the click-evoked auditory brainstem response (ABR) have been assessed in eight normally hearing adults. Eight high-pass Butterworth-type filters (36 dB/octave) were investigated with cut-off frequencies at 10, 20, 30, 40, 50, 60, 80 and 100 Hz (-3 dB points). The low-pass filter was kept constant at 1 kHz. A 20 dB nHL stimulus was presented to the subjects at a rate of 26/s. Two averaged ABR waveforms, each consisting of 2048 individual sweeps, were recorded for each filter setting with a post-stimulus sweep time of 19.2 ms. In the visual interpretation of the recordings the correlation between each waveform, and the amplitude of the response relative to the noise, strongly affects the decision as to whether a response is present. A mathematical analysis of these parameters, using a scanning correlation window technique, showed that a 20 Hz filter is optimum for the best detection of the ABR close to hearing threshold.