R. Muhler et al., REDUCTION OF RESIDUAL NOISE IN SUPRATHRESHOLD HUMAN AUDITORY BRAIN-STEM RESPONSES, Laryngo-, Rhino-, Otologie, 77(7), 1998, pp. 382-387
Background: The level of residual noise in auditory brainstem response
s (ABR) depends not only on the number of averages but also on the amp
litude of background noise and on the frequency of artifacts. This pap
er describes the influence of digital filtering and of different metho
ds of artifact suppression on the residual noise of ABRs. Method: Ampl
itude of background noise was estimated for 1033 ABRs recorded under s
uprathreshold stimulation (70 and 90 dB nHL) in 251 subjects. In 45 AB
R recordings in 15 subjects, all 4000 individual sweeps were stored fo
r off-line simulation. The power spectrum of background noise was inve
stigated using an FFT analyzer. Results: A great variability of mean n
oise amplitude was found both between subjects and in the recordings f
or each subject. Depending on the slope of the analogue 100-Hz high-pa
ss filter, mean RMS values of background noise of 4.2 mu V (6 dB/Oct.)
and 2.5 mu V (12 dB/Oct.), respectively, were found. Digital high pas
s filtering before averaging was found to increase the signal-to-noise
ratio (SNR) considerably. Conclusions: Results indicate that (i) effe
ctive suppression of low-frequency noise components can only be achiev
ed by zero phase digital filtering and (ii) if clipping of noise ampli
tude to 25 mu V is used, optimized artifact rejection as weighted aver
aging or adopted artifact rejection levels have only small effect on t
he SNR.