An optimal filtering technique to reduce the influence of low-frequency noise on click-evoked otoacoustic emissions

There is a need for methods capable of increasing the detectability of transient-evoked otoacoustic emissions (TEOAE). Detection of an emission is based commonly on either visual inspection and cross-correlation between replicate recordings or cross-spectral analysis. Performance of these methods is obviously influenced by the residual noise level. Residual noise is often of low frequency and can be reduced by digital off-line filtering. For this purpose, an optimal high-pass filtering technique is proposed. Cross-correlation between replicates of TEOAEs was used to determine the cut-off frequency that maximizes the signal-to-noise (S/N) ratio. This is shown in a series of responses characterized by various S/N ratios. Data have been scored both visually and with quantitative methods before and after the use of high-pass filtering. The capability to detect the signal was increased with only a marginal decrease in the total power of the emissions.