An optimal high-pass filtering technique to improve the detectability of evoked otoacoustic emissions

Evoked otoacoustic emissions (EOAEs) are currently used as the most reliable test for hearing screening. The presence of emission is commonly detected by the visual inspection of the signals and the cross-correlation function between replicate responses recorded in the same conditions. Performances of these methods are greatly 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 here. Crosscorrelation between replicates of transient evoked otoacoustic emissions (TEOAEs) was used to determine the cut-off frequency that maximises the S/N ratio. This will be shown in a series of responses characterised 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.