S. Kapadia et Me. Lutman, Static input-output non-linearity as the source of non-linear effects in maximum length sequence click-evoked OAEs, BR J AUDIOL, 35(1), 2001, pp. 103-112
The application of the maximum length sequence (MLS) technique to the recor
ding of click-evoked otoacoustic emissions (CEOAEs) allows for a reduction
in test time by one to two orders of magnitude. This is because the techniq
ue permits the use of extremely high click rates, as inter-click intervals
are not constrained to be greater than the duration of the response. Howeve
r, increasing the click rate also causes a progressive reduction in amplitu
de, or 'suppression', of the CEOAE. The origin of this suppression is uncle
ar, with diverse suggestions in the literature as to its nature and mechani
sm. This paper presents a simple model of the well-known compressive non-li
nearity of the CEOAE level function, based on a static amplitude non-linear
ity within each of a number of narrowband frequency channels. The response
of the model to MLS stimulation demonstrates suppression broadly of the for
m and magnitude previously reported in experimental studies. Furthermore, t
he model exhibits the generation of additional non-linear components that h
ave been speculated on in connection with CEOAE recordings using the MLS te
chnique. It is concluded that the MLS suppression phenomenon is derived lar
gely, if not entirely, from the static non-linearity of the CEOAE level fun
ction. The approach to modelling the phenomenon as described here also bear
s promise for understanding various aspects of non-linearity in MLS -based
CEOAE recordings.