Operating Instructions
62
TEOAE
The calibration phase automatically measures the peak pressure obtained from a sequence of clicks and
calculates the voltage required to obtain the target peak pressure. If the desired peak pressure cannot
be obtained, the unit will use the maximum voltage.
The test phase consists of measuring the response obtained from repeated sequences of clicks applied
to the receivers. The click sequence is 3-1-1-1 repeated twice. Signal and noise floor estimates are
obtained by adding/subtracting the two response sequences respectively. The energy of the signal and
noise floor estimates in various frequency bands is obtained in real time and displayed once per second.
The average peak pressure of the stimulus is calculated after completion of the test.
Artifact rejection is employed during the t
est phase to reduce the effect of transient noise bursts by the
use of an adaptive rejection threshold. The unit attempts to accept the quieter sections of the test, while
rejecting the noisier portions of the test. When the noise level is approximately constant during the test,
the instrument will tend to accept most of the data in the test. However, as the level of the noise
becomes more variable over time, the instrument will attempt to accept the quieter portions of the
recording. Noise estimates are obtained approximately 32 times per second and a suitable threshold is
estimated from the data. Data segments with a noise floor above this threshold are rejected, which
tends to lower the noise floor of the test. In order to reduce the possibility of obtaining an artificially low
noise floor, the minimum threshold level is limited.
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