Appendix B: Test Sequence - Maico ERO-SCAN Operating Instructions Manual

Operating Instruction
ERO•SCAN
Screening and Diagnostic Version

Appendix B: Test Sequence

A complete test sequence consists of a Probe Check, calibration, and test phase. The Probe
Check phase determines when the calibration phase should proceed, while the calibration
phase calibrates the level of the tones that will be applied during the actual test phase.
Artifact rejection is employed during the test phase to reduce the effect of transient noise
bursts.
Immediately after the test button is pressed, the Probe Check phase of the test begins.
Probe Check phase checks both the quality and stability of the seal by measuring the
response obtained from a sequence of test tones. The stability of the seal is determined by
comparing the responses obtained over time. When the level of the response is within an
acceptable range and is stable over time, the unit proceeds to the calibration phase.
FOR DPOAE
The calibration phase automatically measures the response obtained from a sequence of
calibration tones and calculates the voltage needed to obtain the desired pressures. If the
desired peak pressure cannot be obtained, the unit will use the maximum voltage. A
successful calibration leads to the actual test phase.
The test phase consists of measuring the response obtained from the pairs of test
frequencies (f1, f2) applied to the receivers. Two receivers are used, with each receiver
generating one frequency in order to reduce intermodulation distortion. Frequency domain
estimates of the actual L1, L2, distortion (DP) and noise floor (NF) are obtained via the
discrete Fourier Transform, with a bin resolution of approximately 31 Hz. The NF estimate is
obtained by averaging the power in the 4 closest (+/-2) bins to the DP bin.
FOR 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 test 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
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