Appendix C: Test Sequence
A complete test sequence consists of an AutoStart, calibration, and test phase. The AutoStart 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 AutoStart phase of the test begins. AutoStart 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 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.
