Normal Responses
Before an abnormal emission can be recognised, the normal one must be familiar. A healthy cochlea produces a clear, repeatable emission that rises well above the background noise.
A normal TEOAE
The two recordings you will see most often are the TEOAE response waveform and the DPOAE “DP-gram”. After a click, a healthy ear returns a brief, oscillating emission in the first 20 milliseconds or so. It is small, but it is real and it repeats: record it twice and the two traces look alike.
A normal DP-gram
The DP-gram plots the emission level against test frequency. In a normal ear every point sits comfortably above the noise floor — the shaded band beneath it.
When is an emission “present”?
A response is judged present when two conditions are met together: it must exceed the noise floor by a criterion signal-to-noise ratio, and it must be reproducible. For TEOAEs an acceptable response is commonly described as roughly 3–6 dB above the noise floor; if a reproducible response is not seen at an SNR of at least 3 dB, the outer hair cells of that frequency region cannot be assumed to be functioning normally[10].
Reproducibility is quantified as the correlation between two independently averaged buffers — often labelled A and B. A high waveform-reproducibility percentage, close to 100%, indicates the two buffers agree and the recorded response is genuine rather than noise[9].
How OAEs map onto the audiogram
Normal emissions correspond to good pure-tone hearing, within limits. TEOAEs are present in about 99% of ears when all pure-tone thresholds are better than 20 dB HL, and are essentially always absent once thresholds exceed 40 dB HL; between roughly 25 and 35 dB HL they may or may not appear. DPOAEs behave similarly, though with stronger primaries a reduced DPOAE can sometimes persist with losses up to 50–60 dB HL[10].
| Pure-tone thresholds | Expected TEOAE |
|---|---|
| Better than 20 dB HL | Present (~99% of ears) |
| ~25–35 dB HL | Variable — may be present or absent |
| Worse than 40 dB HL | Absent |
Figures summarise widely cited clinical data[10]; thresholds are approximate and depend on protocol.
Present, present-but-abnormal, absent
Screening reduces the result to pass or refer, but diagnostic interpretation uses three categories. An emission that meets the SNR criterion and falls within the normative amplitude range is present and normal. One that meets the SNR criterion but whose amplitude lies below the normal range is present but abnormal — a meaningful finding that a pass/refer screen would miss. One that fails the SNR criterion is absent. This three-way classification, anchored to frequency-specific normative data, is the basis of the landmark large-scale DPOAE studies[10].
Normal variation: age, sex, and SOAEs
“Normal” is a range, not a single value. Emission amplitudes are notably larger in infants than in adults — by several decibels, more so at high frequencies — which is part of why OAEs work so well for newborn screening. Amplitudes tend to be modestly larger in females than in males, and they decline gradually with age, an effect partly but not entirely explained by accompanying threshold change[11].
The presence of spontaneous emissions is itself a marker of a robust cochlea: ears with SOAEs tend to show larger evoked-emission amplitudes and SNRs. Because of all this variation, the strongest normative comparison is frequency-specific and, ideally, age-appropriate — adult templates can misclassify infant ears, whose emissions are genuinely larger[10].