Coupler Measurements 47
• You must position the reference microphone properly. If you don’t have the reference micro-
phone positioned next to the microphone of the hearing aid, you will get inaccurate results.
Worse, if you leave the reference microphone outside the chamber when it is turned on, you
will get wildly inaccurate test results.
To turn on the reference microphone:
1. Press F1 to enter the General Setup Menu.
2. Use the AMPLITUDE and FREQUENCY knobs to select REFERENCE MIC under COUPLER
SETTINGS.
3. Press START/STOP to toggle the selection from OFF to ON.
4. Press F1 to return to the Main Coupler Screen. You will read REFEENCE MIC ON in the
STATUS box.
Figure 3.4.9A—Test setup for BTE aid using 3.4.9B—Test setup for ITE aid using
reference microphone. reference microphone
3.5 Digital Aids
All digital aids can be tested, but some of the high-end models requires a little more thought and
care; these aids have a “noise suppression” (or “speech enhancement”) feature. This noise sup
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pression feature, not to be confused the automatic compression of AGC hearing aids, checks if the
sound going into the hearing aid is a continuous signal that could be regarded as noise. If the aid
decides that the sound is noise, it lowers the gain at the corresponding frequencies. Conventional
testing techniques, such as a pure-tone sweep or a Composite signal, can cause the high-end digital
aid to go into this noise suppression mode. This means that the gain or output you see on the ana
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lyzer’s display will not necessarily reflect the normal response of the aid to speech.
