150 FONIX FP35 Hearing Aid Analyzer
5.7.3 Measuring Intermodulation Distortion
This section describes how to make various intermodulation distortion measure-
ments. See Section 2.5.2.2 for technical details on those measurements.
The USER LEVEL must be set to ADVANCED in the Default Settings menu. See
Section 2.3.2 for details.
5.7.3.1 To perform a static IM distortion test
1. Press [MENU] in the real-ear measurement screen to enter the real-ear
menu.
2. Make sure the REF MIC is OFF. Use the arrow keys to make this selection, if
necessary.
3. Press [NEXT] twice to enter the Custom menu.
4. Make sure that DISTORTION is OFF. Use the arrow keys to make this selec-
tion, if necessary.
5. Use [
∨, ∧] to select IM FREQ DIFF.
6. Use [<, >] to select the fixed distance between the primary and second-
ary frequencies used in the measurement. You can choose from no distance
(HARM) to 4000 Hz.
7. Press [EXIT] to return to the real-ear measurement screen.
8. Press and hold down [F4]. This will pop up a list of the available selections,
including DIST.
9. Use [
∨, ∧] to select DIST.
10. Press [START/STOP] to make the selection.
11. Use [
∨, ∧] to select the RMS source of the test. Each frequency will have an
amplitude 3 dB less than the RMS source.
12. Set up the client, the aid, and the analyzer for real-ear testing. Make sure to
level the sound field speaker.
13. Press [START/STOP] to start the static IM distortion measurement. See
Figure 5.7.3.1.
14. Use [<, >] to change the primary frequency of the test. The secondary fre-
quency will also change, remaining a fixed distance (selected in Step 6)
away from the primary frequency.
15. Press [START/STOP] to stop the measurement.
