70 FONIX FP35 Hearing Aid Analyzer
3. Press [NEXT] to enter the Advanced menu.
4. Select IM FREQ DIFF using [∨, ∧].
5. 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.
6. Press [EXIT] to return to the Coupler Multicurve screen.
7. Press and hold down [F4]. This will pop up a list of the available selections,
including DIST.
8. Use [
∧,∨] to select DIST.
Figure 3.5.2—Measuring intermodulation distortion
9. Press [START/STOP] to make the selection.
10. Set up the aid in the sound chamber for testing as usual. Make sure to close
the lid of the sound chamber.
11. Press [START/STOP] again to start the static IM distortion measurement. See
Figure 3.5.2.
12. Use [<, >] to change the primary frequency of the test. The secondary fre-
quency will also change, remaining a fixed distance (selected in Step 5)
away from the primary frequency.
13. Use [∨, ∧] to change the RMS source of the test signals. Each signal will
have an amplitude 3 dB below the RMS source.
14. Press [START/STOP] to stop the measurement.
