Coupler Measurements 73
2. Use [∨, ∧] to select NOISE REDUCTION.
3. Use [<, >] to set the level of noise reduction. This must be at least 2X.
4. Press [NEXT] twice to enter the Custom menu.
5. Use [∨, ∧] to select IMPULSE REJ.
6. Use [<, >] to select the amount of impulse rejection you would like in the
IM distortion test. Lower values will make the FP35 analyzer reject more
measurements. Higher values will make the FP35 analyzer less sensitive.
7. Press [EXIT] to return to the Coupler Multicurve screen to make your IM
measurements. See Section 3.5.2 and 3.5.3.
Note: Impulse rejection applies to all measurements, not just IM distortion.
3.5.6 Using the Reference Microphone
If you are in a noisy testing environment, you might want to use the reference
microphone in order to create more accurate measurements. Remember that any
noise in the testing environment could be amplified by the device and show up
as IM distortion, even though the distortion is coming from the testing environ-
ment and not from the aid itself.
When the reference microphone is turned on, you are no longer measuring
absolute distortion, but relative distortion. That is, you are measuring the differ-
ence between what the measurement microphone is reading inside the coupler
and what the reference microphone is reading outside of the coupler. If there
is noise in the test environment, you will likely see negative distortion values.
To remind you of the difference, the FP35 analyzer displays RLTV on the graph
scale instead of DIST when the reference microphone is turned on.
3.6 CIC Option
The CIC Option is a way of performing a coupler test of a CIC hearing aid that
more accurately reflects the real-ear performance of that aid than a regular 2-cc
coupler measurement. It is not a way to check the manufacturing specifications
of CIC hearing aids because those specifications are based upon 2-cc coupler
measurements.
The CIC Option consists of a CIC coupler and software correction factors. Both
need to be used in order to correctly perform the measurement.
To measure a CIC hearing aid:
1. Attach the CIC coupler to the CIC aid just as you would attach an HA-1 cou-
pler to the aid, and set the hearing aid up for testing as shown in Section
3.3.2.
2. Press [MENU] from the Coupler Multicurve screen.
3. Highlight COUPLER TYPE with the [∨, ∧] keys.
