68 FONIX FP35 Hearing Aid Analyzer
Figure 3.4.2—Measuring a single frequency
3.5 Distortion Measurements
There are several different methods to measure distortion in a hearing aid. This
section describes how to measure harmonic distortion and intermodulation dis-
tortion.
3.5.1 Measuring Harmonic Distortion
Harmonic distortion is when the hearing aid returns energy at frequencies not
present in the source signal. The FP35 allows you test for this phenomenon very
easily. See Section 2.5.1.2 for more information on harmonic distortion.
1. Press [MENU].
2. Select DISTORTION using the [∨, ∧] keys.
3. Select the distortion type desired by using the [<, >] keys.
4. Press [EXIT].
5. Press [F4] to select NORM.
6. Press [START/STOP] to run normal frequency sweep.
After running a normal sweep, the graph will have bars depicting the percentage
level of harmonic distortion at different frequencies. The scale for the harmonic
distortion measurements is given on the right vertical axis of the graph.
