Frye FONIX FP40D User Manual
Page 11
Introduction
3
The use of the Composite or Digital Speech signals can uncover the presence of intermodulation
distortion in a hearing aid. Intermodulation distortion is the distortion that results when two or
more frequencies are delivered to the hearing aid simultaneously, resulting in the addition of fre-
quencies to the output that were not present in the input. In other words, when you deliver a com-
plex signal to the hearing aid, such as speech, the aid provides unexpected amplification to some of
the frequencies, causing the entire signal to sound distorted.
Intermodulation distortion can be detected using the composite or digital speech signals and look-
ing for jagged peaks and valleys in the response curve. The curve “breaks up” more and more as the
amount of intermodulation distortion increases.
1.3.2 Probe Option (standard on the FP40-D)
(See Chapter 5 for details.)
The FP40 Hearing Aid Analyzer can be ordered with the Probe Option so that tests can be done on
the hearing aid while it is in the client’s ear. Probe measurements are also known as “real-ear” mea-
surements. It is then possible to individualize the fitting of a hearing aid since a coupler measure-
ment can seldom tell the operator exactly what sound is received by the client. Many factors affect
the sound on its way to the ear drum. When measuring with a probe microphone, you will know
what is happening in the “real ear.”
The probe microphone can also be used as a reference microphone while making coupler measure-
ments.
Target 2-cc Prescription
The Target 2-cc screen on the FP40 converts real-ear targets to coupler targets. It can be used for
ordering hearing aids from a manufacturer, and it can be used for adjusting the hearing aid to tar-
get when a real-ear measurement isn’t possible. Further refinements of the coupler target are pos-
sible using a measured real-ear to coupler difference (RECD) measurement. This is explained in
more detail in Chapter 5.
1.3.3 External Video Monitor
In September 1994, the VGA Color Option was introduced on the FP40. This allowed the FP40 to
be hooked up to an external video monitor. In 1999, we made this a standard feature. When the
VGA display mode is chosen, the LCD is blanked.
When purchasing a VGA monitor for your FP40, it is recommended that you get one with a 0.31 or
0.28mm dot pitch so that you get the resolution needed to take full advantage of the FP40 video
resolution.
1.3.4 Battery Pack Option
Some users may find it convenient to operate their unit away from electrical outlets. These users
can order the Battery Pack Option which will operate on its rechargeable batteries for up to three
hours. (Not available on the FP40-D.)