38 FONIX FP35 Hearing Aid Analyzer
2.5.1.6 Three-Frequency Averages
Three-frequency averages are usually performed within an automated test
sequences. When the USER LEVEL is set to ADVANCED (see Section 2.3.2), you
can also perform them from within the Coupler Multicurve, Target Coupler, or
any of the real-ear measurement screens. The three frequencies that are used to
perform the average measurements are chosen in a menu selection and repre-
sented by the last frequency of the three-frequency average. Here is a complete
listing of the available averages.
• HFA1000,1600,2500
• SPA1250,2000,3150
• SPA1600,2500,4000
• SPA2000,3150,5000
• SPA800,1250,2000
• IEC500,1000,2000
Choose the three-frequency average that is closest to that recommended by the
manufacturer. When this average is unknown, choose the average that repre-
sents the frequency range that the aid amplifies the most. The default frequen-
cies are HFA 1000, 1600, 2500.
2.5.2 Understanding Composite Signals
There are two types of composite signals: Composite and Digital Speech. The
Composite signal is a continuous broadband signal containing 79 different fre-
quencies presented simultaneously. This signal is “speech weighted,” which
means that the lower frequencies have a higher emphasis than the higher fre-
quencies.
The Composite signal is both a faster and a more realistic signal than a pure-
tone sweep because there is no waiting for a progression of tones to complete,
and, like speech, a broad spectrum of frequencies is used simultaneously. The
Composite signal updates several times a second.
Digital Speech is an interrupted version of the Composite signal used for test-
ing high end digital hearing aids. Many high end digital aids (though not all)
use a technology called “speech enhancement” or “noise reduction.” These aids
respond to any continuous signal as if it were noise, and lower the gain at the
offending frequencies. Unfortunately, these aids regard the Composite signal or
pure-tone sweeps as noise, making them difficult to test using traditional meth-
ods.
Digital Speech was developed as a way to test these high end hearing aids.
Instead of presenting a continuous signal, it presents an interrupted signal that
the aid regards as speech instead of noise.
