Frye FONIX 7000 - Manual (Page 45)

General Operation
37
tone sweeps with speech-weighted Composite or Digital Speech signals. For this
reason, we have made it possible to “weight” the real-ear pure-tone sweeps on
the 7000 hearing aid test system.
The TONE FILTER selection is available in the Setup Menu under Real-ear set-
tings and in the local menus of the Real-Ear Insertion Gain and Real-Ear SPL
measurements screens. It has the following settings:
• FLAT: Uses a flat weighted signal with equal amplitudes of all the tones
in the sweep
• ANSI: Uses the ANSI weighting in the pure-tone sweep
• ICRA: Uses the ICRA weighting in the pure-tone sweep
• AUTO: Uses the ANSI weighting for measurements below 85 dB SPL and
the FLAT weighting for measurements at 85 dB SPL and above.
Pure-tone measurements made in the coupler measurement screens are always
flat weighted.
2.3.2 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 usually “speech weighted,”
which means that the lower frequencies have a higher emphasis than the high-
er frequencies.
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.
The Composite and Digital Speech signals can be used with several different
types of speech weightings: ANSI, ICRA, and FLAT. Flat is generally only used
for specific research purposes—it contains no speech weighting and is difficult
for most hearing aid circuits to process. See Section 2.3.2.3 for a discussion of
the ANSI and ICRA speech weightings.