Frye FONIX 7000 - Manual (Page 92)

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FONIX 7000 Hearing Aid Analyzer
3.5 Digital hearing aids
All digital aids can be tested, but some of the high-end models require a little
more thought and care; these aids have a “noise suppression” feature (also
known as “speech enhancement”). This noise suppression, not to be confused
with the automatic compression of AGC hearing aids, checks if the sound going
into the hearing aid is a continuous signal that could be regarded as noise. If
the aid decides that the sound is noise, it lowers the gain at the corresponding
frequencies. Conventional testing techniques, such as a pure-tone sweep or the
Composite signal, can cause the high-end digital aid to go into this noise reduc-
tion mode. This means that the gain or output you see on the analyzer’s display
will not necessarily reflect the normal response of the aid in speech.
The Digital Speech signal was developed in order to test noise-reducing digital
hearing aids without fear of them going into noise suppression mode. It does
this by taking the standard Composite signal and interrupting it randomly. The
digital hearing aid responds to this modulated signal as it would respond to nor-
mal speech.
3.5.1 Using Digital Speech
The 7000 analyzer seamlessly incorporates the testing of digital hearing aids
into its normal testing procedures.
To test a digital hearing aid, follow the steps outlined in Section 3.4.2, choos-
ing DIG SPEECH in Step 3. Digital Speech can be used to accurately test any
hearing aid, so if you aren’t sure if the hearing aid is digital, you can always use
Digital Speech and be assured that the frequency response is correct.
3.5.2 Changing the Speech Shape
By default, the Digital Speech (and Composite) signal use the ANSI S3.42
speech weighting. This speech weighting rolls off the high frequencies at a rate
of 6 dB per octave, starting with 3 dB down at 900 Hz. Some clinicians, how-
ever, may prefer to use the ICRA speech weighting.
The ICRA speech weighting was taken from a CD of sounds developed by the
International Collegium of Rehabilitative Audiologists (ICRA) and based on the
long term average speech spectrum. The ICRA rolls off the high frequencies
much more quickly than the ANSI spectrum. To switch to using ICRA:
1. Press [MENU] in the Coupler screen.
2. Use [∨, ∧] to select Composite Filter under Measurement Settings. Use the
[START] key to skip ahead sections, if necessary.
3. Use [<, >] to select ICRA.
4. Press [EXIT] to return to the Coupler screen.