Audioscan Axiom - Manual (Page 93)

Axiom ® User's Guide Version 1.8  May 2015
fittings - it doesn’t matter how the sound reaches the TM, the perception is the same. However, the sound that
escapes from a vent or open fitting may be detected by the on-ear reference microphone, interfering with the
sound-field equalization. For this reason, the hearing instrument must be muted during sound-field equalization.
1. With Speechmap in the [On-ear] mode, click on the [Verification] button and select [Open] from the
Instrument pull-down menu.
2. Position the client and probe tube and enter audiometric data. See On-Ear Measures - Setup, Speechmap, and
Fitting to targets for soft and average speech and Adjusting the Maximum Output Level.
3. Place the open-fit hearing instrument on the ear with the probe tube in place, making sure to mute the
hearing instrument.
4. Access Test 1, 2 or 3. If this is the first test since selecting Open, you will be prompted to mute or turn off
the hearing instrument and click on the Equalize button on the setup poster. After equalization, unmute or
turn the instrument on and follow the fitting procedures presented previously in this section. It is necessary
to repeat the Equalize procedure whenever the client or nearby objects are moved.
Verifying Frequency Compression/ Frequency-Lowering
Hearing Instruments in Speechmap
Frequency lowering is used when it is not possible to amplify the high frequency components of speech
sufficiently to raise them above threshold. In this case, the high frequency components may be shifted to a
lower frequency with a better hearing threshold where the available gain will render them audible.
Four modified versions of the Speech-std (1) test stimulus (Speech3150, Speech4000, Speech5000 and
Speech6300) are provided in Speechmap to assist in verifying and adjusting frequency lowering devices. In
each of these modified test stimuli, the 1/3 octave band levels above 1000Hz are reduced by 30dB, except for an
isolated 1/3 octave band centered at the frequency indicated in the selected test stimulus’ name. With these
reduced band levels, the resulting LTASS produces a distinct 'cavity' between 1000Hz and the selected high
frequency band, as seen below for the FM Boom test signal.
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