Audioscan Verifit - Manual (Page 74)

Verifit ® User's Guide Version 3.12  May 2015
from the drop-down list. For an adaptive directional instrument, a stimulus level between 60 and 70 dB
should cause the separation to change over a 15 – 45 second period. For a noise-reducing instrument, both
curves may change with time and stimulus SPL.
5. Highlight and <PICK> [Speech S/N] within the Test control poster and select a signal to noise ratio from the
list box. A S/N ratio between 0 and 6 dB will usually induce directional performance after 15 – 45 seconds.
Optionally, highlight and <PICK> [Speech S/N] and select Off. This presents noise alternating between the
front and back test speakers. Speech-adaptive directional instruments may appear non-directional if [Speech
S/N] is Off .
6. Press <Continue> to capture curves or press <Cancel> to abort the test. Captured curves are labeled F (front
speaker response) and B (back speaker response) followed by the test number (1 - 4).
On-ear feedback test
This test shows the LTASS (upper graph) and the power concentration ratio (PCR) (lower graph) for a speech
signal. The PCR measures the degree to which a large amount of power is concentrated at a small number of
frequencies in the hearing aid output (see Freed & Soli in References). In the Verifit, the PCR is the ratio of the
average power of the dominant frequency components in a 1/12 octave band to the power in the entire band,
expressed in dB. Because the gain of a compression hearing aid varies with the signal it is processing, the PCR
is calculated in real time while a speech signal is presented to the hearing aid. The upper graph shows the
LTASS for the speech signal while the lower graph shows the PCR relative to the PCR for speech without
feedback. Feedback results in a peak in the speech spectrum and in the PCR. Incipient feedback results in a
peak in the PCR curve.
Refer to On-Ear Measures - Setup to prepare the system for use and for proper positioning of the client and the
probe tube.
1. Insert the earmold/tip or custom hearing instrument into the ear, being careful not to advance the probe tube
further into the ear canal. A lubricant applied in the vicinity of the probe tube will ease insertion and prevent
slit leaks.
2. Set the instrument as it will be used, with feedback suppression enabled and initialized.
3. Press <Tests> then highlight and <PICK> [On-ear measures], then highlight and <PICK> [Feedback].
4. Highlight and <PICK> Test 1 and set the Stimulus to Speech-std(1) or (2) and the level to 50 or 60 dB SPL.
As the speech passage plays, observe the feedback bar and the lower graph. A yellow Feedback bar and
peaks with yellow markers in the lower curve indicate incipient feedback which may impact sound quality. A
red Feedback bar and peaks with red markers in the lower curve indicate feedback that may be audible and
should be mitigated. Press <Continue> to run the full speech passage and capture average results for the
passage.
5. Repeat for Test 2 and 3 as needed. These tests may be used to explore the effects of jaw movement and the
presence of hands, hats and telephone handsets.
On-ear noise reduction test
This test captures a response curve before the hearing instrument reacts to the presence of noise; a comparison
curve shows the hearing instrument reacting in real-time. The thick curve is the output before the noise
reduction is activated and the thin line is the output as the noise reduction takes effect. The test also provides an
overall rms noise reduction value in dB.
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