Other Test Box Measures; Harmonic Distortion; Noise Reduction - audioscan verifit User Manual

17 Other Test Box Measures

In addition to the tests of ANSI S3.22, the Verifit also provides the following tests in the test box:
Manual control: Coupler and test box reference mic. SPL and coupler mic. distortion at selected 1/12th octave
frequencies and stimulus SPL of 0 and 40 – 90 dB in 5 dB steps. Can be used as a dual channel sound level
meter with 1/12th octave, A and C filters.
Directional: A real time assessment of directional performance by analyzing the response to the front and rear
speakers.
Distortion: Harmonic distortion at 2nd or 3rd harmonics and 2nd plus 3rd with input levels varying from 60 –
90 dB SPL.
Multicurve: 1 – 4 curves of coupler SPL or coupler gain for swept tones or pink noise in 1/12th octaves at
selected input SPL of 0 or 40 to 90 dB in 5 dB steps. Can be used as a 1/12th octave spectrum analyzer by
setting stimulus to 0 dB.
Battery drain: A 10 second test of battery current drain with no acoustic input, a 1 kHz 65 dB input SPL, and
an average for 90 dB input SPL at the HFA or SPA frequencies selected in Setup.

Harmonic distortion

This test measures harmonic distortion at 2nd or 3rd harmonics with input levels varying from 60 – 90 dB SPL.
It also presents the sum of 2nd and 3rd harmonics as total harmonic distortion (THD). For hearing aids, this
differs little from true THD.
1. Right-click mouse to raise home menu and select [Distortion] under Test box.
2. Refer to Coupling the hearing instrument, Positioning the hearing instrument and Battery pill use and care to
prepare the instrument.
3. Turn the hearing instrument ON.
4. Click [Start test].
5. Click [Harmonics], then select THD, 2nd or 3rd from the drop-down list.
6. Click [Input], then select the desired input level (60 – 90 dB SPL) from the drop-down list.
7. Click to run the test. Distortion will be displayed at 1/3 octaves in graphic and in tabular form.

Noise reduction

The noise reduction test measures the ability of a hearing instrument to suppress noise. When the test starts,
noise is presented to the hearing instrument at the selected level. The response of the hearing instrument is
captured before the noise reduction activates and is shown as a thick curve on the graph. A comparison curve
shows the hearing instrument reacting to the noise in real-time. The overall RMS noise reduction value in dB
from the captured curve to the current curve is reported. A timer shows the duration of the test. This timer can
be used to determine how long the noise reduction took to activate and for repeated comparisons.
Noise reduction may be run binaurally. In binaural mode, the responses from two hearing instruments can be
observed simultaneously. Select the binaural link before starting a test to enable binaural mode.
To access the Noise reduction test, right-click the mouse to raise the Home prompt and select [Noise Reduction]
under Test-box.
1. Set up the hearing instrument(s) as described in Coupling for binaural/wideband tests.
Verifit ® User's Guide Version 4.8 © November 2016
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