Audioscan Verifit - Manual (Page 54)

Verifit ® User's Guide Version 3.12  May 2015
Directional function test
Directional characteristics such as polar plots and Directivity Index (DI) are typically measured in a large
anechoic chamber using sound from one direction and at one frequency at a time. This means they apply only
for a hearing aid set for linear amplification. These are not conditions representative of real use. The Verifit
directional test measures directional performance in real-time while using speech. It is compatible with all forms
of hearing aid processing, including frequency lowering, feedback compensation, and other non-linear
algorithms.
The Verifit directional test presents speech at selectable levels from the left-hand speaker and noise, at a
selectable signal-to-noise ratio, from the right-hand speaker. At periodic intervals, the level of the speech and
noise is momentarily reduced and an additional burst is played from either the left or right speaker to measure
the response from that direction. This burst is extremely fast and will not influence the behavior of the hearing
aid. The coupler SPL is analyzed into two curves labeled L (left) and R (right) to indicate which speaker
generated the curve. The real-time nature of the test allows the operation of adaptive directional systems to be
readily visualized.
Optionally, speech can be disabled which will cause the directional test to alternate noise bursts from the left
and right speakers. This test may not produce a directional response in all hearing aids.
Once directional performance is observed, the test may be terminated.
Because the Verifit test chamber is small and anechoic only at higher frequencies, results are not expected to
agree with data taken in large anechoic chambers. It is a functional test only, providing assurance that the
directional microphone array has been correctly assembled and programmed and has not deteriorated due to
element drift or the clogging of ports. See also On-Ear Instrument Measures.
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