Audioscan Verifit 2 User Manual

Page 148

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Verifit

®

User's Guide Version 4.2 © June 2015

FM System, an assistive listening device consisting of a microphone, an fm radio transmitter and an fm
receiver. The microphone and transmitter are worn by the speaker and the receiver is worn by the listener.

Gain (in dB), output sound pressure relative to input sound pressure, expressed in decibels; gain = 20log10
(output sound pressure / input sound pressure); also, gain = (output SPL) - (input SPL).

Gain control, a manually or electronically operated control for the adjustment of overall gain (ANSI S3.22).

HA-1 Coupler, a coupler having a volume of 2 cubic centimetres with direct access to the cavity. Used for
testing in-the-ear and in-the-canal hearing aids; can also be used to test behind-the-ear hearing aids with a
custom earmold attached. Aka the ITE coupler.

HA-2 Coupler, a coupler having a volume of 2 cubic centimetres with access through a rigid tube. When used
for testing BTE hearing aids, the rigid tube consists of 18 mm of 3 mm tubing plus 25 mm of 2 mm tubing
(ANSI S3.22). When used for calibrating insert earphones, the 2 mm tubing is not used (ANSI S3.6). Aka the
BTE coupler.

Harmonic, a component of a tone complex that is an integer multiple of the lowest frequency component
(fundamental).

Harmonic Distortion, the addition of harmonic components to a signal. The rms value of a harmonic
component of a signal as a percentage of the rms value of the fundamental. If less than 20%, the rms value of
the total signal may be used instead of the fundamental.

HFA, High Frequency Average, the average of values in dB at 1000, 1600, and 2500 Hz. (ANSI S3.22).

HL, Hearing Level, the hearing threshold referenced to the threshold of normal hearing, expressed in dB.

HI, Hearing instrument.

Input Compression, a form of AGC in which the signal level is regulated before the volume control.

Input / Output function, steady state, single-frequency plot of the coupler SPL on the ordinate as a function of
input SPL on the abscissa with equal decibel scale divisions on each axis (ANSI S3.22).

ITE, In-The-Ear (hearing aid).

Kneepoint (compression threshold), the point on an input/output curve at which the slope digresses from unity
indicating the signal level at which a non-linear process begins to take effect.1

LCD, liquid crystal display. A thin, planar information display.

Linear Amplification, amplification having the same gain for all input levels until the maximum output of the
device is reached.

LTASS, Long-term average speech spectrum, the rms level of a speech passage in 1/3rd octave bands,
averaged over the entire passage.

MAP, minimal audible pressure, SPL of a tone, measured or inferred at the tympanic membrane, at the
threshold of audibility.

MPO, Maximum Power Output, the maximum SPL that a hearing aid can deliver in response to a steady
narrow band input. The stimulus may be pulsed (a tone burst) to avoid discomfort and to approximate an aided
UCL measurement stimulus.

Modulation, the process of varying a characteristic of one signal with another.

NAL, National Acoustic Laboratories (Australia)

NCA, National Centre for Audiology (Canada)

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