Verifit
®
User's Guide Version 4.8
©
November 2016
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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Summary of Contents for verifit
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Page 17: ...Verifit User s Guide Version 4 8 November 2016 EC Declaration of Conformity 17...
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Page 107: ...Verifit User s Guide Version 4 8 November 2016 Telecoil test results 107...
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